Bolt, Nut and Washers Terminology

 
Head
The Head: The top part of a bolt (not the threaded end) is called the head. There are many different types of bolt heads, which can be turned using a spanner or driver.

 
Shank
A shoulder is a term that can be used to describe this unthreaded portion of a bolt. Bolt Shoulders exist for two reasons. The first is to create an area on the bolt where sheering is less likely to occur. If a load is pulling sideways against the unthreaded area of a bolt then the bolt will be less likely to snap as the area where the pressure is being placed is stronger than the threaded portion. The second reason for a shank is to allow for more versatile uses. This shank can act as an area for something attached to the bolt to be moved around.
 
Driving threaded fasteners
The "drive" of a fastener is the area of the screw or bolt where a tool is used to turn it, such as a screwdriver, bit, socket, or wrench. The drive is a set of shaped cavities and protrusions on the fastener head that allows torque to be applied to it
 

Nut
A nut is a type of fastener with a threaded hole that is used to fasten multiple parts together with a mating bolt. The nut is the female member of the pair, with internal threads that match those of the bolt. The bolt is the cylindrical metal shaft with a threaded end. The two parts are kept together by a combination of their threads' friction, with slight elastic deformation, and a slight stretching of the bolt.
 

 
Washers
Washers are thin plates with a hole in the centre that are used to distribute the load of a threaded fastener, such as a bolt or nut. They can be made of metal or plastic, and there are many different types, including flat, lock, split, star, Belleville, and wave. Washers can also be square.