A bolt is a type of fastener, that is normally used together with a nut for assembling two unthreaded components.

The ease to use made them suited to play an important role in the development of mass-produced articles and steel structures.

It consists of a head and a cylindrical body that is externally parallel threaded along a portion of its length.

The head is the part of the bolt with the largest diameter and its shape is designed to fit the correspondent tightening tools. Bolts’ head can also perform other functions such as spreading the clamping load over the bearing surface or locking the bolt in place, stopping rotation.

The thread is a helical structure wrapped around the cylinder of bolts which is used to convert between rotational and linear movement, while ensuring the tightening of fasteners.

There are many forms of threads but two types are the most common. Spaced threads are used on woodscrews and self-tapping screws while machine screw threads are generally used on bolts and are designed to couple with preformed threads in nuts or tapped holes. Machine screw threads vary in accordance with helix shape and sizes, as specified in different international standards. For example the ISO thread (metric), Whitworth thread (in inches) or GAS thread (in inches).

Some kind of bolts have a thread that runs from underneath the head to the tip. However, bolts can be also partially threaded. That means they have an area, below the head, that is entirely free of threads. The length of this non-thread area, also referred to as bolt shank or shoulder, can vary depending on the type of bolt.

Both configurations offer a specific advantage in accordance with the use a bolt is intended to.

Fully threaded bolts spread the tightening tension along its entire length, with the largest holding pressure placed on the head, where it meets the material it fastens to. This kind of bots are the right choice when grip strength is very critical. Moreover, they rarely shear and tend to not loosen as well.

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