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Last edited 26 Apr 2018
Types of bolts
A bolt is a type of fastener, usually made from metal, that commonly comprises a head at one end, a chamfer at the other, and a shaft characterised by an external helical ridge known as a ‘thread’. Bolts are typically used to hold materials or objects together, or to position objects.
The chamfer at the opposite end of the head provides a slightly bevelled edge which helps with inserting the bolt into holes and nuts. Bolts typically (but not always) require a nut which is applied via torque while the bolt is held in place (or vice versa). Vibration or dynamic loads may loosen nuts, necessitating the use of locknuts, lock washers or thread lockers which can provide resistance to loosening.
The terms ‘bolts’ and ‘screws’ are sometimes used interchangeably, and the distinction between them can be complex, however, in simple terms, a bolt passes through the materials it is fixing together (typically into a nut at the other side), whereas a screw threads directly into them.
 Types of bolt
Has a T-shaped head which can be gripped by a wench and can fit into a slot with ease.
Different types of head include:
- Square shoulder: A truss head, shaped so as to allow fastening with the least amount of surface obstruction, on a square shank which resists rotation.
- Indented hexagon: For use with a wrench, this head has a circular depression in its top surface.
- Indented hexagon washer: Same as an indented hexagon, but with the addition of a washer section at the base to protect the assembly finish from the wrench.
- Hexagon (trimmed): Standard type of head, with clean corners that are trimmed to close tolerances.
- Hexagon flange: Similar to the indented hexagon washer, but the washer is conical or slightly rounded.
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