A set screw is a type of screw generally used to secure an object within or against another object. They are usually headless which means the screw is fully threaded and has no head projecting past the major diameter of the screw threads. Set screws are almost always driven with an internal-wrenching drive, such as a hex socket, 6 lobe, square socket, phillips or slot. They are used in applications which require the set screw to pass through a threaded hole in the outer object and tightened against the inner object to prevent it from moving.