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Page 1 (A-F),
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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.
“18-8” :
300
series stainless steel having approximately (not
exactly) 18% chromium and 8% nickel. The term “18-8”
is used interchangeably to characterize fasteners
made of 302, 302HQ, 303, 304, 305, 384, XM7, and
other variables of these grades with close chemical
compositions. There is little overall difference in
corrosion resistance among the 18-8 types, but
slight differences in chemical composition do make
certain grades more resistant than others against
particular chemicals or atmospheres. “18-8” has
superior corrosion resistance to 400 series
stainless, is generally non-magnetic, and is
hardenable only by cold working.
"A" Sheet Metal Screws: Sheet metal screws
with (a) sharp-pointed ends; and (b) fewer threads
per inch than type AB screws; and (c) deeper threads
with better gripping power than type AB. The
Industrial Fasteners Institute incorrectly labels
type A an “obsolete” thread though it is universally
preferred in 18-8 stainless over type AB, especially
by the marine industry.
"AB" Sheet Metal Screws: Sheet metal screws
with pointed ends similar to type-A screws and
thread dimensions similar to type-B. Type AB screws
are seldom used in stainless.
Acme Thread: A screw thread having a 29
degree included angle.
Acorn Nut: A blind tapped hex nut with an
acorn shaped (domed) top. Provides sealing for
projecting threaded parts. Sometimes referred to as
a cap nut although generally acorn nuts are more
peaked while cap nuts are more rounded on the tops.
Age Harden: To use modified heat treatments
at various temperatures over a period of time to
harden and strengthen a fastener.
Aircraft Quality:
Aircraft quality as applied to fasteners implies
that they are to be used in highly stressed
applications and that they are to be produced under
closely controlled, special, and, in most cases,
restricted methods of manufacture and inspection.
Air Force & Navy Aeronautical Standard Drawings:
Dimensional standards for aircraft fasteners
developed by the Aeronautical Standards Group . All
drawings are prefixed by "AN" .
Allen Screw: An older term for socket recess
drive - still popular in the automotive industry
Allowance: An intentional clearance between
internal or external thread and the design form of
the thread when the thread form is on it's maximum
metal condition. Not all classes of fit have an
allowance. For metric threads the allowance is
called the fundamental deviation.
Alloy Steel: A mixture (or alloy) of ordinary
steel added to other metals besides carbon with the
specific purpose of attaining certain
characteristics such as higher strength. A few
exceptions to this definition exist, however, so
that a chromium content above 4% is not considered
alloy steel and above 12% is considered stainless
steel.
Alloy Steels: Steels alloyed with molybdenum,
nickel and chromium (AISI 4037,4130, 8630) are best
where high strength is required. These steels have
good cold-forming properties in the annealed
condition. Can be heat treated for the best
combination of strength, toughness and shock
resistance.
Aluminum: The most abundant metal in the
earth, aluminum is blueish and silvery-white, very
light, malleable, and ductile with high heat and
electrical conductivity. It is non-magnetic and
one-third the weight of steel with good corrosion
resistance against certain chemicals and acids but
weak resistance against other elements such as sea
water.
Aluminum Alloys: Good cold-forming
characteristics. Many aluminums can be used (2024,
3003, MM, MM, 6061, 7075), and where secondary
machining is required (2011). Aluminum is corrosion
resistant and some can be heat treated.
Aluminum Irridite: A chemical conversion process used on aluminum and
various aluminum alloys. It is performed on these
metals to give them added corrosion protection when
a coating is not employed. It is also used to
improve the adhesion of paints and finishes.
American Standards: Dimensional standards for fasteners, etc., developed
by the American Society of Mechanical Engineers.
(ASME)
AMS:
Aeronautical Material Specifications are material
and process specifications for aircraft components
conforming to established engineering and
metallurgical practices in the aircraft industries.
They are developed by the SAE aeronautics committee.
All specifications are prefixed by "AMS".
AN:
Dimensional standards for aircraft fasteners
developed by the Aeronautical Standards Group. All
drawings are prefixed by "AN". Stands for Air Force
- Navy. Organization
Anaerobic Adhesive: An adhesive which hardens in the absence of air,
such adhesives are often used as a thread locking
medium.
Anneal: To heat metal in order to lower its hardness. The
term anneal refers to the heat treatment given all
300 series stainless and most 400 series stainless
by the steel mill after the raw material has been
completed but before fasteners are manufactured.
Anneal also refers to the heat treatment given 400
series stainless fasteners after their manufacture
(also called hardening and tempering) to lower
hardness and increase toughness. For example,
fasteners of 410 stainless may score over 200,000
psi after manufacture and be too brittle. By
annealing at 1000 degrees F., tensile strength would
reduce to 125,000-150,000 psi, while annealing the
same material to 500 degrees F. would bring tensile
to 160,000-190,000 psi.
Angle of Head:
In countersunk heads, the included angles of the
conical underportion or bearing surface, usually 82
or 100 degrees.
Angle Controlled Tightening:
A tightening procedure in which a fastener is first
tightened by a pre-selected torque (called the snug
torque) so that the clamped surfaces are pulled
together, and then is further tightened by giving
the nut an additional measured rotation. Frequently
bolts are tightened beyond their yield point by this
method in order to ensure that a precise preload is
achieved. Bolts of short length can be elongated too
much by this method also the bolt material must be
sufficiently ductile to cater for the plastic
deformation involved. Because of the bolt being
tightened beyond yield, its re-use is limited.
