Types of nuts

A nut is a fastener that consists of a block with a threaded hole in the centre. The hole contains ‘female’ threads that typically correspond to the ‘male’ threads of a bolt or screw. Nuts are used with their ‘mating’ bolt or screw to fasten materials together.

The most common shape for a nut is hexagonal, as six sides provide more angles for a tool to approach from, although the corners can be more vulnerable to becoming rounded off over time which makes them less easy to use with tools. Square nuts can also be used but are less common.

Vibration or rotation can have the effect of loosening a nut over time and so different locking mechanisms can be used, including:

Locking washers.
Jam nuts or locking nuts.
Thread-locking fluid.
Oval-shaped threads.

Nuts are used for many different applications and so there are a wide variety of different types. Some of these include:

Basic hex nut: A six-sided nut, and the most common type. There are several variations such as the nylon insert lock which helps secure the nut in place.
Wing nut: The head of a wing nut has two ‘wings’ on each side, enabling it to be tightened and loosened by hand. Mainly used for temporary fastening.
Cap nut: This type of nut is closed at one end with a smooth-domed top.
Acorn nut: Similar to a cap nut but the rounded end has a higher crown.
Barrel nut: Also known as a dowel nut, this has a round ‘slug’ with threads perpendicular to its length.
Cage nut: A spring steel cage wraps around the nut with wings that can be used to compress and release the nut.
Coupling nut: A threaded fastener for joining two male threads together, such as in pipework, or to make long rod assemblies from shorter lengths.
Flange nut: A wide flange at one end acts as an integrated washer, distributing the pressure of the nut over the part being secured.
Insert nut: Inserted into a pre-drilled hole to provide a threaded socket.
Split nut: Split into two pieces to allow the female thread to open and close over the male thread of a bolt or screw.
Square nut: A four-sided nut which provides greater resistance to loosening.
Swage nut: Also known as a self-clinching nut, this is used to permanently anchor itself onto sheet metal.
T-nut: A long, thin body with a T-shaped flange at one end which digs in, leaving a flush surface.
Weld nut: A specialised nut that can be welded to another component.