n A (usually) metal fastener consisting of a cylindrical body that is threaded, with a larger head on one end. It can be inserted into an unthreaded hole up to the head, with a nut then threaded on the other end; a heavy machine screw.
n A bar of wood or metal dropped in horizontal hooks on a door and adjoining wall or between the two sides of a double door, to prevent the door(s) from being forced open.
n A sliding mechanism to chamber and unchamber a cartridge in a firearm.
n A shaft or missile intended to be shot from a crossbow or a catapult, especially a short, stout arrow.