Abstract: A lock apparatus includes a housing having a cylindrical bore formed therein and a cam rotatably mounted in the housing. A cylindrical sleeve having a notch formed therein rotatably mounts in the bore of the housing. A cylinder core inserts into the sleeve and engages the cam. The core including multiple tumblers and the housing has a corresponding number of drivers biased toward the bore and engaging the tumblers through the notch and aligned along the periphery of the bore when a proper key is inserted. When the sleeve is rotated, the drivers are captured in their bores, allowing the core to be easily removed without a tube or special tools and providing for simple rekeying.