This glossary provides definitions and explanations for many terms commonly used in the fastener industry, as well as decoding abbreviations used with fasteners. It’s a great resource for those who may not be as familiar with all the different types of fasteners. Take a look – you just might learn something new!
#3 or #7: Refers to head design of a plow bolt
18-8: Stainless Steel with 18% Chrome and 8% Nickel
2, 5, or 8: Strength grade of screw or nut
2A (3A): Class of thread fit for inch screws
2B (3B): Class of thread fit for inch nuts
2H: Nut strength level designation (ASTM A194 Grade 2H Heavy Hex Nut)
6G: Class of thread fit for metric screws
6H: Class of thread fit for metric nuts
A325: Heavy Hex Structural Bolt (ASTM A325), similar to Grade 5
A490: Heavy Hex Structural Bolt (ASTM A490), similar to Grade 8
A574: Strength grade for socket head cap screws (ASTM A574)
ABS: ABS Plastic Material, a class of plastics based on acrylonitrile-butadiene-styrene copolymers.
Acme Screw Threads: A translating thread form used on fasteners with special thread requirements.
AISI: American Iron and Steel Institute, specifies chemical composition of steels
ALU: Aluminum Material, specify 5052-H32, 6061-T6 or other
AN: Precedes a dimensional specification for aircraft fasteners developed by the Aeronautical Standards Group.
ANSI: American National Standards Institute
ASME: American Society of Mechanical Engineers
ASTM: American Society for Testing and Materials. Used preceding a standard number developed by that group.
B: When followed by a number (ex: B-90), hardness measured on the Rockwell B Scale
Bake (Bake-Out): Heat Treat process used in plating to prevent Hydrogen Embrittlement
Bearing Area: That part of bolt or fastener subjected to bearing load against the wall of the hole.
Bearing Face or Surface: The underside of a bolt head, screw head, or nut.
Belleville: Style of lock washer, also called conical spring washer
Bevel: Style of washer (square with a taper) used with I beams
BHN: Hardness measured with a Brinell Hardness Tester
Body: Area of the screw or bolt that is unthreaded between the thread and the head.
Bolt: A headed fastener, externally threaded. Generally used through a hole with a mating nut as opposed to a screw which is normally used in a threaded hole.
BSW: British Standard Whitworth
BUT: Butt-type wire connector terminal
C: National coarse thread, or when followed by a number (ex: C-35), hardness measured on the Rockwell C Scale
C/R: Cross Recess Drive (typically Phillips style) or Chamfer/Radius
CAD: Cadmium Plating or Computer Aided Design/Drafting
CAD/WAX: Cadmium Plating with a topcoat of Wax
Case Harden: The hardening of a ferrous alloy so the outer area of the case is made harder than the inner section.
Castellated: Having grooves or slots on its upper face.
CH: Case hardened (type of heat treatment)
CL: Class (metric material/strength specification)
Class of Thread: A system used to designate differences in thread tolerance. Classes 1A, 2A, and 3A apply to external threads, and 1B, 2B and 3B to internal threads. Classes 2 and 3 apply to both external and internal threads.
Complete Thread: The part of the thread having full form at both crest and root. Also, to identify threads which extend full distance of specified fastener thread length.
Countersunk Head: A fastener with underside of head beveled to fit a flaring hole. Most head types have bearing surface perpendicular to body axis.
CRES: Corrosion resistant steel (usually refer to 18-8 or 316 stainless steel)
Crest: Term applied to outermost tip of male thread, or the innermost tip of the female thread.
CRS: Cold Rolled/Drawn/Finished Steel, 1008-1020 unless specified
CS: Carbon Steel, or Countersunk
CSS: Countersunk screw (flat or oval head)
D/C Nut: Double Chamfered Nut (distinguish from washer faced)
DAC (DAC 320): Dacromet Coating (registered trademark of Coatings International)
Deltaseal: Magnigard coating (registered trademark of Magni Engineered Coatings)
Dorritech: Magnigard coating (registered trademark of Magni Engineered Coatings)
Driseal: Pipe Thread (registered trademark of Parker Hannifin)
DIN: An abbreviation for Deutsches Institut für Normung, the German standards body. In reference to fasteners, DIN indicates fasteners that conform to a specific metric standard and precedes the standard number.
