Socket screws in use in an engine
Socket screws contain a hexagonal socket, or internal drive, in the head. The way to tell if a screw is a socket screw is by the tool required to tighten and loosen it. The general rule of thumb is simple: if you need an allen or hex key, or a special internal wrenching drive, then it can be classed as a socket screw.
Socket screws are known by different names:

Socket head cap screw, or socket cap screw
Hex socket head cap screw, or hex socket screw
Allen socket bolt, or allen bolt
Socket head screws

Socket screws are the preferred screw when bolts and nuts can’t be used. The hex socket means the screw has six stress-bearing sides. Compared to other screws, socket screws of the same size enable you to achieve higher torque and clamping force. This, in turn, allows you to use fewer socket screws than you’d have to install if using other screws.

Fewer pieces of hardware reduce the weight of your finished application. If that’s a priority – think automotive – then socket screws are ideal. Fewer screws needed also reduces your costs and time needed to drill holes and tap into surfaces.