Nut (fastener)

A nut is an accessory fastening component used with some screws and bolts. In general, it has an inner hole that is threaded to receive the male threads of the fastener, and an outer hard shell, usually hexagonal or square, that can be turned with a tool called a wrench. The wrench can be turned either in a direction to tighten or loosen the bond between nut and screw/bolt.

The most common hand wrenches either are open-ended, such that they have sides parallel to two or more facets of the nut, or variously called box or socket, which surround all sides of the nut. A box wrench is a hand tool that can drop over the nut no matter how much of the screw or bolt protrudes, while a socket wrench has a maximum depth of shaft that it can accept. The advantage of sockets is that they can be attached to a wide range of drivers, for mechanical power advantage and sometimes simply to reach the nut through a flexible driveshaft.