ASTM A574 socket head cap screws (also known as Allen head screws) have a cylindrical head with a flat chamfered top surface, knurled cylindrical sides and hexagonal recess. The ASTM A574 specification covers the complete requirement for quenched and tempered high strength alloy steel hexagon socket head cap screws. Dimensional specifications are governed by ASME B18.3. Socket Head Cap screws supply greater tensile strength than equivalent hex head cap screws, while requiring less surface area to counterbore.These fasteners are commonly used in applications in which it is necessary to recess the head of the fastener, as well as applications where space limits the size of the head, and the tool that drives the fastener. Thread lengths listed are minimum thread lengths, actual thread length may be longer.