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This fastener glossary
provides definitions of fasteners and
fastener terms. It is intended to assist fastener
buyers, fastener purchasers, Original Equipment
Manufacturers (OEM's) and engineers.
One-Way Head Screw:
A round head screw which is slotted but has side
clearances at diagonally opposite sides of the slot
so that the screw can be driven only in the
direction of assembly, designed for preventing
tampering.
Open Washer:
A washer with one side open so as to be removed or
put under a nut without removing the nut.
Oval Binding Head Screw:
Obsolete term for a truss head screw.
Oval Head:
Rounded top surface and a conical bearing surface
with an included angle usually of 82 degrees.
Oval Point:
A rounded end which is used, particularly for set
and adjusting screws, to apply pressure without
cutting action.
Oven Head Screw:
Obsolete term for truss head screw.
Oxidation:
(1) A reaction in which there is an increase in
valence resulting from a loss of electrons. Contrast
with reduction. (2) A corrosion reaction in which
the corroded metal forms an oxide; usually applied
to reaction with a gas containing elemental oxygen,
such as air.
Pan Head:
Flat top surface rounded into cylindrical sides, and
a flat bearing surface. The recessed pan head has a
rounded top surface blending into cylindrical sides
and a flat bearing surface.
Passivate:
A very confusing term, since the common usage has
taken on a different meaning than the technical
definition. In past experience, users (including
engineers) of commercial fasteners seldom mean the
old technical terminology. Technically, passivating
is not cleaning but is a process of dipping
fasteners into a nitric acid solution to rapidly
form a chromium oxide on the surface of the
material, creating a passive film that protects
stainless from further oxidation. The purpose of
passivating is to remove both grease left from
manufacturing and traces of steel particles which
may have rubbed off manufacturing tools onto the
fastener. In common commercial parlance (meaning
non-military and aerospace), passivating means
cleaning to users, and the terms “passivating” and
“cleaning” are used interchangeably. A wide range of
cleaning methods using different mixtures containing
nitric, phosphoric and other acids or simply
exposing cleaned stainless fasteners to air for a
period of time will result in a “passivated”
condition. For fasteners that have been properly
cleaned, it is impossible to determine the method of
cleaning or passivation that was used.
Passive Film:
The major characteristic of stainless is its ability
to form a thin layer of protection, called a
“passive film”, on its outside surface. This film
results from a continual process of low-level
oxidation, so oxygen from the atmosphere is needed
for the passive film to exist. Once formed, it
prevents further oxidation or corrosion from
occurring. Even if chipped or scratched, a new
passive film on stainless will form.
Pattern Nuts:
Special nuts usually furnished in plain or chamfered
face unless otherwise specified, and threads are
unified Coarse or unified Fine, Class 2B. (also
small and extra small)
Peening:
The stretching of metal by hammering or rolling the
surface.
pH:
A measure of the acidity or alkalinity of a
solution; The negative logarithm of the hydrogen-ion
activity; it denotes the degree of acidity or
basicity of a solution. At 25 ºC (77 ºF), 7.0 is the
neutral value. Decreasing values below 7.0 indicate
increasing acidity; increasing values above 7.0,
increasing basicity.
Phillips Recessed Head:
Wall Street Journal article, Phillips Screws -
Fasteners from Hell? by Rich Hirsch, "The screw was
invented in the early 30’s by Henry F. Phillips, a
Portland, Oregon businessman. He knew that car
makers needed a screw that could be driven with more
torque and that would hold tighter than slotted
screws. Car makers also needed a screw that would
center quickly and easily, and could be used
efficiently on an assembly line. The Phillips screw
was designed so that it could be driven by an
automated screw driver with increasing force until
the tip of the driver popped out without ruining the
screw head. So what many consider a design flaw is
actually a feature (at least if you’re a car
manufacturer). The Phillips screw first gained
acceptance with Cadillac in the late 30’s. Although
there is a Phillips Screw Co. today, the company
never actually made Phillips screws or drivers. They
were produced under license by other companies.
Unlicensed knockoffs proliferated, so that in 1949,
Mr. Phillips was stripped of his patent." One of the
complaints about Phillips Drive is they slip (camout)
easily. "Phillips screws were designed to cam out.
They were invented to prevent unskilled industrial
workers from overdriving fasteners. The tapered
wings of Phillips drivers act as a clutch that
forces drivers out of screw sockets after the screws
are driven home. But the tradeoff is that workers
have to lean hard on the drivers to prevent unwanted
slippage." American Heritage Invention & Technology
Fall 2001 advises "Phillips founded the Phillips
Screw Company to license his patents. After three
years of rejection, he finally persuaded the
American Screw Company to manufacture the screws.
Engineers there balked until the president of the
company threatened to fire anyone who said it
couldn’t be done. American Screw then spent $500,000
developing a manufacturing process and induced
General Motors to use the screws on its 1936
Cadillac. By 1940 virtually every American automaker
had switched to Phillips screws....Phillips himself
died in semi-obscurity in 1958 at the age of 68, long
after his invention had become a household name. "
Phosphorus:
A non-metallic substance that lowers the rate of
oxidation, thereby helping resist corrosion.
Physical Properties: Those properties familiarly diiscussed in physics,
including those descriabed under mechanical
properties; for example, density, electrical
conductivity, co-efficient of thermal expansion.
Pickling:
Removing surface impurities by using chemicals.
Pilot Point:
Similar to a “B” point, a pilot point is a small
(perhaps 1/8” - 1/4”) unthreaded blunt portion at
the end of a sheet metal or drive screw. Commonly
used in the fenestration industry.
Pinch Point:
A sharp conical point, usually of 45 degrees
included angle, formed by a pinching operation.
Pitch:
The nominal distance between two adjacent thread
roots or crests.
Pitch Diameter:
Approximately in-between the major and minor
diameters.
Pipe Caps:
A cap that threads onto a pipe (like a nut) to seal
one end.
Pipe Fittings:
The term applying to all forms of connecting parts
which join pieces of pipe together.
Pipe Plugs:
A short piece of threaded pipe, Slotted, Square Head
or Socket, used to close up one end of a fitting.
Pipe Screw Thread:
American Standard pipe threads are tapered 1 inch in
16, or 3/4 inch per foot. They are 60 degree
threads, of National form with flat or rounded top
and bottom.
