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Threaded Fasteners - Glossary of Terms

A

A2 - The most commonly produced grade of stainless steel. Also known as grade or type 304.
A4 - The second most commonly produced grade of stainless steel. Also known as grade or type 316.
A/F - A shortened form of 'width across flats'.
Acorn Nut - Another name for a dome nut.
Allen Key - A tool with a hexagonal cross section used for tightening up screws with a socket head.
Allthread - A metal bar that has a thread all along its length.

B

BSC - An acronym for British Standard Cycle, an imperial based thread standard with extra fine pitch for use on bicycles and motorcycles.
BSW - An acronym for British Standard Whitworth, an imperial based thread standard introduced in 1841 but now largely superceded.
BSF - An acronym for British Standard Fine, an imperial based thread standard used where a finer pitch is desired over BSW.
Bolt - A threaded fastener for use with a nut and washer or tapped hole. 'Bolt' is a term that can be used almost interchangably with 'screw', as they are both general terms. A more specific use of this term might be a hex headed fastener with a shank.

C

Cap Nut - Another name for a dome nut.
Carriage Bolt - A large bolt used for joining wooden parts to metal. On tightening the bolts square neck bites into the wood locking it into position allowing the opposite end to be secured with a nut.
Chipboard Screw - A type of wood screw that is widely used.
Circlip - A fastener type used for holding parts in position on a shaft. Designed to sit in a groove on a shaft or in a tube.
Coach Screw - A large screw for use with wooden assemblies.
Coarse Pitch - In contrast to a fine pitch, a thread type with a wider pitch.
Cotter Pin - A pin with a split all the way down it allowing it to be bent apart to lock something in place.
Counterbore - The process of allowing the head of a bolt to sit recessed into the surface of the item it's being screwed into.
Countersink - The process of adding a chamfer to the edge of a hole to allow a countersunk headed screw to sit flush or recessed on the surface of the item it's being screwed into.
Cut Thread - A thread that has been cut on a blank typically by a lathe, rather than rolled.

D

DIN Number - A number that represents the standard to which a particular fastener has been manufactured to and complies with. For example DIN 931 refers to hex head bolts.
Dome Nut - A nut with a closed end in the shape of a dome to give a tidy finish.

E

F

Fine Pitch - As opposed to coarse pitch, a thread where the pitch is narrower.

G

Galling - An undesirable characteristic of stainless steel threaded fasteners where they appear to seize on installation.
Grub Screw - A headless threaded fastener typically used in door handles for example.

H

Hoseclamp - Generally, a more heavy duty type of hoseclip used for more high pressure applications.
Hoseclip - A fastener that is used to hold hoses in place on an assembly. Normally incorporates a worm drive to accomplish this.

I

J

Jam Nut - Another term for a lock nut.

K

L

Lock Nut - A hex nut that has a thinner profile to a standard hex nut. Normally used in pairs to help prevent loosening in use.

M

Metric - In terms of fasteners, a thread standard that is based on the metric system rather than imperial measurements.

N

Nyloc Nut - A nut type incorporating a nylon ring to help prevent it loosening in use.

O

P

P-Clip - A 'P' shaped clip used for securing pipes and cables on an assembly.
Pitch - On metric fasteners the distance between the crest of each individual thread. On imperial fasteners the pitch is measured by counting the threads per inch.

Q

R

Rolled Thread - The preferred method for producing a thread on a shaft. This method creates a thread that is less likely to shear and is less likely to suffer issues such as galling on installation.

S

Self Tapping Screw - A screw designed to cut it's own thread on installation. Normally used in sheet metals and plastics.
Setcrew - A hex headed fastener with a shaft threaded all the way to the head. Can also be another term for a Grub Screw.
Shank - Can refer to the non threaded part of the shaft of a screw or bolt, or the whole shaft underneath the head.
Socket Head - Screw head type featuring a hexagonal recess which allows tightening with the use of an allen key. Examples include socket head cap screws and socket head button screws.
Split Pin - See Cotter Pin.
Stainless Steel - A family of steel alloys noted particularly for their resistance to corrosion.

T

Tap - The process of adding a thread to a hole or nut.
Tapping Screw - See Self Tapping Screw.
Tensile Strength - The maximum amount of longitudinal stress an item can withstand before it will fracture.
Thread - The helical shaped part of a screw that enables it to mesh with a similarly threaded nut to hold something in place on an assembly.

U

UNC - An acronym for Unified National Coarse. An imperial thread standard that is part of UTS, and defines screw threads with a coarse pitch.
UNF - An acronym for Unified National Fine. An imperial thread standard that is part of UTS, and defines screw threads with a fine pitch.
UTS - An acronym for Unified Thread Standard. A standard defining standard thread forms in the United States and Canada. Examples include UNC and UNF.

V

W

Width across flats - The distance between parallel flat edges on a hexagon headed bolt or screw. Indicates the size of spanner required to tighten it.

X

Y

Yield Stress - The amount of stress an item will require subjecting to before it begins to deform plastically i.e. will no longer return to it's original shape.

Z