Anti-Friction Coating: AF coatings are dry lubricants consisting of
suspensions of solid lubricants, such as graphite,
PTFE or molydbenum disulphide of small particle size
in a binder. Such coatings can be applied to
fastener threads to replace metallic coatings such
as zinc and cadmium and offer maintenance free
permanent lubrication. By careful selection of the
lubricants AF coatings can be designed to meet
specific applications. The coatings are permanently
bonded to the metal surface and provide a
lubricating film preventing direct metal to metal
contact.
Anti-Seize Compound: An anti-seize compound is used on the threads of
fasteners in some applications. The purpose of the
compound depends upon the application. It can
prevent galling of mating surfaces - such compounds
are frequently used with stainless steel fasteners
to prevent this effect from occurring. In some
applications it is used to improve corrosion
resistance to allow the parts to be subsequently dis-assembled
Thirdly, it can provide a barrier to water
penetration since the threads are sealed by use of
the compound.
ANSI: Stands for American National Standards
Institute.
ASME: Stands for American Society of Mechanical
Engineers.
ASTM: Standards developed by the American Society for
Testing and Materials.
ASTM 193-194: ASTM 193 are chemical and physical specifications
for hex head cap screws, studs, and bolts made of
steel and stainless steel. ASTM 194 refers to nuts.
The commonly used stainless is called grade 8,
referring to 304 material to certain specifications,
and grade 8M referring to 316 material. The major
differences between ASTM and commercial stainless
fasteners are: (a) 304 material must be used for
manufacturing grade 8, not simply 18-8; (b) ASTM
generally refers to heavy hex heads and heavy nuts,
though semi-finished hex heads and finished nuts may
be supplied with the permission of the buyer; (c)
cold formed material will require carbide solution
treatment or annealing to reduce hardness to meet
ASTM requirements.
Austenitic: Refers to 300 series stainless, the most popular of
the stainless alloys accounting for 85% - 90% of
stainless fasteners sold. Named for Sir Robert
Williams Austen, an English metallurgist, austenitic
stainless is a crystal structure formed by heating
steel, chromium, and nickel to a high temperature
where it forms the characteristics of 300 series
stainless steel. An “AUSTENITE” is a molecular
structure where 8 atoms of iron surround one atom of
carbon, thus limiting the corrosive effects of the
carbon. Austenitic fasteners have the highest level
of corrosion resistance in the stainless family,
cannot be hardened by heat treatment, and are
non-magnetic for practical purposes.
The most popular of austenitic grades is known
generically as “18-8 stainless” and includes grades
302, 302HQ, 303, 304, 305, and XM-7. Typical
industries using 18-8 fasteners include: food,
dairy, wine chemical, pulp and paper,
pharmaceutical, boating, swimming pool, pollution
control, electronic, medical and hospital equipment,
computer, textile.
Type 316 stainless has added nickel and especially
molybdenum. The molybdenum (called moly) sharply
increases corrosion resistance to chlorides and
sulfates, including various sulfurous acids in the
pulp industry. It has superior tensile strength at
high temperatures compared to 18-8. Besides pulp and
paper, typical industries using 316 are:
photographic and other chemicals, ink, textile,
bleach, rubber.
Exotic metals in the 300 series include 309, 310,
317, 321, and 347. With superior corrosion
resistance at elevated temperatures, these metals
are used for furnace parts, high temperature
containers and processing equipment, aircraft parts
such as collector rings, exhaust systems, and
equipment for very corrosive compounds of sulfuric,
nitric, citric, and lactic acids.
Axis:
The line passing through the center of an object
about which it could rotate - a point of reference
Axis of Thread:
The axis of a thread is coicident with the axis of
its pitch cylinder/cone.
“B” Sheet Metal Screw:
Type-B indicates a blunt point with more threads per
inch and smaller thread depth than type-A screws.
Barrel Nut: An internally threaded screw having a slotted head.
Basic Thread Profile:
This is the theoretical profile of external and
internal threads with no manufacturing tolerance
applied.
Bearing Stress:
The surface pressure acting on a joint face directly
as a result of the force applied by a fastener.
Bearing Surface: The part of a fastener such as the washer face of a
nut or under the head of a machine screw that
actually comes in contact with the part it fastens.
Bent Bolt:
A cylindrical rod having a thread at one end and the
other end bent to some desired conformation; also a
bent cylindrical rod having threads at both ends.
Note: Bent Bolts are available from K-J Fasteners,
Inc. in Cleveland, Ohio. They can be reached at Toll
Free at
1-888-834-LION (5466), Click here to visit
www.kjfasteners.com.
Bevel:
A surface not at right angles to the rest of the
piece.
Binding Head:
Rounded top surface and slightly tapered sides. The
bearing surface is flat with annular undercut
optional.
Blind Rivet: A rivet designed for use where only one side of the
work is accessible.
Blunt Start:
The removal of the partial thread at the entering
end of thread.
Body of Bolt or Screw: Also designated grip. The blank portion of the bolt
or screw which is between the thread and the head.
Bolt:
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. Case
made US Customs Department "Distinguishing Bolts
from Screws"
Bolt Blank:
A headed rod or bar intended for a subsequent
threading operation.
Bolt End:
A headless rod threaded at one end and assembled
with a square nut, designed to be welded or
otherwise fastened to a part or structure.
Brass:
The most common alloy of copper, brass is basically
two-thirds copper, one-third zinc. It is
non-magnetic with good strength and toughness, high
electrical conductivity, and an attractive lustrous
finish. It has good corrosion resistance but not in
salt water. Brass is commonly used by the electrical
and communications industries, builders hardware,
and some marine applications.
