Socket screws are a type of screw designed and manufactured with a hexagonal (hex) internal drive built into the head. As such, they are intended to be tightened and loosened with an Allen wrench or hex key, as opposed to a traditional screwdriver. A socket head cap screw features a cylindrical head and a hexagonal recess. This specialised drive requires a hex wrench or Allen key to tighten or loosen the screw.