Pitch:
The distance, measured parallel to its axis, between
corresponding points on adjacent thread forms in the
same axial plane and on the same side of the axis.
Pitch Diameter:
On a straight thread, the diameter of the coaxial
cylinder, the surface of which would pass through
the thread profiles at such points as to make the
width of the groove equal to one-half of the basic
pitch. On a perfect thread this occurs at the point
where the widths of the thread and groove are equal.
Pitch Line:
A generator of the cylinder or cone of a screw
thread specified in the definition of pitch
diameter.
Pits: Sharp
depressions on the surface of a raw material or
fastener.
Pitting Corrosion:
Pitting indicates deep corrosion in localized spots
on a fastener. Dirt or grease on certain portions of
a fastener may block oxygen from that surface, thus
impeding the passive film which protects stainless
from corrosion.
Plain Sheared Point:
The end of a fastener cut approximately flat and
square to the axis, without chamfer.
Planer Head Bolt:
A bolt havinig a large low square head, designed for
insertion in T-slots of planer, shaper, or milling
machine tables.
Plane Strain:
The stress condition in linear elastic fracture
mechanics in which there is zero strain in a
direction normal to both the axis of applied tensile
stress and the direction of crack growth (that is,
parallel to the crack front); most nearly achieved
in loading thick plates along a direction parallel
to the plate surface. Under plane-strain conditions,
the plane of fracture instability is normal to the
axis of the principal tensile stress.
Plane Stress:
The stress condition in linear elastic fracture
mechanics in which the stress in the thickness
direction is zero; most nearly achieved in loading
very thin sheet along a direction parallel to the
surface of the sheet. Under plane-stress conditions,
the plane of fracture instability is inclined 45º to
the axis of the principal tensile stress.
Plate:
The electro-chemical coating of a metal piece with a
very different metal.
Polarization:
(1) The change from the open-circuit electrode
potential as the result of the passage of current.
(2) A change in the potential of an electrode during
electrolysis, such that the potential of an anode
becomes more noble, and that of a cathode more
active, than their respective reversible potentials.
Often accomplished by formation of a film on the
electrode surface.
Polish:
To make smooth or lustrous by friction with a very
fine abrasive.
Pop Rivet:
A headed blind fastener in wide use. Pop is a
registered trademark to Emhart Fastening
Technologies. The term "pop rivet" has become a
widely used and generic term, much like Coke is to
the soft drink industry. If brand susbstitution is
unacceptable, you should specify Pop brand only.
Powder Coating:
Powder coating is an advanced method of applying a
decorative and protective finish to a wide range of
materials and products that are used by both
industries and consumers. The powder used for the
process is a mixture of finely ground particles of
pigment and resin, which is sprayed onto a surface
to be coated. The charged powder particles adhere to
the electrically grounded surfaces until heated and
fused into a smooth coating in a curing oven. The
result is a uniform, durable, high-quality, and
attractive finish.
Precipitation Hardening:
Hardening caused by the precipitation of a
constituent from a supersaturated solid solution.
Precipitation Hardening Stainless:
(AISI 17-4PH) is a nickel chromium stainless with
cobalt and tantalum. The alloying agents produce
high strength and ductility, good machinability and
weldability. Hardening is by aging the cold steel at
900 degrees F for 4 hours followed by air cooling.
Not used for cold forming but commonly used for
high-strength, corrosion resistant screw machine
parts.
Precision Machine Screws:
Slotted machine screws, milled from bar, cut thread,
and are machined finished Class 3A fits.
Preload:
The tension created in a fastener when first
tightened. Reduces after a period of time due to
embedding and other factors.
Prevailing Torque:
The torque required to run a nut down a thread on
certain types of nuts designed to resist vibration
loosening. The resistance can be provided by a
plastic insert or a noncircular head.
Principal Stress (Normal):
The maximum or minimum value at the normal stress at
a point in a plane considered with respect to all
possible orientations of the considered plane. On
such principal planes the shear stress is zero.
There are three principal stresses on three mutually
perpendicular planes. The state of stress at a point
may be (1) uniaxial, a state of stress in which two
of the three principal stresses are zero, (2)
biaxial, a state of stress in which only one of the
three principal stresses is zero, and (3) triaxial,
a state of stress in which none of the principal
stresses is zero. Multiaxial stress refers to either
biaxial or triaxial stress.
Process Annealing:
Heating a ferrous alloy to a temperature close to,
but below, the lower limit of the transformation
range and then cooling, in order to soften the alloy
for further cold working.
Proof Load:
The proof load of a nut is the axially applied load
the nut must withstand without thread stripping or
rupture, that of a bolt, screw or stud is the
specified load the product must withstand without
permanent set. Usually 90% of yield strength.
Property Class:
A designation system which defines the strength of a
bolt or nut. For metric fasteners, property classes
are designated by numbers where increasing numbers
generally represent increasing tensile strengths.
The designation symbol for bolts consists of two
parts: 1. The first numeral of a two digit symbol or
the first two numerals of a three digit symbol
approximates 1/100 of the minimum tensile strength
in MPa. 2. The last numeral approximates 1/10 of the
ratio expressed as a percentage between minimum
yield stress and minimum tensile stress. Hence a
fastener with a property class of 8.8 has a minimum
tensile strength of 800 MPa and a yield stress of
0.8x800=640 MPa. The designation system for metric
nuts is a single or double digit symbol. The
numerals approximate 1/100 of the minimum tensile
strength in MPa. For example a nut of property class
8 has a minimum tensile strength of 800 MPa. A bolt
or screw of a particular property class should be
assembled with the equivalent or higher property
class of nut to ensure that thread stripping does
not occur.
Punch:
(v) To perforate by pressing a non-rotating tool
through the work.
Quench-age Embrittlement:
Embrittlement of low-carbon steels resulting from
precipitation of solute carbon at existing
dislocations and from precipitation hardening of the
steel caused by differences in the solid solubility
of carbon in ferrite at different temperatures.
Quench-age embrittlement usually is caused by rapid
cooling of the steel from temperatures slightly
below Ac, (the temperature at which austenite begins
to form), and can be minimized by quenching from
lower temperatures.
Quench Hardening:
Hardening a ferrous alloy by austenitizing and then
cooling rapidly enough so that some or all of the
austenite transforms to martensite.
