Abstract: A pin assembly includes a spring held in compression inside a case by a thermal fuse located at the back end of the pin. The fuse is thermally activated to collapse, which allows the back end of the pin to move forward. The spring drives the front end of the pin out of the case into latching engagement between a first object, such as a fire door, and a second object, such as a floor or a doorframe. The fuse and spring are located on opposite sides of a restrictive opening at the back end of the case. The fuse is preferably cylindrical, surrounds the back end of the pin and is provided with holes oriented perpendicular to the cylindrical axis of the fuse forming a web. The holes weaken the fuse and cause it to collapse in a controlled manner at the desired activation temperature.

Abstract: This invention provides a thumb-piece door latch mechanism which has ergonomic features, is modular and can be used with any escutcheon, can be used with all type locks, and which in the locked door mode provides greater resistance to abusive attack of the door latch mechanism and makes the thumb-piece and latch mechanism more durable and less susceptible to vandalism. The thumb-piece moves linearly up and down and is connected to a thumb-piece guide plate which likewise moves up and down when the thumb-piece is moved. A permissive spring having one end connected to a spindle turn plate and the other end connected to the guide plate moves a rotatably mounted spindle, which in turn rotates a spindle tail and a latch connected to the spindle tail. The permissive spring provides greater resistance to abusive attacks of the door lock and mechanism.