Fig. 43
39. Master-Key Locks.—The type of lock known as the master-key lock is generally used for public or office buildings, hotels, and occasionally in the better class of residence work. These locks can be grouped into two classes; namely, the Yale, or cylinder, and the lever-tumbler types, the class first mentioned being the most desirable.
In the lever-tumbler type, illustrated in [Fig. 39], the tumblers, or wards, are so arranged that each lock can be operated only by its particular key, the keys for all rooms being different and non-changeable; all of the locks, however, can be operated by a key made for the purpose, termed a master key. Each lock of this type has two sets of tumblers; one set is operated by its individual key, and the other, being uniform in all locks of the series, is acted on by the master key. Such locks may be obtained either in the cheaper kind, with one tumbler and twelve changes, or in the most intricate styles of hotel locks, with five tumblers and 48,000 changes in one set, and all operated by one master key. The cylinder lock of this type is illustrated in [Fig. 44], which shows a Yale & Towne, mortise, front-door lock.
Fig. 44
40. Details of the Yale Type of Master-Key Locks. The Yale type of cylinder lock, which is illustrated in [Fig. 45 (a) and (b)], is much preferred, on account of the great security it gives and the small key required by it. This lock is made in three systems; namely, the regular, the concentric, and the paracentric, or duplex.
In the regular system, one regular cylinder is controlled by the change and master keys, the pin tumblers being cut in two places, so that the change key brings one set of the abutting planes of the tumbler in alinement with the surface of the cylindrical plug. This plug is arranged so that a separate key is required to operate each lock, the other line of cleavage through the blocks being the same with all locks throughout the series, so that they may be opened with the same key.