DLN: Derlin Material, an acetal thermoplastic polymer
Drive Screw: A multi-threaded drive-type fastener which forms mating threads as it is driven into a hole.
Driving Recess: Various types of slots or depressions in fastener head designed to accept a driving tool.
ESN: Elastic Stop Nut, normally a hex nut with a nylon locking insert
External Thread: The male thread is external from the cylinder surface.
F436: Hardened flat washer with dimensions per ASTM F436
FH: Flat Head
FHH: Flat Head Hex Socket Screw
FHR: Flat Head Robertson Screw
FHT: Flat Head Torx Socket Screw
FIM: Full Indicator Measurement
Fin: A thin external rib found on special design fasteners.
Finished Fastener: A close tolerance fastener, with all surfaces finished to give a superior appearance.
FIP: Fillister Head Phillips Screw
FIS: Fillister Head Slotted Screw
FLA: Flag Slip-on Crimp Terminal
FT: Fine thread or fully threaded
Galv: Galvanize (typically refers to Hot Dip Galvanized)
Galvanize: Anti-rust treatment of steel parts, in a bath of lead and zinc.
GR: Grade, refers to strength level of screw or nut (ex: Grade 2, Grade 5 or Grade 8)
Hardened: A product that has been heat treated
Hardening: Heat treating of metals to a desired temperature, not to exceed the critical range, for a given time and then cooling the metal rapidly.
HB: Hex bolt or Hardness reading measured on the Brinell Scale
HCS: Hex Cap Screw or High Carbon Steel
HDG (H.D.G.): Hot Dip Galvanized
Hex: Standard Hex Nut or Screw
Hex Bolt: Can refer to either a “bolt” or a “cap screw”
HHCS: Hex Head Cap Screw (also an abbreviation for Heavy Hex Cap Screw)
Hot Dip Galvanized: The process of dipping fabricated steel into a kettle or vat of molten zinc.
HRB: Hardness measured on the Rockwell B Scale
HRC: Hardness measured on the Rockwell C Scale
HRS: Hot Rolled Steel, 1008-1020 unless specified
HSS: Hex Socket Set Screw, Cup-point
HWH: Hex Washer Slotted Head Screw
Hydrogen Embrittlement: The process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen.
ID: Identification (usually refers to manufacturer logo)
IFI: Industrial Fastener Institute
Internal Thread: Female thread is on the inside surface of a cylinder or cone, as in a threaded hole or nut.
ISIR: Initial Sample Inspection Report
ISO: International Standards Organization
J429: SAE Standard that specifies strength levels of screws
J995: SAE Standard that specifies strength levels of nuts
Keps: Nut with a permanently attached washer
KSI: Thousand pounds per square inch
LB: Lag bolt, or body length on screws
Lead: The distance a threaded fastener moves along its axis in one complete turn.
Left-Hand Thread: When viewed from the starting end of a fastener the thread winds counter-clockwise, whereas a standard right hand thread follows a clockwise direction.
Lentil Head Screw: Term for oval head screw – no longer in common use.
LG: Grip length (distance from head to full threads) on screws
Lockwasher: A washer that is not completely smooth or flat, designed to prevent a nut from loosening, placed under the nut on a screw or bolt.
Magnigard: Magni Coating (registered trademark of Magni Engineered Coatings)
Major Diameter: The greatest diameter of a screw thread. On a machine screw, it is the diameter measured at the crest of an external thread or the root of an internal thread.
Minor Diameter: The smallest diameter of a straight thread, measured at the root of an external thread or the crest of an internal thread.
MTR: Motor, or Material Test Report
NE: Designation that defines thickness of a nylon insert lock nut
Nom: Nominal (reference dimension)
Nominal Diameter: Commonly designated diameter of a fastener as normally ordered, or as specified for assembly purpose.
Non-Ferrous Metal: Any metal or alloy which contains no significant amount of iron, such as copper, brass, aluminum, etc.
Normalize: Process to alleviate internal stress. The part is heated to its critical temperature and allowed to cool slowly.
NPT: National Tapered Pipe Thread
NTE: Designation that defines thickness of a nylon insert lock nut
NTU: Designation that defines thickness of a nylon insert lock nut
NU: Designation that defines thickness of a nylon insert lock nut
OHP: Oval Head (countersunk) Phillips Screw
OHS: Oval Head (countersunk) Slotted Screw
Passivate: Surface treatment to neutralize stainless steels as an aid in resisting corrosion. An oxidizing solution is used.