Breakaway Torque: The torque necessary to put into reverse rotation a
bolt that has not been tightened.
Breakloose Torque:
The torque required to effect reverse rotation when
a pre-stressed threaded assembly is loosened.
Brinell Hardness Test: A method of determining the hardness of metallic
materials by applying a known load to the surface of
the material through a hardened steel ball of known
diameter. The diameter (or depth) of the resulting
impression in the metal is measured. The Brinell
hardness number is taken as a quotient of the
applied load divided by the area of the surface
impression which is assumed to be spherical.
BSF British Standard Fine:
A thread form based upon the British Standard
Whitworth form but with a finer thread (more threads
per inch for a given diameter). This thread form was
first introduced in 1908, the thread form is
specified in BS 84: 1956.
BSW British Standard Whitworth: A thread form developed by Sir Joseph Whitworth in
1841. The thread form has rounded roots and crests,
the thread form is specified in BS 84: 1956. This
thread form was superceded by first the Unified
thread in 1948 and then the metric thread form.
Broaching:
A generating process whereby metal is removed with a
multiple-point tool, usually a bar, with tooth
height increasing from the starting end. When the
broach is pulled or pushed through or over the work,
each tooth removes a clip of uniform thickness, in
contrast to a milling cutting tooth which removes a
wedge-shaped chip.
Button Die: Small adjustable dies for screw machines and similar
work, supported in a ring holder.
Burnish: To smooth or polish by a rolling or sliding tool
under pressure.
Cadmium Electroplating:
Coating of threaded fasteners with cadmium can
provide the parts with excellent corrosion
resistance. The appearance of the coating is bright
silver or yellow if subsequently passivated. The
friction values associated with this coating are
also comparatively low. A chromate conversion
coating is frequently applied to the surface to
improve corrosion resistance. Cadmium is not now
frequently used because of the environmental and
worker health problems associated with the coating
process and should not be used in applications above
250C or when contact with food is possible.
Camout:
A mechanical reaction to the applied torque that has
a tendency to disengage the bit from the fastener.
Cap Nut:
A blind tapped hex nut with an acorn-shaped top.
Provides sealing for projecting thread parts.
Sometimes referred to as an acorn nut although
generally acorn nuts are more peaked while cap nuts
are more rounded on the tops.
Cap Screws:
Term used to describe hexagon head, slotted head,
square head and socket head cap screws.
Captive Screws: Where the shank above the threaded portion is
undercut lower than the threaded portion.
Carbide Precipitation: Carbon that breaks loose from its bond within the
stainless solution when material is heated between
800 - 1400 degrees F. Under severe corrosive
conditions, it can result in extra oxidation and
surface corrosion.
Carbide Tools: Tools with cutting points of tungsten, tantalum or
other alloys of sintered carbides.
Carbon:
Adds strength to stainless steel, but also lowers
corrosion resistance. The more carbon there is, the
more chromium must be added, because carbon offsets
17 times its own weight in chromium to form
carbides, thus reducing the chromium available for
resisting corrosion.
Carbon Steel:
Fine grain, fully-killed basic steel with no
alloying agent.
Low carbon steel range from .06-.1 8% carbon content
(AS 1006-1018) and have good ductility for cold
forming.
Medium carbon steel have .1 8-.50% carbon content (AJSI
1018, 1038, 1041). Stronger and less ductile, these
steels respond well to quench and temper.
High carbon steels .50% carbon and up (AISI
1066,1095). Difficult to cold form unless annealed.
High strength, can be heat treated.
Carriage Bolts:
A round or flat head bolt with a square neck to
prevent rotation. Used in wood assemblies.
Case Harden:
Hardening a ferrous alloy so that the outer portion
or case is made substantially harder than the inner
portion or core. Typical processes used for case
hardening are carburizing, cyaniding, carbonitriding,
nitriding, induction hardening, and flame hardening.
Casting: 1. A term applied to the act of pouring molten metal
into a mold. 2. The metal object produced by such
pouring.
Castle Nut: A hexagon nut having a cylindrical portion at the
end opposite to the bearing face, with opposed slots
in this portion which are parallel to the axis,
designed for insertion of a cotter to secure the nut
in place when used with a drilled fastener.
Cathode: The electrode of an electrolytic cell at which
reduction is the principal reaction. (Electrons How
toward the cathode in the external circuit.) Typical
cathodic processes are taking up electrons and being
discharged, oxygen being reduced. and the reduction
of an element or group of elements from a high Cl a
lower valence state. Contrast with anode.
Cathodic Corrosion:
Corrosion resulting from a cathodic condition of a
structure usually caused by the reaction of an
amphoteric metal with the alkaline products of
electrolysis.
Cathodic Disbondment: The destruction of adhesion between a coating and
its substrate by products of a cathodic reaction.
Cathodic Inhibitor: A chemical substance or mixture that prevents or
reduces the rate of the cathodic or reduction
reaction by physical, physico-chemical or chemical
action.
Cathodic Pickling: Electrolytic pickling in which the work is the
cathode.
Cathodic Polarization:
Polarization of the cathode; change of the electrode
potential in the active (negative) direction due to
current flow; a reduction from the initial potential
resulting from current flow effects at or near the
cathode surface. Potential becomes more active
(negative) because of cathodic polarization. See
also polarization.
Cathodic Protection: (1) Reduction of corrosion rate by shifting the
corrosion potential of the electrode toward a less
oxidizing potential by applying an external
electromotive force. (2) Partial or complete
protection of a metal from corrosion by making it a
cathode, using either a galvanic or an impressed
current. Contrast with anodic protection.
