Where can you use a socket head cap screw? Socket head cap screws are commonly used in assemblies that do not provide sufficient clearance for a conventional wrench or socket. They have a cylindrical head and internal wrenching features, mostly hexagon socket. That allows them to be used in locations where externally wrenched fasteners are not desirable. They are used for critical vehicle applications, machine tools, tools and dies, earth moving and mining machinery, and a wide range of engineering applications.