3/8-16 x 5/8 Cup Point Setscrew

A set screw or grub screw is a type of screw generally used to secure an object within or against another object, normally without using a nut . The most common examples are securing a pulley or gear to a shaft. Set screws are usually headless (also called blind), meaning that the screw is fully threaded and has no head projecting past the major diameter of the screw thread. If a set screw has a head, the thread will extend all the way to the head (whereas a bolt might have an unthreaded shank between the head and thread)