Quenching:
Rapid cooling. When applicable, the following more
specific terms should be used: direct quenching, fog
quenching, hot quenching, interrupted quenching,
selective quenching, spray quenching, and time
quenching.
Ream:
To finish a drilled or punched hole very accurately
with a rotating fluted tool of the required
diameter.
Reamer:
Tool used for enlarging holes previously formed by
drilling or boring.
Recessed Head:
A screw head, having specially formed indentations
or recesses centered on the head, into which a
suitably formed driver fits.
Reduction of Area:
A measurement like elongation which is related to
the tensile strength of a fastener. While elongation
measures the length of a fastener stretched to its
breaking point compared to its original length,
reduction of area measures the diameter of a
fastener just before breaking compared to its
original diameter.
Relaxation:
The loss of clamping force in a bolt which commonly
occurs as a result of embedment. Can also be caused
by gasket creep, differential temperature expansion
or vibration loosening.
Relief:
The amount one plane surface of a piece is set below
or above another plane, usually for clearance or for
economy in machining.
Ribbed Neck Carriage Bolt:
A plain, circular, oval head bolt with a serrated
neck to prevent rotation.
Right-Hand Thread:
A thread is a right hand thread if, when viewed
axially, it winds in a clockwise and receding
direction.
Rivet:
A headed metal fastener of some malleable material
used to join parts, as metal plates, of structures
and machines by inserting the shank through a hole
in each piece and forming a head on the headless
end.
Rivet Bolt:
A bolt designed as a substitute for rivets, having a
button head, a ribbed shank, a UNC thread, or a
special thread such as a Dardalet thread or Lok-Thread
(TM).
Robertson Drive:
While the Phillips drive is the most commonly used
in the United States, the Robertson drive is on 85%
of screws sold in Canada. In 1908 Peter Lymburner
Robertson invented the Robertson square drive and
established the Robertson Screw Company in Milton,
Ontario. Henry Ford, the largest automaker in North
America was approached and it was discovered a
switch from slotted to Robertson would save the
automaker two hours in the assembly time of an
automobile. When Robertson refused to grant Ford a
license to manufacture the screw, a possible
relationship crumbled. A few years later, Henry
Phillips sold Ford the phillips drive, and the rest
is history. Phillips became the most popular screw
in the US and Robertson became the most popular in
Canada.
Rockwell Hardness Test:
A measure of hardness by determining the depth of
penetration of a pentrator into the specimen under
certain fixed conditions of test. The penetrator my
be either a steel ball or a diamond sphero- conical
penetrator. The hardness number is related to the
depth of indentation and the higher the number the
harder the material.
Rod Ends:
The ends of connecting rods which fit over crank
pins or cross head pins.
Roll Threading:
Applying a thread to a bolt or screw by rolling the
piece between two grooved die plates, one of which
is in motion, or between rotating grooved circular
rolls.
Rolled Point:
The point frequently produced by the cupping of the
last 1 to 1 1/2 threads by the thread roling
pressure. This type of point is not produced
intentionally but is considered as an alternative
form of the plain sheared point.
Root:
That surface of the thread which joins the flanks of
adjacent thread forms and is identical with or
immediately adjacent to the cylinder or cone from
which the thread projects.
Root Diameter:
Refers to the minor diameter on screws or the major
diameter on nuts.
Round Head:
Semi-elliptical top surface and flat bearing
surface.
Rust:
A visible corrosion product consisting of hydrated
oxides of iron. Applied only to ferrous alloys.
Sacrificial Protection:
Reduction of corrosion of a metal in an electrolyte
by galvanically coupling it to a more anodic metal;
a form of cathodic protection.
SAE Specifications: Standards developed by the Society of Automotive
Engineers, Inc.
SAE Standard Screw Threads:
The SAE Screw Thread Standard, as revised in 1954,
conforms with the Unified and American Standard (ASA
B1.1-1949).
Salt Fog Test (also Salt Spray Test):
An accelerated corrosion test in which specimens are
exposed to a fine mist of a solution usually
containing sodium chloride, but sometimes modified
with other chemicals.
Scale:
A discoloring or oxidation on the surface of hot
forged fasteners.
Screw Machine:
Cutting and removing material in order to form a
fastener.
Screw:
Very confusing term but we use the following - Bolts
are defined as headed fasteners having external
threads that meet an exacting, uniform bolt thread
specification (such as M, MJ, UN, UNR, and UNJ) such
that they can accept a nontapered nut. Screws are
defined as headed, externally-threaded fasteners
that do not meet the above definition of bolts.
Screw Machine:
June 3, 1856 - Cullen Whipple, a mechanic from
Providence, RI, patents the first automatic machine
for producing screws
Screw Stock:
Metal in the form of wire or rod, ordinarily a free-machining
type of alloy, used for making screw machine
products.
Screw Thread: A ridge of uniform section in the form of a helix on
the external or internal surface of a cone or
frustum of a cone. A thread formed on a cylinder is
known as a straight or parallel thread, to
distinguish it from a taper thread which is formed
on a cone of frusetum of a cone.
Screw Thread Chasers:
Cutting tools having teeth spaced to match the pitch
of the threads to be cut.
Secondary Operations:
Operations which include punching, shaving,
trimming, drilling, sawing, milling, pointing,
tapping and polishing, etc., are generally called
secondary.
Season Cracking:
An obsolete historical term usually applied to
stress-corrosion crackling of brass.
Self Drilling Screw:
Screw that drills and taps its own hole.
Self-Locking:
Where binding action is self-induced on the body of
the bolt, screw or nut to keep it rigid and prevent
movement and vibration.
Self Tapping Screws:
See "Tapping Screws".
Semi-Finished Hexagon Bolts: Bolts with standard sizes ranging from 1/4" through
4". Class 2A tolerance. The bearing surface is
washer faced.
SEMS:
A screw and washer assembly. A screw or bolt which
has a captive washer. The washer is frequently loose
on the plain shank of the fastener, the shank
diameter being equal to the effective diameter of
the thread; the thread being rolled from this
diameter. The origin of the word is a frequent
question. In the 1930's E. C. Crowther was a
representative for a company that sold both
shakeproof washers and screws. He came up with the
idea of placing the washer on the screw before it
was thread rolled. The major diameter of the screw
being larger than the washer hole prevents it from
coming off. The Illinois Tool Works made machines
that produced these patented pre-as"SEM"bled washers
and screws. In spite of the original patents and
trademarks the word SEMS is generally recognized as
a generic term applicable to screw and washer
assemblies.
