Locks

Claim 1

IN A LOCK, A HOUSING, A UNITARY KEY PLUG MOUNTED IN SAID HOUSING FOR MOVEMENT BETWEEN LOCKING AND UNLOCKING POSITIONS AND HAVING A KEYWAY, THERE BEING AT LEAST ONE TUMBLER BORE IN SAID HOUSING AND SAID KEYPLUG COMMUNICATING WITH SAID KEYWAY, A SERIES OF TUMBLER ELEMENTS MOVABLE IN SAID BORE TO A RELEASE POSITION WHEREIN MOVEMENT OF THE KEY PLUG TO UNLOCKING POSITION IS PERMITTED, A FIRST USED KEY AND A SECOND CHANGE KEY INSERTABLE INTO SAID KEYWAY AND BITTED FOR COOPERATION WITH SAID SERIES OF TUMBLER ELEMENTS, THE INITIAL COMBINATION OF SAID SERIES OF TUMBLER ELEMENTS BEING SUCH THAT SAID SERIES OF TUMBLER ELEMENTS IS MOVED TO A RELEASE POSITION WHEN EITHER SAID FIRST KEY OR SAID SECOND KEY IS INSERTED INTO SAID KEYWAY SO THAT SAID KEY PLUG IS OPERABLE BY EITHER OF SAID KEYS, AND A RECESS IN SAID UNITARY KEY PLUG COMMUNICABLE WITH SAID BORE FOR RECEIVING AND EFFECTING PERMANENT REMOVAL OF AT LEAST ONE OF SAID TUMBLER ELEMENTS FROM SAID BORE THE FIRST TIME SECOND KEY IS USED TO OPERATE SAID KEY PLUG TO THEREBY PROVIDE A PERMANENT NEW SERIES OF TUMBLER ELEMENTS IN SAID BORE, THE COMBINATION OF SAID NEW SERIES OF TUMBLER ELEMENTS BEING SUCH THAT SAID NEW SERIES OF TUMBLER ELEMENTS IS MOVED TO A LOCKING POSITION, WHEREIN MOVEMENT OF SAID KEY PLUG TO UNLOCKING POSITION IS PREVENTED, WHEN SAID FIRST KEY IS INSERTED INTO SAID KEYWAY THEREBY PERMANENTLY PREVENTING OPERATION OF SAID KEY PLUG BY SAID FIRST KEY AFTER THE INITIAL SERIES OF TUMBLER ELEMENTS HAS BEEN CHANGED.