A socket cap screw, also known as a socket head capscrew, socket screw, or Allen bolt, is a type of cap screw with a cylindrical head and hexagonal drive hole

The most basic difference between a cap screw and a bolt is the way in which these fasteners are installed. Technically, a bolt is installed by turning a nut to tighten the fastener, while a cap screw in installed by turning the head of the bolt to assemble and tighten.

Hex cap screws feature a washer face under the head and a chamfered point. Cap screws are made up of low-carbon steel. These are commonly used in construction or repair projects. A machine screw is generally a smaller Fastener threaded the entire length of its shank that usually has a recessed drive type.