Sensitizing Heat Treatment:
A heat treatment, whether accidental, intentional,
or incidental (as during welding), that causes
precipitation of constituents at grain boundaries,
often causing the alloy to become susceptible to
intergranular corrosion or intergranular
stress-corrosion cracking. See also sensitization.
Sensitization:
In austenitic stainless steels the precipitation of
chromium carbides, usually at grain boundaries, on
exposure to temperatures of about 550 to 850 ºC
(about 1000 to 1550 ºF), leaving the grain
boundaries depleted of chromium and therefore
susceptible to preferential attack by a corroding
(oxidizing) medium.
Set Screw Points:
A screw with various type points, cup, cone, flat,
oval, half dog, full dog, hanger or knurled, used to
hold or "set" a collar on a shaft or hold pieces of
this kind against movement. Screws are usually
short, threaded entire length with the various type
points for different applications against this
movement.
Set Screw:
An externally threaded fastener with or without a
head and having a formed point, designed to prevent
relative movement of parts when screwed through one
part upon or into another part. Point types include:
Cup - hollowed end and is the most commonly used
point style. Used when the digging in of the point
is not undesirable.
Cone - Pointed end, this type generates the highest
torsional holding power and is typically used for a
permanent connection.
Oval - Rounded end that is typically used when
frequent adjustment is required. The oval end
prevents/reduces indentation.
Flat - Cause little damage to the shaft and are used
when frequent adjustment is required.
Dog - Flat end with the threads stopping short of
the end with the end fitting into a hole.
Shank:
That portion of a bolt between the head and the
threaded portion.
Shank Diameter:
The shank diameter is the diameter of the shank of
an unthreaded fastener. The diameter of the
unthreaded portion of a threaded shank is termed the
Body Diameter.
Shear:
To cut off sheet or bar metal between two blades.
Shear Strength:
The stress required to produce fracture when
impressed vertically upon the cross-section of a
material. Expressed in psi. Measured by the push or
pull against the side of a fastener until the
fastener breaks (for example, moving an object
continually against the side of a screw that is
protruding from a wall). As a rule of thumb, shear
strength is two-thirds of tensile strength.
Shim:
A thin spacer of sheet metal used for adjusting.
Sigma Phase:
A hard, brittle, nonmagnetic intermediate phase with
a tetragonal crystal structure, containing 30 atoms
per unit cell, space group P42mnm, occurring in many
binary and ternary alloys of the transition
elements. The composition of this phase in the
various systems is not the same and the phase
usually exhibits a wide range in homogeneity.
Alloying with a third transition element usually
enlarges the field of homogeneity and extends it
deep into the ternary section.
Sigma-Phase Embrittlement:
Embrittlement of iron-chromium alloys (most notably
austenitic stainless steels) caused by precipitation
at grain boundaries of the hard, brittle
intermetallic sigma phase during long periods of
exposure to temperatures between approximately 560
and 980 ºC ( 1050 and 1800 ºF). Sigma-phase
embrittlement results in severe loss in toughness
and ductility, and can make the embrittled material
susceptible to intergranular corrosion. See also
sensitization.
Silicon:
A non-metallic substance that adds strength and
toughness to copper to help form a bronze alloy.
Silicon Bronze:
An alloy made of 95% - 98% copper plus a small
amount of silicon added for strength. Small amounts
of manganese and aluminum may also be added for
strength, and lead may be added for machineability.
Silicon bronze is non-magnetic with a high degree of
thermal conductivity and high corrosion resistance
against sea water, gases, and sewage. It is often
used by the utilities industry for pole line
hardware and switchgear equipment, mine sweeping,
sewage disposal equipment, food machinery, marine
applications, plumbing and liquid handling.
Surprisingly, silicon bronze is only a low to
moderate conductor of electricity, though it is a
better conductor than stainless.
Single Thread:
A single-start thread having lead equal to the
pitch.
Sleeve Anchor:
The sleeve anchor is a light to medium duty
pre-assembled anchor. It is ideal for applications
in hollow masonry as well as concrete.
Sleeve Nut: A long nut with right or left threads for connecting
two rods to make an adjustable member.
Slip Washer:
A washer with an opening large enough to slip the
washer over a bolt, and under the bold head. Also
called a C washer.
Slotted Head:
The head, of a bolt or screw, which has one or more
slots across the top to fit a screw driver. The
first known use of a slotted head screw as we know
it was by a German clock maker in 1513.
Slotted Nut:
A hexagon nut having opposed slots at the end
opposite to the bearing face which are perpendicular
to the axis, designed for insertion of a cotter to
secure the nut in place when used wiht a drilled
fastener.
Slotted Pin:
A pin that has a slot, either a square or round
bottom, into which an external clip or key is
affixed in a locking position.
Socket Head:
A recessed head in which the sides of the recess are
parallel to the body axis, into which a wrench fits.
The recess is commonly hexagonal or fluted in form.
Also designated as "internal wrenching head".
Socket Head Cap Screw:
A screw with a round head with usually a hexagon
indentation in the head for tightening purposes.
Typically used on machine parts.
Solution Annealed: Or Carbide Solution Annealed - A process of heating
and removing carbide precipitants (carbon that has
broken loose from its stainless steel solution) by
heating a finished fastener to over 1,850 degrees F.
and cooling it quickly, usually in water, so carbon
content goes back into the stainless solution.
Spacers:
Pieces designed to prevent crushing of sandwich-type
and other lightweight structural materials at
fastening points. Sometimes called inserts.
Spacers, Threaded:
Spacers with threads through which a bolt can be
put. This saves weight by eliminating the nut and
the reduction of the bolt length.
Spanner Screws:
Special unslotted screws surface, in Round undrilled,
Flat drilled and others, that require a special
wrench.
Spanner Wrenches:
Tools used to turn and tighten spanner screws.
Spline:
Raised portions of a shaft which fit into
corresponding grooves in a pulley or some sliding
member. They can either permit end movement or can
be used as permanent fastening.
Spline Nut:
A nut having external splines or ribs which hold it
in place when forced into a hole of slightly smaller
diameter.
