Abstract: A key-operated lock comprising a housing, a core and a set of pin stacks. The housing has a set of driver chambers and a set of inactive master-pin chambers. Each pin stack comprises pin stack elements, which include a driver and a tumbler. The driver is movably mounted in one of the driver chambers. The tumbler assembly is movably mounted in the core for radial movement relative to the bore in the body. Further, the tumbler assemblies including a plurality of releasably engaged parts movable relative to each other upon disengagement to change a dimension of the tumbler assemblies. Additionally, for at least one of the pin stacks, the pin stack elements further comprise one or more master pins.

Abstract: A plug for a key operated lock is provided with a plurality of bores transverse to the key slot formed through the plug. The bores accept studs which extend into the key slot to delimit the design of key blanks from which keys, fitting the lock, can be constructed. The selection of bores to contain studs permits rapid change of key blank designs for the lock.