Socket set cap screws have cup points that produce a thin edge that digs into hard surfaces for a secure hold. This fastener is headless and contains an internal hex drive. Use an Allen wrench (hex key) to secure with required torque as needed. Although often used in machinery, they can be found around the home as well to secure window crank handles to window operators or to hold interior door knobs to spindles. Length is measured from the top of the fastener to the base of the cup point.