Birds Patented 1790

The peculiarity of this lock consists in the levers and springs being attached to the bolt, and moving with it, so that the bolt, the levers, and the springs, in locking and unlocking, all move together, and the stump which in other locks is generally fixed in the bolt, is, in this lock fixed to the plate.
Another feature is the "grate" through which the steps of the key bit have to pass to reach the bolt and the levers.