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!

# A B C D E F G H I J K L M N O P Q R S T U V W Y Z

#3 or #7: Refers to head design of a plow bolt

&NT: With nut

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

AS: Alloy Steel

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

BHCS: Button Head Cap Screw

BHN: Hardness measured with a Brinell Hardness Tester

BHR: Button Head Robertson

BHS: Button Head Hex Socket

BHT: Button Head Torx Socket

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.

BR: Brass

BRS: Brass Material

BRZ: Bronze Material

BS: British Standard

BSF: British Standard Fine

BSW: British Standard Whitworth

BT: Bolt (on drawings)

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

CAR: Carriage Bolt/Screw

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.

COO: Country of Origin

Countersunk Head: A fastener with underside of head beveled to fit a flaring hole. Most head types have bearing surface perpendicular to body axis.

CPR: Copper Material

CR: Chrome

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

CSL: Castellated Nut

CSS: Countersunk screw (flat or oval head)

CT: Coarse thread

D/C Nut: Double Chamfered Nut (distinguish from washer faced)

D/E: Double Ended Stud

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.

DWS: Drywall Screw

ESL: External Star Lockwasher

ESN: Elastic Stop Nut, normally a hex nut with a nylon locking insert

ET: External Thread

External Thread: The male thread is external from the cylinder surface.

F: Fully threaded

F436: Hardened flat washer with dimensions per ASTM F436

FAB: Fabric Material

FB: Flange Bolt

FDR: Fender Washer

FH: Flat Head

FHCS: Flat Head Cap Screw

FHH: Flat Head Hex Socket Screw

FHP: Flat Head Phillips Screw

FHR: Flat Head Robertson Screw

FHS: Flat Head Slotted Screw

FHT: Flat Head Torx Socket Screw

FIL: Fillister Head

FIM: Full Indicator Measurement

FIN: Finishing (washer)

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

FLG: Serrated Flange Nut

Flng: Hex Flange Bolt or Nut

FLT: Flat Washer

FNDR: Fender (washer)

FT: Fine thread or fully threaded

FW: Flat Washer

G: Grade

Galv: Galvanize (typically refers to Hot Dip Galvanized)

Galvi: Galvanize

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)

GV: Galvanized

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

HD: Head

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)

HHMB: Hex head machine bolt

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

HT (H.T.): Heat treated

HVHX: Heavy pattern hex bolt

HWH: Hex Washer Slotted Head Screw

HX: Hex

HYD: Hydraulic

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

IH: Indented Head

In.: Inch

INS: Insulated

Internal Thread: Female thread is on the inside surface of a cylinder or cone, as in a threaded hole or nut.

IRS: Inner Rollstop

ISIR: Initial Sample Inspection Report

ISL: Internal Star Lockwasher

ISO: International Standards Organization

IT: Internal Thread

J429: SAE Standard that specifies strength levels of screws

J995: SAE Standard that specifies strength levels of nuts

JAM: Thin Hex Nut or Jam Nut

JMNT: Jam nut

Keps: Nut with a permanently attached washer

Kips: 1,000 pounds

KSI: Thousand pounds per square inch

LB: Lag bolt, or body length on screws

Lbs: Weight in pounds

LCS: Low carbon steel

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

LH: Left-hand thread

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.

LTX: Latex Material

LW: Lockwasher

M: Metric

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.

MB: Machine Bolt

Mfg.: Manufacturer

Minor Diameter: The smallest diameter of a straight thread, measured at the root of an external thread or the crest of an internal thread.

MS: Machine Screw

MSNT: Machine Screw Nut

MTR: Motor, or Material Test Report

NC: National Coarse Thread

NE: Designation that defines thickness of a nylon insert lock nut

NF: National Fine Thread

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.

NPN: Neoprene Material

NPT: National Tapered Pipe Thread

NT: Nut

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

NYL: Nylon Material

OH: Oval Head

OHP: Oval Head (countersunk) Phillips Screw

OHS: Oval Head (countersunk) Slotted Screw

OV: Oval Head

p: Thread Pitch

P: Philips

P/N: Part number

Passivate: Surface treatment to neutralize stainless steels as an aid in resisting corrosion. An oxidizing solution is used.

PB: Plow Bolt

PBK: Piggyback Slip Crimp Terminal

PEN: Polyethylene Material

PH: Philips Head

Ph Dr: Phillips Drive (cross recess)

Phil.: Philips Drive

Phos (P & O): Phosphate and Oil Coating (typically Zinc Phosphate and Oil)

PHP: Pan Head Phillips Screw

PHR: Pan Head Robertson Screw

PHS: Pan Head Slotted Screw

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.

PL: Plain finish

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.

PMP: Pump

PN: Pan Head

POP: Blind Hole “pop” Rivet

Pozi Drive: Special cross recess (registered trademark of Camcar Textron)

PPAP: Production Part Approval Process

PPN: Polypropylene Material

PSI: Pounds per square inch

PSR: Pan Head Slotted Robertson Screw

PT: Partial Thread

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

RBR: Rubber Material

RC: Hardness measured on the Rockwell C Scale

RD: Round Head

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

RHS: Round Head Slotted Screw

Right-Hand Thread: A clockwise winding thread of a fastener (when viewed from the starting end).

RNG: Ring Crimp Terminal

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.

RT: Rolled Threads

S: Slotted

S/S: Stainless Steel

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.

SBR: Silicon Bronze

SCL: Self-Clinching “Pem” Nut or Screw

Screw: An externally threaded fastener with any type of head.

SD: Square Drive

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

SHCS: Socket Head Cap Screw

SKT: Socket

SL: Slotted

Slot.: Slotted Drive

SLP: Slip-on Crimp Terminal

SMI: Semi-Tubular Rivet

SMS: Sheet Metal Screw

SPL: Split Lockwasher

SQ: Square

SQR: Square Nut or Screw Head

SS: Stainless Steel or Set Screw

SSC: Shoulder Screw Custom, requires drawing

SSS: Shoulder Screw Standard Hex Socket

SST: Stainless Steel, 304 unless specified

ST: Steel

STD: Standard

STL: Steel

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)

TEE: “T” Nut or Connector

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.

THS: Truss Head Slotted Screw

TIR: Total Indicator Reading

Torquing: Tightening a threaded fastener to an indicated torque value.

Torx: 6 Lobe Drive (Torx Drive, registered trademark of Camcar Textron)

TPI: Threads per inch

TS: Tapping Screw

TT (TR): Taptite Thread (registered trademark of Reminc), also called Tri-Roundular

TTH: Threaded to Head

TWS: Threshold Warning Device

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

VNL: Vinyl Material

W/F: Washer Faced (can refer to a nut or cap screw)

WAC: Width Across Corners

WAF: Width Across Flats

WDC: Worm Drive Hose Clamp

Whitworth: British Thread Standard (not the same as UN threads)

WNG: Wing Nut or Screw

WS: Wood Screw

Y: Yellow Chromate

YS: Yield Strength

Zn (Z): Zinc

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

Zn/Y: Zinc plating with yellow chromate topcoat