Hillman 1/4 in. X 3/8 in. Internal Hex Socket-Head Set Screw (20-Pack)

A set screw is a type of screw generally used to secure an object within or against another object. Set screws are most often headless, meaning that the screw is fully threaded and has no head projecting past the major diameter of the screw thread. The set screw passes through a threaded hole in the outer object and is tightened against the inner object to prevent it from moving relative to the outer object.