Fastener Terminology – Fastener Types

 In Education

fastener terminology

The fastener industry, like many others, has its own set of standards, regulations and terminology. Sometimes it can be hard to keep up, so we thought we’d help out by writing a series of posts covering several aspects of fasteners. Hopefully, this will help you find the right fastener for your application or more accurately specify what type of item you are looking for. In this post, we’re going to look at some common fastener types.

Types of Fasteners

thumb screw


A screw is the term used for a threaded fastener, with or without a head (headless – as in set screw) so designed as to permit it to be properly assembled in a pre-formed internal threaded hole (or forming its own thread) and secured by means of tightening the head.



A bolt is a threaded fastener, with a head, designed to be used in conjunction with and properly assembled by means of tightening a nut.

acorn nut


A nut is a geometrically designed block (usually of metal or plastic) with an internal thread and designed to be assembled in conjunction with a bolt or screw.



A washer is a part having a centrally located hole. The washer performs various functions when assembled between the bearing surface of a fastener and the part being attached.

shoulder bolt

Shoulder Bolt / Shoulder Screw

A shoulder bolt (aka shoulder screw) fastener is one in which the shank is held to a precise diameter, known as the shoulder, and the threaded portion is smaller in diameter than the shoulder. Shoulder screw specifications call out the shoulder diameter, shoulder length, and threaded diameter; the threaded length is fixed, based on the threaded diameter, and usually quite short.

Sex Bolts and Binding Posts

Sex Bolts & Mating Fasteners

A sex bolt, (also known as a barrel nut, barrel bolt, ‘Chicago screw‘ or post and screw), is a type of fastener (nut) which has a barrel-shaped flange and protruding boss that is internally threaded. The boss sits within the components being fastened, the flange provides the bearing surface. The sex bolt and accompanying machine screw sit flush on either side of the surfaces being fastened. It is normally chosen because of its low profile compared to other nuts. The sex bolt often has a built-in feature, such as a slot, to aid in tightening the fastener. A sex bolt is a mating fastener combining a fastener (nut) with a fastener (screw). The sex bolt consists of a female (internally) threaded barrel (nut) and a male (externally) threaded screw. Both the barrel and screw have heads designed to clamp (bind) material between the head of the barrel and the head of the screw, or to bridge the gap between two parts.

set screw

Set Screws

A set screw is a threaded fastener that is typically used to hold a sleeve, collar or gear on a shaft to prevent relative motion. It is a threaded member that normally does not have a head. Unlike most other threaded fasteners it is basically a compression device normally used to generate axial thrust. Various socket types are provided to allow the set screw to be rotated. These types include hexagon socket, fluted socket, screwdriver slot and square head. Various point designs are available (the part of the set screw that rotates against the shaft being secured) and include:

  • CUP – Hollowed end, is the most commonly used point style. Used when the digging in of the point is not undesirable.
    Cone – Pointed end, this type generates the highest torsional holding power and is typically used for a permanent connection.
  • OVAL – Rounded end that is typically used when frequent adjustment is required. The oval end prevents/reduces indentation.
  • FLAT – Cause little damage to the shaft and are used when frequent adjustment is required.
  • DOG – Flat end with the threads stopping short of the end with the end fitting into a hole.

We know this is a far from exhaustive list. What other fastener types did we forget, and what are their applications? Tell us in the comments below.

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