These Socket Head Cap Screws by Prime-Line Products are constructed of steel and come in a black oxide-coated finish. Their protective coating makes them the ideal corrosion-resistant fastener for use on a variety of projects. The head cap screws have cup points that produce a thin edge that digs into hard surfaces for a secure hold. Rounded head has splined outer circumference with internal hex drive. Use an Allen wrench (hex key) to secure with required torque as needed. Length is measured from underneath the head to the base of the cup point.