Cathodic Reaction:
Electrode reaction equivalent to a transfer of
negative charge from the electronic to the ionic
conductor. A cathodic reaction is a reduction
process. An example common in corrosion is: Ox + ne
s Red.
Catholyte:
The electrolyte adjacent to the cathode of an
electrolytic cell.
Centerless Grinding:
Grinding the outside or inside diameter of a round
piece not mounted on centers.
Chamfer:
(v) the tapering of the threads at the front end of
each land of a tap by cutting away and relieving the
crest of the first few teeth to distribute the
cutting action over several teeth. (n) A beveled
edge.
Chasing Threads:
Cutting screw threads by moving a tool along the
axis of the work to be threaded.
Chatter: Rough or unsatisfactory surfaces on work. It is
usually caused by a slight jumping of the tool away
from the work or of the work away from the tool.
Check Nut:
A double chamfered hexagon machine screw nut Class
3B fit. (AN 316).
Cheese Head:
Old term for fillister head.
Chip:
The metal removed by a tool.
Chromium:
A blue-white metal, chromium is the most important
element providing corrosion resistance in stainless
steel. By adding 12% chromium to ordinary steel,
stainless steel is formed. Chromium offsets the
corrosive effects of carbon found in steel and is
the primary factor in the ability of stainless to
form a passive film on its surface providing
corrosion resistance. Discovered in 1797 by
Vauquelin, who prepared the metal the next year,
chromium is a steel-gray, lustrous, hard metal that
takes a high polish. The principal ore is chromite,
which is found in Zimbabwe, Russia, Transvaal,
Turkey, Iran, Albania, Finland, Democratic Republic
of Madagascar, and the Philippines. The metal is
usually produced by reducing the oxide with
aluminum. Chromium is used to harden steel, to
manufacture stainless steel, and to form many useful
alloys.
Chrome Plating: A thin, shiny metallic surface layer of chromium
electrodeposited on other metals, typically nickel.
Chrome plating was first developed in 1856 by
Geuther by dipping a metal in a chromic acid bath.
By 1924, the method was perfected and widely used to
create a mirror-like finish. Chrome plating usually
has a thickness of 2 - 5 micrometers. It provides a
shiny surface that is resistant to corrosion, wear
and heat. Small air bubbles between the chrome
plating and the base metal can result in tiny black
corrosion pits.
Chuck:
Device for holding work in machine tools.
Clamping Force:
The compressive force which a fastener exerts on the
joint.
Class of Fit:
The Class of Fit is a measure of the degree of fit
between mating internal and external threads. Three
main Classes of Fit are defined for metric screw
threads : FINE: This has a tolerance class of 5H for
internal threads and 4h for external threads.
MEDIUM: This has a tolerance class of 6H for
internal threads and 6g for external threads.COARSE:
This has a tolerance class of 7H for internal
threads and 8g for external threads. For Unified
threads, a similar designation as for metric threads
is used. The thread classes used are 1A, 2A and 3A
for external threads and 1B, 2B and 3B for internal
threads.
Class of Thread:
Class of threads are distringuished from each other
by the amount of tolerance or tolerance and
allowance specified. Classes 1A, 2A, and 3A apply to
external threads, and Classes 1B, 2B and 3B apply to
internal threads.
Clevis:
U-shaped shackle for connecting a rod to a pin.
Clevis Pins:
A headed dowel pin with a drilled shank that accepts
a cotter pin. Used as a fastener where more than
temporary holding actions is required. (ASA B
5.20-1958).
Clinch Nut: A nut having a pilot which, after insertion in a
hole, is clinched or staked in place to prevent
rotation.
Coefficient of Friction:
A dimensionless number representing the ratio of the
friction force to normal force. Typically for
threaded connections it is about 0.16 but can vary
significantly depending upon the materials used and
whether a lubricant has been used.
Cold Forming/Cold heading/Cold Working: When fasteners are produced without heating or small
heat below the recrystallization temperature (so the
raw material bond of stainless remains unchanged) by
pressing metal wire against various dies at high
speed to form a fastener’s head or basic shape. Cold
working causes an increase in tensile strength and
hardness (known as work hardening) and a decrease in
ductility.
Cold Heading:
Forcing metal to flow cold into dies to form thicker
sections and more or less intricate shapes. The
operation is performed in specialized machines where
the metal, in the form of a wire or bar stock, may
be upset or headed in certain sections to a larger
size and, if desired, may be extruded in other
sections to a smaller diameter than the stock wire.
Cold heading
stock: A material produced under closely
controlled manufacturing and inspection methods so
as to be suitable for heading and to be free from
those defects causing fractures during heading.
Cold Swaging Process:
A method of reducing or forming steel or other
material while cold, by drawing to a point or
reducing the diameter, as may be required.
Cold Work: To deform metal stock by hammering, forming,
drawing, etc., while the metal is at ordinary room
temperature.
Commingling: A term used to describe the undesirable practice of
mixing fasteners from different batches that are the
same size and grade in the same container.
Companion Flanges: Shaft attached collars of 18-8 stainless steel into
which a threaded piece may be joinedd. Has standard
I.P.S. threads.
Comparator:
A device for inspecting screw threads and outlines
by comparing them with a greatly enlarged standard
chart.
Condition A:
Means that fasteners should be solution annealed.
Condition B:
Means strain hardened to meet certain minimum
tensile requirements.
Cone Point:
A point in the form of a cone, commonly having an
included angle of 90 degrees or 118 degrees when
applied to set screws.