Spline Socket:
A recessed socket in the head of a bolt or screw to
develop greater torque or driving ease without
"round" the recess.
Split Rivet:
A small rivet having a split end for securing by
spreading the ends.
Spot-Face:
To finish a round spot on a rough surface, usually
around a drilled hole, to give a good seat to a
screw or bolthead, cut, usually 1/16 inch deep.
Spring Lockwasher:
A hardened coil wire having a slightly trapezoidal
section after forming which functions as a spring
take-up device to compensate for developed looseness
and the loss of tension between the parts of an
assembly and to prevent the nut from turning.
Square Neck Carriage Bolt:
A plain, truss or oval head bolt with a square neck
to prevent rotation.
Square Nuts:
Nuts that are square rather than hexagonal.
Stainless:
1. A trade name given to alloy steel that is
corrosion and heat resistant. The chief alloying
elements are chromium, nickel and silicon in various
combinations with a possible small percentage of
titanium, vanadium, etc. 2. By AISI definition, a
steel is called "Stainless" when it contains 4 per
cent or more chromium.
Stainless Steels:
With the addition of 12% chromium to iron, stainless
steel is formed. The chromium protects the iron
against most corrosion or red-colored rust; thus the
term “stainless” steel. The ability of stainless to
form a thin layer of protection on its outside
surface, called a “passive film”, is its most
important characteristic in preventing corrosion
(see PASSIVE FILM). The overriding purpose of
stainless steel is to provide corrosion resistance
against: (a) atmospheric conditions such as carbon
dioxide, moisture, electrical fields, sulfur, salt,
and chloride compounds; (b) natural and artificially
produced chemical, (c) extremes of weather where
cold temperatures cause brittleness and hot
temperatures reduce strength and increase corrosion.
Standard Fastener:
A standard fastener is a fastener which conforms in
all respects to recognized standards.
Stamping: Punching out parts with dies, usually referring to
flat washers.
Static Friction:
Friction at rest; a force is required to initiate
relative movement between two bodies - static
friction is the force that resists such relative
movement. Sometimes referred to as stiction.
Step Bolt: A plain, circular, oval head bolt with a square neck
to prevent rotation.
Stress Area:
The effective cross sectional area of a thread when
subjected to a tensile force. It is based upon a
diameter which is the mean of the pitch (or
effective) and the minor (or root) diameters of the
thread. The use of this diameter stems from the work
of E. M. Slaughter in the 1930's. He completed
carefully controlled tests using various sizes of
standard threads and compared their strength with
machined bars made from the same bar of material. He
found that this mean diameter give results that
agreed with the tensile test results to within about
3%. The error on the minor and pitch diameters was
about 15%. Tests completed subsequent to these by
other investigators have also shown that the stress
diameter is a reasonable approximation to a threads
tensile strength. (Referance: 'Tests on Thread
Sections Show Exact Strengthening Effect of
Threads.' by E. M. Slaughter, Metal Progress, vol
23, March 1933 pp. 18-20)
Stress Relieve:
Heating to a suitable temperature, holding long
enough to reduce residual stresses and then colling
to minimize the development of new residual
stresses.
Stripper Bolt:
Common term for socket shoulder bolt
Stove Bolt:
Old Term commonly referring to machine screw and nut
combination
Stove Head:
Old term for Truss Head
Strain:
The unit of change in the size or shape of a body
due to force. Also known as nominal strain.
Strain Hardened:
To increase hardness and strength by (a) cold
working of raw material by a steel mill or (b) cold
forming by a fastener manufacturer can sharply
increase tensile strength and hardness, so that
ordinary material from a steel mill may often be
used. However, fasteners that are milled from bar
will decrease in strength and hardness, so that raw
material would need to be strain hardened by a steel
mill before milling fasteners.
Stress:
The intensity of the internally distributed forces
or components of forces that resist a change in the
volume or shape of a material that is or has been
subjected to external forces. Stress is expressed in
force per unit area and is calculated on the basis
of the original dimensions of the cross section of
the specimen. Stress can be either direct (tension
or compression) or shear.
Stress Corrosion:
Occurs when corrosion causes a highly stressed part
(one that is pushed to its maximum tensile strength)
to crack. Except for heat treated 400 series
stainless, stress corrosion does not normally apply
to austenitic stainless, brass, or bronze, since
these metals are relatively ductile and not normally
used for high tensile operations.
Stress Ratio, A or R:
The algebraic ratio of two specified stress values
in a stress cycle. Two commonly used stress ratios
are: (1) the ratio of the alternating stress
amplitude to the mean stress. A = Sa/Sm and (2) the
ratio of the minimum stress to the maximum stress. R
=Smin/Smax.
Stress-Relief Cracking:
Also called postweld heat treatment cracking,
stress-relief cracking occurs when susceptible
alloys are suhjected to thermal stress relief after
welding to reduce residual stresses and improve
toughness. Stress-relief cracking occurs only in
metals that can precipitation-harden during such
elevated-temperature exposure; it usually occurs at
stress raisers, is intergranular in nature, and is
generally observed in the coarse-grained region of
the weld heat-affected zone. See also cold
cracking, hot cracking, and lamellar tearing.
Stress Relieving:
Heat treatment carried out in steel to reduce
internal stresses.
Stripper Bolt:
Discarded term for a shoulder screw.
Structure Machine Screws:
A Flat Head Machine Screw (AN509C) with one included
angle approximately 100 degrees. Usually made in
slotted and recessed head types. With a "grip" or
unthreaded body at the head.
Structural Bolt:
A structural bolt is a heavy hexagon head bolt
having a controlled thread length intended for use
in structural connections and assembly of such
structures as buildings and bridges. The controlled
thread length is to enable the thread to stop before
the joint ply interface to improve the fastener's
direct shear performance.This term is used in civil
and structural engineering but is not frequently
used in mechanical engineering.
Stud:
A threaded rod. It may be threaded at both ends or
continuous.
Subsurface Corrosion:
Formation of isolated particles of corrosion
products beneath a metal surface. This results from
the preferential reactions of certain alloy
constituents to inward diffusion of oxygen,
nitrogen, or sulfur.
Sulfide Stress Cracking:
Brittle failure by cracking under the combined
action of tensile stress and corrosion in the
presence of water and hydrogen sulfide. See also
environmental cracking.
