Abstract: An interchangeable core assembly for a lock core assembly capable of being flush mounted in a door including a housing, a lock insert mounted in the housing, a lock core mounted in the housing adjacent to and cooperative with the lock insert, a thumb-turn assembly mounted in the non-cylindrical housing coaxial with the lock core, a first offset cam mounted on the thumb-turn assembly for rotation therewith, and a second offset cam mounted on the lock core for rotation therewith. The barrel of the lock core assembly is unobstructed by locking train components such that the lock core assembly extends completely through the latch assembly when installed therein. The lock core assembly is secured to the latch assembly without threads and a means to remove/replace the thumb-turn component is provided.