Abstract: A resettable single-barrel single-plug cylindrical two section lock assembly is provided wherever master keying is required. The lock of the invention is intended to be operated and reset by three different keys. One key (#1 key) is used to turn the lock to a position in which it may be reset by either of the other two keys. One of the other two keys (#2 key) operates a first section of the dual lock; and the other of the other of the two keys (#3 key) operates a second section of the lock which is independent of the first section. Either section may be reset by inserting the existing #2 or #3 key into the lock once the lock has been turned by the (#1) key to a predetermined position, and then turning the lock to the reset position, and after the existing key has been withdrawn, turning the lock back to its normal operating position by the new key, either the #2 or #3 keys, depending upon which section of the lock is being re-keyed.

Abstract: A double-barrel double-plug cylindrical lock is provided for hotels, and the like, where changes of occupancy frequently occurs. The lock cylinder is constructed to be of approximately the same size and shape as the prior art lock cylinders, so that the lock of the invention may readily be mounted into existing mortise door hardware to replace existing cylindrical locks. One plug of the lock is intended to be operated by the guests' key; and the other plug is intended to be operated by the maid's key, by an emergency key and by a program key. The guest key may be used to turn the guest plug to a resettable position in which a new guest key may be inserted which sets the guest plug to accept the new key. However, the lock is constructed so that the guest plug cannot be turned to its resettable position unless the emergency key or program key is first inserted in the other plug to turn the other plug to a particular angular position in which the guest plug is able to be turned to its resettable position.

Abstract: A cylindrical lock assembly is provided which is approximately the same size as present-day cylindrical "Mortise" locks, and which can replace present-day locks in the doors of hotels, motels, or other establishments, merely by removing the existing lock cylinders and replacing them by the lock cylinders of the invention. The lock assembly of the invention has a number of internal logic ring members which are mounted tandem to one another in coaxial relationship with the central axis of the lock, and which are replaceable to change the key pattern to which the lock will respond. The lock also includes a plurality of spring-biased tumblers, which are moved longitudinally to mating positions with respect to the various logic ring members when the proper keys are inserted in the lock.