Locks

Claim 1

IN A LOCK, A HOUSING HAVING AN OPENING THEREIN, A KEY PLUG MOUNTED IN SAID OPENING FOR MOVEMENT BETWEEN LOCKING AND UNLOCKING POSITIONS AND HAVING A KEYWAY, SAID HOUSING AND SAID KEY PLUG HAVING TUMBLER HOLES THEREIN WHICH ARE ALIGNABLE AND FORM A TUMBLER BORE COMMUNICATING WITH SAID KEYWAY, A SERIES OF PIN-TUMBLERS SLIDABLE IN SAID BORE TO RELEASE POSITION WHEREIN MOVEMENT OF SAID 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 PIN-TUMBLERS, SAID SERIES OF PIN-TUMBLERS INITIALLY INCLUDING A TEMPORARY PIN-TUMBLER OF A LENGTH TO PERMIT MOVEMENT OF SAID SERIES OF PIN-TUMBLERS 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, SAID TEMPORARY PIN-TUMBLER BEING SMALLER IN DIAMETER THAN OTHER PIN-TUMBLERS IN SAID SERIES AND MOVED INTO THE TUMBLER HOLE IN SAID HOUSING AND ADJACENT SAID KEY PLUG WHEN SAID SECOND KEY IS INSERTED INTO SAID KEYWAY, SAID KEY PLUG HAVING A RECESS THEREIN MOVABLE INTO REGISTER WITH THE TUMBLER HOLE IN SAID HOUSING UPON MOVEMENT OF SAID KEY PLUG BY SAID SECOND KEY, SAID RECESS BEING OF A WIDTH SUBSTANTIALLY EQUAL TO THE DIAMETER OF SAID TEMPORARY PIN-TUMBLER AND OF A DEPTH TO RECEIVE SAID TEMPORARY PIN-TUMBLER, WHEREBY SAID TEMPORARY PIN-TUMBLER IS REMOVED FROM SAID SERIES OF PIN-TUMBLERS IN SAID RECESS TO THEREBY PROVIDE A NEW SERIES OF PINTUMBLERS IN SAID BORE, SAID NEW SERIES OF PIN-TUMBLERS BEING 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 PREVENTING OPERATION OF SAID KEY PLUG BY SAID FIRST KEY AFTER REMOVAL OF SAID TEMPORARY PIN-TUMBLER.