Fastener Terminology Guide

By Pankaj International – Global Manufacturer & Exporter of Industrial Fasteners

Understanding fastener terminology is essential for engineers, buyers, and technicians who work with bolted joints, mechanical assemblies, and structural applications. This glossary covers fundamental and advanced fastener terms used across industries such as automotive, construction, oil & gas, heavy engineering, railways, and general manufacturing.

A

Anchor – A fastener designed to provide holding power in materials that cannot support screws directly, such as concrete, brick, or drywall.

Alloy Steel – High-strength steel containing elements like chromium, molybdenum, and nickel to enhance durability and performance.

Anodizing – An electrochemical process used on aluminum fasteners to increase corrosion resistance and surface hardness.

Anti-Seize – A thread lubricant that prevents galling and seizing and makes disassembly easier.

Assembly – A set of fastener components supplied together — for example, a bolt with a washer.

ASTM Standards – Material and performance specifications defined by ASTM International (e.g., A193, A194, A307).

B

Bearing Surface – The area of a fastener that comes into contact with the material being clamped.

Bi-Metal Fastener – A fastener made from two different metals to achieve specific strength or corrosion resistance requirements.

Black Oxide – A conversion coating that provides mild corrosion resistance and a uniform black appearance.

Blind Rivet – A rivet that can be installed from one side of the workpiece.

Bolt – A threaded fastener typically used with a nut and tightened using torque.

C

Carriage Bolt – A bolt with a rounded head and square neck to prevent rotation during tightening.

Clamping Force – The compressive force created when a fastener is properly tightened.

Coarse Thread – Threads with a larger pitch for quicker assembly and greater resistance to stripping.

Cold Forging – A manufacturing process where fasteners are formed at room temperature for improved strength.

Corrosion Resistance – The ability of a fastener to resist rust and chemical degradation.

Counter sunk – A conical recess created for flush installation of countersunk fasteners.

D

Diameter (Major / Minor) – Major diameter: maximum thread diameter. Minor diameter: minimum root diameter of the thread.

DIN Standards – German standards for fasteners (e.g., DIN 933, DIN 934).

Drive Type – The pattern used to engage a fastener, such as Phillips, Slotted, Hex, TORX®, etc.

Double-End Stud – A stud threaded on both ends with an unthreaded shank between, commonly used in flanges.

Ductility – A measure of how much a fastener can deform without breaking.

E

Electro-Galvanizing – A zinc coating process that provides good corrosion protection with a bright finish.

Elongation – The amount a fastener stretches before failure — an indicator of ductility.

F

Fastener – A mechanical device used to join two or more components together.

Fatigue Strength – A fastener’s ability to withstand repeated loading cycles without failure.

Flange – A rim or collar on a bolt or nut used to distribute load.

Friction Coefficient (K-Factor) – A key factor in torque-tension calculations affecting preload accuracy.

G

Galling – Thread damage caused by friction and adhesion, especially common in stainless steel.

Grade – Strength classification for fasteners (e.g., 8.8, 10.9, Grade 5, Grade 8, A2-70).

Grip Length – The total thickness of material being clamped beneath the fastener head.

H

Hardness – The ability of a fastener to resist wear and indentation.

Hex Head – A six-sided head commonly used on bolts and screws for wrench tightening.

Hot-Dip Galvanizing (HDG) – A thick zinc coating applied by dipping fasteners in molten zinc for superior outdoor corrosion protection.

Hydrogen Embrittlement – A brittle failure mode caused by hydrogen absorption during plating or improper processing.

I

Impact Resistance – The ability of a fastener to withstand sudden forces without cracking.

ISO Standards – International specifications for fasteners (e.g., ISO 4014, ISO 4032).

M

Machine Screw – A fully threaded screw designed for use with a tapped hole or nut.

Mechanical Galvanizing – A zinc coating method that eliminates hydrogen embrittlement risk for high-strength fasteners.

Metric Thread – Thread dimensions defined in millimetres (e.g., M8 × 1.25).

Micro-Encapsulated Adhesive – Adhesive applied to threads that activates during installation for locking and sealing.

N

Nominal Diameter – Basic size designation of a fastener (e.g., M10, 1/2").

Nut – An internally threaded component used with a bolt to form a secure joint.

Nyloc Nut – A nut with a nylon insert that provides vibration resistance.

P

Passivation – Chemical treatment of stainless steel to remove free iron and enhance corrosion resistance.

Pitch – The distance between thread crests; determines thread fineness or coarseness.

Plating / Coating – Protective layers applied to fasteners such as zinc, HDG, black oxide, or zinc-nickel to prevent corrosion.

Proof Load – The maximum load a fastener can withstand without permanent deformation.

R

Relaxation – Loss of preload over time due to material settling, embedment, or thermal cycles.

Residual Stress – Internal stresses that remain within a fastener after manufacturing or tightening.

Rivet – A permanent mechanical fastener installed by deforming one end to form a head.

Rivet Nut – A threaded insert that allows bolts to be used in thin or difficult-to-tap materials.

S

Salt Spray Test (SST) – An accelerated corrosion test used to evaluate coating performance.

Self-Tapping Screw – A screw that forms or cuts its own mating threads during installation.

Shear Strength – The resistance of a fastener to forces applied parallel to its axis.

Socket Head – A cylindrical head tightened with an Allen (hex) key.

Stainless Steel – A corrosion-resistant alloy commonly used for durable fasteners (A2, A4 grades).

T

Tensile Strength – The maximum axial load a fastener can withstand before breaking.

Thread Rolling – A cold-forming process that creates threads and increases fatigue strength.

Threaded Rod – A rod with continuous threads used for tensioning, support, and structural applications.

Torque-Tension Relationship – The relationship between applied torque and resulting preload in a fastener.

W

Washer – A thin disk placed under a fastener head or nut to distribute load and prevent surface damage.

Wedge Anchor – A heavy-duty mechanical anchor used in concrete for high-load applications.

Weld Stud – A fastener welded to a base material rather than inserted through a hole.

Work Hardening – Strengthening of metal caused by plastic deformation during forming or use.

Z

Zinc Flake Coating – A high-performance, thin coating (e.g., Geomet®, Dacromet®) that provides corrosion protection without hydrogen embrittlement risk.

Zinc Plating – A common protective coating that offers corrosion resistance and a clean appearance.