Sulfur:
A non-metallic substance found in large quantities
by itself or combined with other elements to form
sulfates and sulfides. It improves machineability,
and helps cool material and prevent galling, but its
presence lowers the corrosion resistance of
stainless.
Super Passivation:
A term used for electro-polishing stainless
Symmetrical Thread:
A symmetrical thread is one which has both flanks of
the thread profile inclined are the same angle.
T-Head: The
T-head is an oblong shaped head, having a rounded
top surface, flat sides, and a flat bearing surface.
Tap:
(v) To cut threads in a hole with a rotating tool
called a "tap", having threads on it and fluted to
give cutting edges.
Tap Bolt:
A fully threaded hexagon head bolt.
Tap End Stud:
A double-end stud having each end threaded for a
different class of fit. The tap end has a Class 5
fit to produce an interference fit in a tapped hole
for semi-permanent assembly. The nut end is threaded
Class 2A for assembly with a standard nut.
Taper of Head:
In flat bearing surface fasteners, the taper of a
head or nut is the angle between a side and the
axis.
Tapped Hole:
A threaded hole in a part.
Taper Pin:
A pin that tapers from the larger end to a smaller
end at the rate of 1/4" per foot. The taper pin aids
in hole alignment.
Tapping Screw:
A screw which is threaded to the head and designed
to form or tap its mating thread in one or more of
the parts to be assembled, of various types as
follows:
Tapping Screw, Type A:
A thread-forming type of tapping screw having a
gimlet point and a thread of relatively coarse pitch
and special form, used in punched, or nested holes
in metal sheets or in treated plywood or special
asbestos compositions.
Tapping Screw, Type B:
A thread-forming type of tapping screw, having a
blunt point with tapered threads of moderate pitch,
used with punched, drilled or nested holes.
Tapping Screw, Type AB:
A thread-forming screw with the gimlet point of the
type A and the thread of the Type B. Uncommon in
stainless.
Tapping Screw, Type C:
A thread-forming type of tapping screw having a
blunt point with tapered threads at the end, having
UNC or UNF threads and designed for fastening metal
sheets. IFI no longer recommends this type.
Tapping Screw, Type D:
Also designated "type 1". A thread-cutting type of
tapping screw having the same thread as type C but
provided with a fluted end produced at thread
rolling or a milled slot (or slots) produced after
thread rolling.
Tapping Screw, Type F:
A thread-cutting type of tapping screw having the
same thread form as type C but provided with a
multiple flute tapered end to facilitate tapping.
Tapping Screw, Type BP:
A thread-cutting type of tapping screw having the
same thread form as type B but provided with a
multiple fluted tapered end to facilitate tapping.
Tapping Screw, Type G:
A thread-cutting type of tapping screw having the
same thread form as type C but provided with a slot
across the end to facilitate tapping in hard
materials or deep holes.
Tapping Screw, Type BT: Also designated "type 25". A thread cutting type of
tapping screw having the same thread as a type B but
provided with a slot in the end to facilitate
tapping in plastics.
Tapping Screw, Type T:
Also designated "type 23". A thread cutting type of
tapping screw having the same thread as a type C but
provided with a slotted tapered end.
Tarnish:
Surface discoloration of a metal caused by formation
of a thin film of corrosion product.
"Tee" Head Bolt:
Bolt whose head slightly curves in the shape of a
"T". Hence the name "TEE" Head Bolt.
Tek:
A self drilling screw. TEK is a registered
trademarked to ITW Buildex and Illinois Tool Works,
Inc. The term is widely used in the industry to
describe any self drilling screw and has become a
generic term much like Coke is to the soft drink
industry. If brand susbstitution is unacceptable,
you should specify Buildex parts only
Temper:
(1) In heat treatment, to reheat hardened steel or
hardened cast iron to some temperature below the
eutectoid temperature for the purpose of decreasing
hardness and increasing toughness. The process is
also sometimes applied to normalized steel. (2) In
tool steels, temper is sometimes inadvisably used to
denote carbon content. (3) In nonferrous alloys and
in some ferrous; alloys (steels that cannot be
hardened by heat treatment), the hardness and
strength produced by mechanical or thermal
treatment, or both, and characterized by a certain
structure, mechanical properties. Or reduction of
area during cold working.
Temper Color:
A thin, tightly adhering oxide skin (only a few
molecules thick) that forms when steel is tempered
at a low temperature, or for a short time, in air or
a mildly oxidizing atmosphere. The color, which
ranges from straw to blue depending on the thickness
of the oxide skin, varies with both tempering time
and temperature.
Tempered Martensite Embrittlement:
Embrittlement of ultrahigh-strength steels caused by
tempering in the temperature range of 205 to 400 ºC
(400 to 750 ºF); also called 350 ºC or 500 ºF
embrittlement. Tempered martensite embrittlement is
thought to result from the combined effects of
cementite precipitation on prior-austenite grain
boundaries or interlath boundaries and the
segregation of impurities at prior-austenite grain
boundaries.
Temper Embrittlement:
Embrittlement of alloy steels caused by holding
within or cooling slowly through a temperature range
just below the transformation range. Embrittlement
is the result of the segregation at grain boundaries
of impurities such as arsenic, antimony, phosphorus,
and tin; it is usually manifested as an upward shift
in ductile-to-brittle transition temperature. Temper
embrittlement can be reversed by retempering above
the critical temperature range, then cooling
rapidly.
Tempering:
Reheating a quench-hardened or normalized ferrous
alloy to a temperature below the transformation
range and then cooling at any rate desired.
Tensile strength:
The maximum load in tension (pulling apart or
shearing) which a material can withstand before
breaking or fracturing. Also known as the ultimate
tensile strength (UTS) or maximum strength.
Tension: The force or load that produces elongation.
Tension Washers:
A general name given to spring washers, curved
washers, Belleville washers and disc springs. This
type of washer provides a relatively low stiffness
(compared to the joint stiffness) and can be used to
act as a spring take-up with a bolt to prevent
movement between parts.
Terminal Stud:
A threaded and collared pin having a plain
cylindrical section, used as a contact terminal on
electrical appliances. Some types are headed instead
of collared
Therdermal Electromotive Force:
The electromotive force generated in a circuit
containing two dissimilar metals when one junction
is at a temperature different from that of the
other. see also thermocouple.
