A type of fastener with a threaded hole.

Used in assembly with a mating bolt to torque multiple parts together.

These parts are combined by the threads' friction.

The shaft of the bolt prevents radial movement of the parts. 

Simultaneously, the head of the bolt & the nut prevent axial movement.

Hex nut is the most common type of nut.

The hexagonal outer shape generate torque when fastening..

Stretching of the bolt & the compression from the rest part keep the combination.