A socket cap screws are machine screws with a cylindrical barrel shaped head containing a hexagonal socket. The head has a smaller diameter than most other machine screw heads, typically just 1.5 times the nominal thread diameter. Socket cap screws may also be referred to as a socket head cap screw, a cap head socket screw or hex socket head screw. Fastening for these components requires no external clearance, which is typical of screws such as a hex head for it to accept a spanner or socket. These properties mean that socket head cap screws are well suited for use within confined spaces. Socket cap screw are often used with the head recessed within a counterbored hole, leaving the end of the head flush with the surface of the part being fastened. This produces a clean appearance and leaves no protrusions that could catch or be damaged, making them popular in sporting equipment such as bicycles.
