A plunger type lock construction in which the key receiving face thereof is spaced a critical distance from a portion of a reciprocable plunger which is within the lock body and which is engaged by the key to release locking members extending from the lock body. The lock body has shaped means at its key receiving face which prevents insertion of a key to the proper, lock operating depth in the lock if the end of the key which faces the key receiving face is not shaped so as to receive the shaped means on the lock body. Each lock may have a differently shaped means so that a key which will fit one lock will not fit another lock, but a master key may be provided which will fit all or only a plurality, of such locks.