Cone Proof Load:
This is an axial applied force applied to a nut when
it is seated on a cone shaped washer which has an
included angle of 120 degrees. Failure in this test
is usually due to the nut splitting. The intention
of the test is to introduce a nut dilation operation
which will assess the potential detrimental effects
of surface discontinuities. This type of test which
is sometimes applied to nuts which are intended for
high temperature service.
Conversion Coating: A coating consisting of a compound of the surface
metal, produced by chemical or electrochemical
treatments of the metal. Examples include chromate
coatings on zinc, cadmium, magnesium, and aluminum
and oxide and phosphate coatings on steel. See also
chromate treatment and phosphating.
Copper:
A reddish metal that is an excellent conductor of
heat and electricity. It is malleable, ductile, and
non-magnetic with low to average strength and good
corrosion resistance. Brass and silicon bronze,
composed mainly of copper, gain their strength from
the addition of other metals.
Copper Steel: When any minimum copper content is specified, the
steel is classed as copper steel. The copper is
added to enhance erosion resistance of the steel.
Corrosion:
Gradual chemical or electrochemical attack on a
metal by atmosphere, moisture or other agents. From
the Latin word "corrodere" which means to "gnaw
away". Corrosion is about metal atoms leaving the
security of the family crystal lattice and going
into a harsh aqueous world. For article on stainless
steel corrosion, click here..
Corrosion Rate: Corrosion effect on a metal per unit of time. The
type of corrosion rate used depends on the technical
.system and on the type of corrosion effect. Thus,
corrosion rate may be expressed as an increase in
corrosion depth per unit of time (penetration rate,
for example, mils/yr.) or the mass of metal turned
into corrosion products per unit area of surface per
unit of time (weight loss, for example, g/m-/yr.).
The corrosion effect may vary with time and may not
be the same at all points of the corroding surface.
Therefore. reports of corrosion rates should be
accompanied by information on the type, time
dependency, and location of the corrosion effect.
Corrosion Resistance:
Ability of a metal to withstand corrosion in a given
corrosion system.
Cotter Pin:
Used as a locking device in clevis pins, castellated
nuts and slotted nuts with drilled bolts. Ends
available in various types such as "extended mitre
end", etc.
Counterbore: (v) To enlarge a hole to a given depth. (n) 1. The
cylindrical enlargement of the end of a drilled or
bored hole. 2. A cutting tool for counterboring,
having a piloted end of the size of the drilled
hole.
Countersunk Head:
A head, the underside of which is beveled to fit a
flaring hole. The bearing surface of other types of
heads is generally perpendicular to the body axis.
Creep Strength:
A measure of the resistance of fasteners to stress
under elevated temperatures. At higher temperatures,
a fastener can change in dimension under the same
load, and that is called creep. Creep can cause the
loosening of fasteners as temperature increases.
Crest:
That surface of the thread which joins the flanks of
the thread and is farthest from the cylinder or cone
from which the thread projects.
Crest Clearance:
As in a thread assembly, the distance, measured
perpendicular to the axis, between the crest of a
thread and the root of its mating thread.
Crest Truncation of Thread:
The distance, measured perpendicular to the axis,
between the sharp root and the cylinder or cone
which bounds the root.
Crevice Corrosion:
Refers to joints and crevices in a fastener assembly
where lack of oxygen caused by limited space or by
surface grease prevents the passive film on
stainless from forming.
Cup Point:
A point in the form of a cone, commonly having an
included angle of 90 degrees, with a conical
depression in the end commonly having an included
angle of 118 degrees. The contact area is a circular
ridge which has considerable holding power with
slight penetration, applied to set screws generally.
Cut Threading:
Forming threads on a fastener by cutting away and
actually removing the unneeded metal.
Dacromet:
A high performance surface coating that can be
applied to fasteners. The coating consists of
passivated zinc flakes that is stoved onto the metal
surface. The coating can be coloured and eliminates
the risk of hydrogen embrittlement associated with
electroplated metal. DACROMET is a registered
trademark of Metal Coatings International, Inc. of
Chardon Ohio
Deburring:
The removal of chips or burrs by a secondary
operation such as grinding.
Decompression Point:
The point at which there is zero pressure at the
joint interface as a result of forces applied to the
joint. If the applied force is increased beyond the
decompression point, a gap will form at the
interface. Analytically, a criteria of joint failure
is often taken as when the applied force on the
joint reaches the decompression point. This is
because forces acting on the bolt(s) can
dramatically increase at this point. Loading beyond
this point can also result in fretting at the
interface that will lead to bolt tension loss that
will subsequently lower the decompression point.
This process can continue until bolt failure does
occur. The failure can be by fatigue or other
mechanism but the underlying cause was loading of
the joint beyond the decompression point. It is for
this reason that it is frequently taken as a failure
criteria in analysis work.
Deep Drawing:
Forming shaped articles or shells by forcing sheet
metal into a die.
Deoxidizing: (1) The removal of oxygen from molten metals by use
of suitable deoxidixers. (2) Sometimes refers to the
removal of undesirable elements other than oxygen by
the introduction of elements or compounds that
readily react with them. (3) In metal finishing, the
removal of oxide films from metal surfaces by
chemical or electrochemical reaction.
Descaling:
Removing the thick layer of oxides formed on some
metals at elevated temperatures.
Design Form of Thread: The design form of an internal or external thread is
the thread form in it's maximum metal condition. It
is the same as the basic thread profile except that
the thread roots are rounded. If either the internal
or external thread form exceeds the design form of
the thread profile then a potential interference
exists.
Die:
1. One of a pair of hardened metal blocks for
forming, impressing, or cutting out a desired shape.
