"A Grub Screw/set screw is a type of screw generally used to secure an object within or against another object. Grub Screw also called a set screw.
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.
A hex key or Allen key is a tool of hexagonal cross-section used to drive bolts and screws that have a hexagonal socket in the head (internal-wrenching hexagon drive).
The most common examples are securing a pulley or gear to a shaft."