What's the noun for bolthead? Here's the word you're looking for.
bolt
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.
A sliding pin or bar in a lock or latch mechanism.
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.
(military) A sliding mechanism to chamber and unchamber a cartridge in a firearm.
A small personal-armour-piercing missile for short-range use, or (in common usage though deprecated by experts) a short arrow, intended to be shot from a crossbow or a catapult.