What does a dead latch plunger do?
Also asked, how does a dead latch work?
The purpose of the deadlatch is to prevent the latch from being pushed back with a knife or credit card when the door is closed. When cylindrical locks are used with on doors without electric strikes, the deadlatch rests on the metal strike plate that is mounted on the door frame.
In respect to this, why does my door latch stuck?
A sticking door latch might require some lubrication, or it might be jamming against the strike plate on the door jamb. If the latch bolt doesn't move and is fully extended, the issue is with the strike plate. If the latch bolt moves, it is sticking in the door knob and requires some disassembly to fix.
The end of the cylinder is the "latch bolt" (more simply known as the "latch"), which protrudes into a space carved out of the door frame, and which prevents the door from being opened if the knob is not turned. The plate on the front edge of the lock where the latch bolt protrudes is called the faceplate.