Socket Head Cap Screws Guide: Allen Screws for Machinery
Socket head cap screws combine a cylindrical head with an internal hex drive. The geometry allows high tool engagement from the top while using less radial space than an external.
Allen vs Torx vs Phillips vs Slotted: Which Screw Drive Is Best?
The drive is the interface between a screw and the tool used to install it. Allen, Torx, Phillips and slotted drives can all be found on metric machine screws, but they behave.