Socket Cap Screws
Knurled Head Cap Screws with an Internal Hex Allen Drive
A socket cap screw is a fastener driven with a socket wrench, and are knurled. A socket cap screw, also known as a socket head cap screw, socket screw or Allen socket bolt, is a type of cap screw with a cylindrical head and hexagonal drive hole. The term socket head cap screw typically refers to a type of threaded fastener whose head diameter is nominally 1.5 times or more that of the screw shank (major) diameter.