Hex Set Screws is the term used for what is effectively a fully threaded hexagon head bolt which doesn't contain a shank (plain or unthreaded section). Although set screws can be used with a nut, typically they will be used in applications where they are threaded directly into something containing a matching pre-threaded hole such as a machinery component. The hex head set screw is designed to be tightened/removed with a suitably fitted wrench, spanner, socket or other hex driver.