Thermal Embrittlement:
Intergranular fracture of maraging steels with
decreased toughness resulting from improper
processing after hot working. Thermal embrittlement
occurs upon heating above l095 ºC (2000 ºF ) and
then slow cooling through the temperature range of
815 to 980 ºC (1300 to l800 ºF), and has been
attributed to precipitation of titanium carbides and
titanium carbonitrides at austenite grain boundaries
during cooling through the critical temperature
range.
Thermal Spraying:
A group of coating or welding processes in which
finely divided metallic or nonmetallic materials are
deposited in a molten or semimolten condition to
form a coating. The coating material may be in the
form of powder, ceramic rod, wire, or molten
materials. See also flame spraying and plasma
spraying.
Thermocouple:
A device for measuring temperatures, consisting of
lengths of two dissimilar metals or alloys that are
electrically joined at one end and connected to a
voltage-measuring instrument at the other end. When
one junction is hotter than the other, a thermal
electromotive force is produced that is roughly
proportional to the difference in temperature
between the hot and cold junctions.
Thermogalvanic Corrosion:
Corrosion resulting from an electrochemical cell
caused by a thermal gradient.
Thickness of Thread:
The distance between the flanks of the thread
measured at a specified position and parallel to the
axis.
Threads:
Class 1 threads are a loose tolerance. Class 2
threads comprise 90% of stainless fasteners and are
normal commercial tolerance. Class 3 threads have a
stricter tolerance and tighter fit such as socket
cap and set screws. No definite relationship exists
between tensile strength and tightness or looseness
of fit. The symbol “A” added to threads, such as 2A,
means external threads (screws), and “B” means
internal (nuts).
With the exception of 10/32 diameter, which is
extremely popular, coarse thread comprises 90-95% of
hex head cap screws and hex nuts sold in 18-8
stainless, and perhaps 98% of other stainless items
including machine screws and socket products. Coarse
threads are deeper than fine threads with fewer
threads per inch, so coarse threads may have greater
protection against thread stripping, better tap in
brittle materials, and better fatigue resistance,
while fine threads may have better fit in
thin-walled materials, higher torque strength, and
increased tightness during vibration.
Threadlocker:
Can be a term used for a number of vibration
resistant products but is now usually reserved for
threadlocking adhesives. Specifically, a liquid
anaerobic adhesive applied to nut or bolt thread,
once hardened it fills the inner spaces between the
threads to produce a solid plastic of a known shear
strength.
Thread Crest:
The top part of the thread. For external threads,
the crest is the region of the thread which is on
it's outer surface, for internal threads it is the
region which forms the inner diameter.
Thread Flank:
The thread flanks join the thread roots to the
crest.
Thread Height:
This is the distance between the minor and major
diameters of the thread measured radially.
Thread Length:
Length the portion of the fastener with threads.
Thread Milling:
A machining process whereby thread is formed on a
surface by generating with a rotating toothed
cutter. Each tooth takes an individual chip.
Thread Rolling:
A cold-forging process whereby screw threads are
formed by displacement of metal as opposed to
cutting. The process is usually used for producing
external threads and is seldom practical for small
quantities.
Thread Rolling Screw:
A coarse threaded trilobular screw self tapping
screw with thread rolling action, suitable for
ductile material's.
Thread Root:
The thread root is the bottom of the thread, on
external threads the roots are usually rounded so
that fatigue performance is improved.
Thread Runout:
The portion at the end of a threaded shank which is
not cut or rolled to full depth, but which provides
a transition between full depth threads and the
fastener shank or head.
Thread Series:
Groups of diameter-pitch combinations distinguished
from each other by the number of threads per inch
applied to a specific diameter.
Threads Per Inch:
The reciprocal of the lead in inches.
Threshold Stress:
Threshold stress for stress-corrosion-cracking. The
critical gross section stress at the onset of
stress-corrosion cracking under specified
conditions.
Thumb Screw:
A screw with a flattened or roughened head to be
turned with thumb and finger.
Tin:
A malleable and ductile metal which increases
strength, hardness and corrosion resistance against
salt water when added to brass alloys.
Tinners' Rivet:
A small rivet having a head of the same form as a
flat head rivet but larger in diameter, used in
sheet metal work.
Titanium:
A silvery gray metal with high corrosion resistance
against salt waters, chlorides, and many acids. It
is strong, though lightweight, and very expensive.
Tolerance:
The total permissible variation of a size. The
tolerance is the difference between the limits of
size.
Tolerance Class:
A combination of tolerance grade and a fundamental
deviation which is given to an internal or external
thread. A tolerance class for an internal thread
when combined with the tolerance class for an
external thread gives the class of fit for the
mating threads.
Tolerance Grade:
The difference between maximum and minimum metal
conditions for a tolerance applied to a screw
thread. For metric threads the tolerance grade is
given a number.
Tolerance Limit:
The variation, positive or negative, by which a size
is permitted to depart from the design size.
Tooth Lockwasher:
A washer, usually a thin disk with prongs or
projections, which is elastically deformed when
assembled with a threaded fastener, so that the
prongs, on which the pressure is localized, resist
loosening of the fastener.
Torque:
Torque is the force used in twisting, such as
tightening a fastener. Torsion strength is the
amount of force needed to twist a fastener apart.
Both measures consider the amount of pressure
applied to the fastener and the length of the wrench
used in the application.
Torque Wrench:
A manual wrench which incorporates a gauge or other
method to indicate the amount of torque transferred
to the nut or bolt.
Torsion:
A twisting deformation of a solid body about an axis
in which lines that were initially parallel to the
axis become helices.
Torsional Stress:
The shear stress on a transverse cross section
resulting from u twisting action.
Total Thread:
Includes the complete or effective thread and the
incomplete thread.
Transference:
The movement of ions through the electrolyte
associated with the passage of the electric current.
Also called transport or migration.
Transgranular Cacking: Cracking or fracturing that occurs through or across
a crystal or grain. Also called transcrystalline
cracking. Contrast with intergranular cracking.
Transpassive State:
(1) State of anodically passivated metal
characterized by a considerable increase of the
corrosion current, in the; absence of pitting, when
the potential is increased. (2) The noble region of
potential where an electrode exhibits at higher than
passive current density.
