That part of the lock mechanism containing a square hole to admit the spindle (to which door handles are attached) which pulls back the springbolt when turned.
The part of a wardrobe lock or spring latch that pulls the latch into the body of the lock allowing the door to open. There is a square hole in the follower to allow a spindle attached to a knob or handle to go in. When the knob is turned this turns the follower which opens the latch.
That part in a firearm which, through the action of a spring, forces a cartridge or cartridges to move.