2. (thread). A tool for cutting external threads.
Opposite of tap.
Die Casting:
A very accurate and smooth casting made by pouring a
molten alloy usually under pressure into a metal
mold or die.
Die Chaser:
The separate cutting tools used in die heads, which
actually cut the screw threads.
Dielectric Shield:
In a cathodic protection system, in electrically
nonconductive material, such as a coating, plastic
sheet or pipe that is placed between an anode and an
adjacent cathode to avoid current wastage and to
improve current distribution, usually on the
cathode.
Direct Tension Indicators:
(DTI's) is a term sometimes used to describe load
indicating washers. Projections on the face of the
washer (usually on the face abuting the bolt head or
nut) that deform under loading as the bolt is
tensioned. An indication of the tension in the bolt
can be made by measuring the gap between the washer
face and the nut or bolt head. The smaller the gap -
the greater the tension in the bolt.
Discontinuities:
A variety of small or large disfigurations in a
fastener such as pits (slight depressions on the
surface), tool marks, voids (small cracks), laps,
folds and seams (slightly bunched or folded material
at the corners of a fastener), and inclusions (a
slight non-metallic impurity in the metal). Minor
discontinuities are permissible in both commercial
fasteners and those made to various MS and other
specs.
Dog Point:
A cylindrical extension, or pilot, of diameter
smaller than the minor diameter of the thread,
commonly equal to about D/2 in length, with a
conical section between it and the thread; usually
used as a pilot in assembling or as the end of a set
screw projecting into a fairly deep hole or slot.
Double End Stud:
Threaded at both ends with standard Class 2A threads
to take nut assembly.
Dowel Pins:
Used as a holding pin with chamfered on one end.
Drilled headed dowel pin (clevis pin) used -
frequently removed fastener.
Dowel Screw:
Both ends have Gimlet points, threaded similar to a
Lag Bolt. The center section has a plain unthreaded
shoulder. Used in joining two wooden members such as
a leg to a table top.
Drawing:
Where raw material shaped like wire is pulled
through a die to reduce its diameter to that needed
for the particular fastener being manufactured.
Drill:
(v) To sink a hole with a drill, usually with a
twist drill. (n) A pointed cuttiniig tool rotated
under pressure.
Drilled Head or Shank:
Used in AN Bolts and Machine Screws, etc.
Drive Screw:
A piloted, multiple threaded screw with a large
helix angle, used for permanent applications. It
forms a mating thread as it is hammered or pressed
into a prepared hole.
Driver Recess:
A head, on a bolt or screw, designed for driving the
fastener by means of a tool other than a wrench,
such as a screw driver.
Drop Forging:
Forming metal, usually under impact, by compression
within dies designed to produce the required shape.
Ductility:
The ability of a metal to be deformed extensively
under tension load without rupture or fracture.
Ductility is expressed in terms of percent
elongation and percent reduction of area (e.g. drawn
into wire).
Dynamic Friction:
Resistance to relative movement of two bodies that
are already in motion.
Effective Diameter:
This is the diameter of an imaginary cylinder
coaxial with the thread, which has equal metal and
space widths. It is often referred to as pitch
diameter. Sometimes referred to as the simple
effective diameter to differentiate from the virtual
effective diameter.
Effective Nut Diameter:
Twice the effective nut radius.
Effective Nut Radius:
The radius from the centre of the nut to the point
where the contact forces, generated when the nut is
turned, can be considered to act.
Elastic Deformation:
A change in dimensions directly proportional to and
in phase with an increase or decrease in applied
force.
Elasticity:
The property of a material by virtue of which
deformation caused by stress disappears upon removal
of the stress. A perfectly elastic body completely
recovers its original shape and dimensions after
release of stress.
Elastic Limit:
The maximum stress that a material is capable of
sustaining without any permanent strain
(deformation) remaining upon complete release of the
stress.
Electrical Conductivity:
Metals carry electric currents with varying
capacities. As a relative guide to the conductivity
of different metals, with electrolytic copper rated
at 101 under the International Annealed Copper
Standard at 68 degrees F., 18-8 stainless rates is
rated at 5; silicon bronze 651 at 12; and brass at
27.
Electroless Nickel:
A relatively thin, hard coating that can be applied
to threads and deposited uniformly. Bright metallic
in appearance this coating has excellent resistance
to wear and corrosion.
Electroless Plating:
Electroless nickel (EN) plating is a chemical
reduction process which depends upon the catalytic
reduction process of nickel ions in an aqueous
solution (containing a chemical reducing agent) and
the subsequent deposition of nickel metal without
the use of electrical energy.
Electrolyte:
( 1) A chemical substance or mixture, usually
liquid, containing ions that migrate in an electric
field. (2) A chemical compound or mixture of
compounds which when molten or in solution will
conduct an electric current.
Electroplating: Electroplating is the deposition of a metallic
coating onto an object by putting a negative charge
onto the object and immersing it into a solution
which contains a salt of the metal to be deposited.
The metallic ions of the salt carry a positive
charge and are attracted to the part. When they
reach it, the negatively charged part provides the
electrons to reduce the positively charged ions to
metallic form.
Electropolishing Stainless:
Electropolishing process removes oxides and
impurities from the surface of the metal and leaves
a sterile and passive finish. Electropolishing
smoothes, polishes, deburrs, and cleans stainless
steel parts resulting in a smooth, high luster
finish. Because the metal part is bathed in oxygen,
there is no hydrogen embrittlement. Electropolishing
removes hydrogen from the surface of the part and
because bacteria cannot successfully multiply on a
surface without hydrogen, electropolishing is idea
for medical, pharmaceutical, semi-conductor, and
food processing equipment and parts.