Transition Temperature:
(1) An arbitrarily defined temperature that lies
within the temperature range in which metal fracture
characteristics (as usually determined by tests of
notched specimens) change rapidly, such as from
primarily fibrous (shear) to primarily crystalline
(cleavage) fracture. (2) Sometimes used to denote an
arbitrarily defined temperature within a range in
which the ductility changes rapidly with
temperature.
Trim Heads:
Similar to the 82 degree flat and oval head machine
screws except that the size of head for a given size
screw is one or two sizes smaller than the regular
flat and oval sizes.
Truss Head:
Low rounded top surface with a flat bearing surface.
Toughness:
A fastener’s capacity to accept various impacts and
shocks.
Tuberculation:
The formation of localized corrosion products
scattered over the surface in the form of knoblike
mounds called tubercles.
Tubular Rivet:
A small rivet having a coaxial cylindrical hole in
the headless end, designed for securing by splaying
the end.
Tumble:
To clean, smooth, or polish in a rotating barrel or
drum by friction with each other, assisted by added
mediums, as scraps, balls, sawdust, etc.
Turn:
To machine on a lathe.
Turnbuckle:
A coupling, threaded right and left or swiveled on
one end, for adjustably connecting two rods.
U-Bolt:
A "bent bolt" having threads at both ends of the rod
and the rod bent at the middle to a semicircle or to
two right angles, used for clamping.
UN, UNR:
Indicates “unified” screw threads to “inch”
dimensions used in the U.S. as distinquished from
metric dimensions.
UNC:
The coarse thread series UNC/UNRC is the most
commonly used thread system used in the majority of
screws, bolts, and nuts. It is used for producing
threads in low strength materials such as cast iron,
mild steel, and softer copper alloys, aluminum etc.
The coarse thread is also used for rapid assembly or
disassembly.
UNF:
The fine thread UNF is used for applications that
require a higher tensile strength than the coarse
thread series and where a thin wall is required.
UNJ:
A type of threads originating around the 1950’s with
a more rounded fit in order to prevent cracks,
reduce loosening due to vibration and slightly
increase strength. Possessing a tighter fit, UNJ
thread depth is smaller that the usual UN standards
with the minor diameter of external threads on
screws and internal threads on nuts both increasing.
UNJ is used in critical applications by the
aerospace and automotive industries.
Undercut Head:
For short lengths of flat and oval head machine
screws, the heads are undercut to 70 per cent of
normal side height to afford greater length of
thread on the screws.
Under-size Body:
The reduced body of a bolt or screw, the diameter of
which may range from below the pitch diameter to the
minimum major diameter of the thread. Such a body
diameter is found on some bolts or screws having
rolled threads.
Unified Thread Standards:
The basic American standards for fastening screw
threads as agreed upon by standard bodies of Canada,
the United Kingdom, and the United States. They are
a complete and integrated system of threads for
fastening purposes. Their outstanding characteristic
is general interchangeability of threads achieved
through the standardization of thread form,
diameter-pitch combinations, and limits of size.
Upsetting:
1. A metal working operation similar to forging. 2.
The process of axial flow under axial compression of
metal, as in forming heads on rivets by flattening
the end of wire.
Washer Face:
A circular boss turned or otherwise produced on the
bearing surface of a bolt head or nut to relieve the
corners.
Wedge Anchor:
The wedge anchor is a high grade, fully threaded
stud type anchor
Weld Screw:
Projection welding applied to screws offer a means
of providing attached threated members in sheet
metal construction. Welding lugs on the head of the
screw reduce the amount of current required for
surface welding and provide fusion of metal at
predetermined points.
Welding Stud:
A "drive screw" having a flat fillister head, used
as an anchorage for welding.
Whitworth Thread:
A screw thread, also known as the British Standard
Whitworth (B.S.W.), used principally in Great
Britain.
Wing Nut:
One-piece, round threaded nuts with wing lugs for
ease of manual assembly. Particularly suited to
applications where frequent removal and replacement
or adjustment are required.
Wing Screws: Special screws with projection heads. Widely used in
industry and home where a finger tightened screw is
needed for frequent adjustments or for knock-down
assembly applications. This piece is produced by
pressing, forming, machining, welding or die
casting. (Also available as 2 piece wing nut and
studs, peened or welded together.
Wood Screw:
A metal screw having a driver head, a gimlet
point, and a sharp- crested, coarse pitch thread,
for insertion in wood or resilient materials. It
produces its own mating thread.
Woodruff Key:
A semi-circular or half-round piece, resting in a
circular groove cut in a shaft. Sometimes referred
to as a half moon key. Largely used in machine
building.
Work Hardening:
Hardening that takes place through grain alignment
when a metal is bent, rolled or hammered at room
temperature, Not all metals work harden
Wrench Head:
A head on a fastener designed for driving or holding
by means of an externally applied wrench to the
sides of the head.
Yield:
The resistance to a load pulling on the middle of a
fastener until the fastener shows permanent
deformation.
Yield Controlled Tightening:
A fastener tightening method which allows a fastener
to be tightened to yield. The angle of rotation of
the fastener is measured relative to the applied
torque, yield being assessed when the slope of the
relationship changes to below a certain value.
Sometimes called joint controlled tightening.
Yield Point:
The stress necessary to produce an elongation under
load of 0.50 per cent of the specimen's original
length. Expressed as psi. The load at which a sudden
drop in the flow curve occurs is called the upper
yield point. The constant load shown on the flow
curve is the lower yield point.
Yield Strength: The stress at the yield point. The stress at which a
material exhibits a specified limiting deviation
from the proportionality of stress to strain. The
lowest stress at which a material undergoes plastic
deformation. Below this stress, the material is
elastic; above it, the material is viscous. Often
defined as the stress needed to produce a specified
amount of plastic deformation (usually a 0.2% change
in length). Or - The maximum load at which a
material exhibits a specific permanent deformation.
Zinc Plating:
The application of a zinc coating
Zinc Electroplating:
Zinc electroplating is a common way to protect
threaded fasteners from the effects of corrosion.
Zinc electroplating can be completed in acid
chloride, alkaline or cyanide baths. Supplemental
coatings are frequently applied to zinc
electroplating. These coatings, such as zinc
phosphate or chromate conversion, provide a
protective passivation layer on the zinc which
assists in reducing the corrosion rate.
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Page 2 (G-N), Page 3 (N-Z)
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