PBK: Piggyback Slip Crimp Terminal
Ph Dr: Phillips Drive (cross recess)
Phos (P & O): Phosphate and Oil Coating (typically Zinc Phosphate and Oil)
Pitch Diameter: On a machine screw thread, the diameter measured at the point where the width of the groove equals the width of the thread.
Plate: Coating a metal part with a thin layer of another metal by electro-mechanical means.
Plow bolt: A type of fastener that is used for making mechanical connections that require a flush surface at the location where the bolt head protrudes.
Pozi Drive: Special cross recess (registered trademark of Camcar Textron)
PPAP: Production Part Approval Process
PSR: Pan Head Slotted Robertson Screw
PVC: Polyvinyl Chloride Material
PZ: Pozi-Drive style of cross recess
Quenching: The rapid cooling of a metal as used in hardening process.
RB: Hardness measured on the Rockwell B Scale
RC: Hardness measured on the Rockwell C Scale
Ream: Use of a special rotating tool in finishing a hole to critical specifications.
Recessed Head: Any fastener head with a special recess which accepts a matched driving tool.
RH: Round Head, or Right-Hand Thread
RHP: Round Head Phillips Screw
RHR: Round Head Robertson Screw
Right-Hand Thread: A clockwise winding thread of a fastener (when viewed from the starting end).
Roll Threading: Process of rolling a blank piece between two grooved die plates to form threads.
Root: The point at which the minor diameter of a thread is measured.
SAE: SAE Pattern. When used with washers, it means that the washers have a smaller outside diameter than USS pattern washers. When used with screws or nuts, it means US Fine Thread.
SCL: Self-Clinching “Pem” Nut or Screw
Screw: An externally threaded fastener with any type of head.
SEO: Stepless Ear Hose Clamp, Oiled SST
SEMS: Pre-assembled screw and washer combination. Washers are placed on blanks before roll threading. Large diameter of rolled thread allows washer to spin freely without falling off.
Serrated: Locking serrations on bearing face of screw or nut.
Shank: The length of fastener between the head and the point or starting end.
SHC: Socket Hex Head Cap Screw
SS: Stainless Steel or Set Screw
SSC: Shoulder Screw Custom, requires drawing
SSS: Shoulder Screw Standard Hex Socket
SST: Stainless Steel, 304 unless specified
Stud: A rod or cylinder threaded for its entire length.
Tapping Screw: A hardened thread screw which cuts or forms its own mating thread.
Taptite: Special triangular thread forming screw (registered trademark of Reminc)
TH: Through Hardened(type of Heat Treatment)
THP: Truss Head Phillips Screw
Thread Pitch: Distance between threads when measured at the crest or between any corresponding points on adjoining threads.
Thread Series: Standardized diameter and pitch combinations with a designated number of threads per inch for a given diameter. There are eleven such group combinations.
Torquing: Tightening a threaded fastener to an indicated torque value.
Torx: 6 Lobe Drive (Torx Drive, registered trademark of Camcar Textron)
TT (TR): Taptite Thread (registered trademark of Reminc), also called Tri-Roundular
Type 1 (23, 25): Special thread forming or cutting tapping screws
Type AB (F, T): Special thread forming or cutting tapping screws
UNC: Unified National Coarse Thread
UNF: Unified National Fine Thread
UNJ: Unified National Thread with Large Radius Root (special fatigue resistant thread)
UNR: Unified National Thread with Radius Root
UNRC: Unified National Coarse Thread with Radius Root (standard rolled thread form)
UNRC: Unified National Fine Thread with Radius Root (standard rolled thread form)
Upsetting: Axial compression of wire without preheating to form heads on fasteners. Used in the cold-heading process to produce an almost limitless variety of special design products.
USS: USS Pattern. When used with washers, it means that the washers have a larger outside diameter than SAE pattern washers. When used with screws or nuts, it means US Coarse Thread.
UTS: Ultimate Tensile Strength
W/F: Washer Faced (can refer to a nut or cap screw)
Whitworth: British Thread Standard (not the same as UN threads)
Zn/C (ZC): Zinc plating with clear chromate topcoat
Zn Phos: Zinc Phosphate and Oil (same as Phos and Oil)
Zn/Wax: Zinc plating with a topcoat of wax