Elevator Bolt:
A flat, plain, circular countersunk head bolt with a
square neck to prevent rotation.
Elongation:
Stretching a fastener to the point that it breaks.
The percent of elongation at rupture (same as
measure of ductility) is determined by dividing the
total length after stretching to the original
length. Elongation decreases as strength and
hardness increases.
Embrittlement:
Loss of load carrying capacity of a metal or alloy;
The severe loss of ductility or toughness or both,
of a material, usually a metal or alloy. Many forms
of embrittlement can lead to brittle fracture. Many
forms can occur during thermal treatment or
elevated-temperature service (thermally induced
embrittlement). Some of these forms of embrittlement,
which affect steels, include blue brittleness, 885
ºF (475 ºC) embrittlement, quench-age embrittlement,
sigma-phase embrittlement, strain-age embrittlement,
temper embrittlement, tempered martensite
embrittlement, and thermal embrittlement. In
addition, steels and other metals and alloys can be
embrittled by environmental conditions
(environmentally assisted embrittlement). The forms
of environmental embrittlement include acid
embrittlement, caustic embrittlement, corrosion
embrittlement, creep-rupture embrittlement, hydrogen
embrittlement, liquid metal embrittlement, neutron
embrittlement, solder embrittlement, solid metal
embrittlement, and stress-corrosion cracking.
885-ºF (475-ºC) Embrittlement:
Embrittlement of stainless steels upon extended
exposure to temperatures between 400 and 510 ºC (730
and 930 ºF). This type of embrittlement is caused by
fine, chromium-rich precipitates that segregate at
grain boundaries: time at temperature directly
influences the amount of segregation. Grain-boundary
segregation of the chromium-rich precipitates
increases strength and hardness, decreases ductility
and toughness, and changes corrosion resistance.
This type of embrittlement can be reversed by
heating above the precipitation range.
Endurance Limit:
The maximum stress that a metal will withstand
without failure during a specified large number of
cycles of stress.
Environmental Cracking:
Brittle fracture of a normally ductile material in
which the corrosive effect of the environment is a
causative factor. Environmental cracking is a
general term that includes corrosion fatigue,
high-temperature hydrogen attack, hydrogen
blistering, hydrogen embrittlement, liquid metal
embrittlement, solid metal embrittlement,
stress-corrosion cracking, and sulfide stress
cracking. The following terms have been used in the
past in connection with environmental cracking, but
are becoming obsolete: caustic embrittlement,
delayed fracture, season cracking, static fatigue,
stepwise cracking, sulfide corrosion cracking, and
sulfide stress-corrosion cracking.
Environmentally Assisted Cracking:
(EAC) A process that can occur with the use of high
strength steel fasteners in which crack initiation
and growth occurs in the fastener at a comparatively
low stress level as a result of interactions that
occur with the environment. Hydrogen is suspected of
causing EAC in high strength steel fasteners, the
hydrogen being produced as a result of chemical
reactions (galvanic corrosion in a moist
environment) or being present from a plating process
that may have been applied to the fastener.
Erosion Corrosion:
Erosion corrosion is an acceleration in the rate of
corrosion attack in metal due to the relative motion
of a corrosive fluid and a metal surface.
Escutcheon Pin: A piece generally used to join a plate or shield, to
cover or protect softer or more delicate materials
or actions.
Expansion Bolt:
A combination of a "lag bolt" and an internally
threaded split sleeve, designed for fastening to
stone or concrete by inserting a sleeve into a hole
in the concrete and expanding to a tight fit in the
hole by turning the lag both with a wrench.
External Force or Load:
Forces exerted on a fastener as a result of an
applied loading to the joint.
External Thread:
A screw thread which is formed on an external
cylinder, such as on bolts, screws, studs etc. Slang
- the male thread.
Extruding:
When cold forming produces a fastener before
threading with two different diameters. The portion
with the larger diameter is the shoulder; the
smaller portion will be roll threaded. In the
extruding process, a manufacturer starts with raw
material equal to the shoulder diameter and pushes
part of it through a die, reducing the diameter of
the portion which will later be roll threaded.
Eyebolt:
A bolt having a head in the form of an open or
closed anchor ring, or of a flattened and pierced
section, with or without a collar or shoulder under
the head.
F593, F594, FF593C:
F593 is a specification for stainless hex head cap
screws; F594 is for stainless nuts. Compared to
regular stainless fasteners, F593 and F594 call for:
(a) tensile requirements about 20% higher than that
of commercial 18-8 or stainless hex caps and nuts to
MS specifications (MS35307-8, MS34649-50); (b) both
a minimum and a maximum tensile and hardness
requirements while commercial and MS fasteners do
not have a maximum; (c) chemical requirements that
are somewhat bizarre, eliminating many commonly used
mixtures of 300 or 18-8 stainless while allowing
others.
Face:
To machine a flat surface perpendicular to the axis
at rotation on a lathe.
Failure:
A general term used to imply that a part in service
(1) has become completely inoperable, (2) is still
operable but is incapable of satisfactorily
performing its intended function, or (3) has
deteriorated seriously, to the point that it has
become unreliable or unsafe for continued use.
Fatigue:
Metal failure due to stresses that push first in one
direction and then another.
Fatigue Life:
The number of cycles of stress that can be sustained
prior to failure under a stated test condition.
Fatigue Corrosion:
Caused by repeated stress in a corrosive atmosphere
and is generally not associated with stainless.
Fatigue Limit:
The maximum stress that presumably leads to fatigue
fracture in a specified number of stress cycles. If
the stress is not completely reversed. the value of
the mean stress. the minimum stress, or the stress
ratio should also be stated. Compare with endurance
limit.
Fatigue Strength:
The stress to which a metal can be subjected for a
specified number of cyclic changes of stress.
Feather Key:
A parallel key fastened in either the shaft or in
the hub of a member sliding on it. When fastened in
the shaft, it must be long enough to hold or drive
the sliding member in any of its positions on the
shaft. When in the sliding member the key need only
be as long as the hub.
Ferritic Stainless:
Comprising less than 5% of stainless fasteners,
mainly type 430, it is magnetic and not hardenable
by heat treatment. Though containing no nickel,
ferritic stainless has a high chromium content
providing greater corrosion resistance than
martensitic stainless but much less then austenitic.
It is mainly used by the automotive and building
industries for decorative trim, architectural
hardware, handrails, moldings on various products.
Fillet:
A rounded filling of the internal angle between two
surfaces.
Fillister Head:
Rounded top surface, cylindrical sides, and a flat
bearing surface.
Fin:
A thin projecting rib.
Finished
Fastener: A finished fastener is a fastener made
to close tolerances and having surfaces other than
the threads and bearing surface finished to provide
a general high grade appearance.
Finished Hexagon Bolts:
A washer faced or chamfered bearing surface with a
close body tolerance.
Fin Neck Carriage Bolt:
A plain, circular, oval head bolt with two
oppositely located fins to prevent rotation. IFI now
refers to this fastener as a Round Head Fin Neck
Bolts.
Fit:
The general term used to signify the range of
tightness which may result from the application of a
specific combination of allowances and tolerances in
the design of mating parts. See "Class of Thread"
Flat Head:
Flat top surface and a conical bearing surface.
Flex-Loc:
When used as a stop or lock nut, the locking threads
of the slotted top press inward against the bolt,
lifting the nut upward and causing the remaining
threads to bear against the lower surface of the
bolt threads.
Fluoro-Carbon Thread Coating:
A low friction coating applied to threads. This type
of coating is frequently used to prevent thread
fouling when a assembly containing threaded
fasteners is painted. Unless masked in some way
before painting, electro deposited primers can cover
the threads. If this occurs assembly difficulties
can result unless the expensive chore of cleaning
the threads is completed. A fluoro-carbon thread
coating eliminates the need for masking or cleaning
since paint will not adhere to the coating. This
type of coating can also prevent problems caused by
weld splatter obstructing the threads of weld nuts
during their placement. Such coatings also have the
property of reducing the torque-tension scatter
during tightening.
Forge:
To shape metal while holt and plastic by a hammering
or forcing process. Dies used in process.
Form of Thread:
The profile of a thread in an axial plane for a
length of one pitch.
Fouling:
An accumulation of deposits. This term includes
accumulation and growth of marine organisms on a
submerged metal surface and also includes the
accumulation of deposits (usually inorganic) on heat
exchanger tubing.
Fractography:
Descriptive treatment of fracture, especially in
metals, with specific reference to photographs of
the fracture surface. Macrofractography involves
photographs at low magnification (< 25x);
microfractography, photographs at high magnification
(>25x)
Fracture Mechanics:
A quantitative analysis for evaluating structural
behavior in terms of applied stress, crack length,
and specimen or machine component geometry. See also
linear elastic fracture mechanics.
Fracture Toughness: A generic term for measures of resistance to
extension of a crack. The term is sometimes
restricted to results of fracture mechanics tests,
which are directly applicable in fracture control.
However, the term commonly includes results from
simple tests of notched or precracked specimens not
based on fracture mechanics analysis. Results from
test of the latter type are often useful for
fracture control, based on either service experience
or empirical correlations with fracture mechanics
tests. See also stress-intensity factor.
Free Carbon:
The part of the total carbon in steel or cast iron
that is present in elemental form as graphite or
temper carbon. Contrast with combined carbon.
Free Corrosion Potential:
Corrosion potential in the absence of net electrical
current flowing to or from the metal surface.
Free Machining: The property that makes machining easy because of
the forming of small chips, a characteristic
imparted to steel by sulfur, etc.
Fretting Corrosion: Occurs when vibration causes a stainless fastener to
continually rub against another surface, resulting
in the passive oxide film on stainless rubbing off.
Fretting corrosion might occur in high tensile
fasteners such as martensitic stainless.
Friction:
Mechanical resistance to the relative movement of
two surfaces. There are two main types of friction;
Static Friction and Dynamic Friction. Typically
static friction is greater than dynamic friction.
Friction Stabilizers:
Coating materials used on fasteners with the
intention of reducing the scatter in the thread and
bearing surface friction coefficients.
Full Annealing:
Annealing a ferrous alloy by austenitizing and then
cooling slowly through the transformation range.
Full-Size Body:
The body of a bolt or screw which has a diameter
between the minimum and maximum limits of the major
diameter of the thread.
Fundamental Deviation:
An intentional clearance between internal or
external thread and the design form of the thread
when the thread form is on it's maximum metal
condition. For metric threads the fundamental
deviation are designated by letters, capitals for
internal threads and small letters for external
threads. Some tolerance classes have a fundamental
deviation of zero. For imperial threads the
fundamental deviation is called the allowance.
Fundamental Triangle Height:
The fundamental triangle height is normally
designated with the letter H. This is the height of
the thread when the profile is extended to a sharp
vee form. For 60 degree thread forms such as metric
and Unified thread series, H equals 0.866025 times
the thread pitch.
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