Abstract: A cylinder lock assembly is provided with a cylindrical plug that may be interchanged and used in different exterior body members without changing the exterior body member of the assembly. This is of advantage to eliminate the need to stock a variety of expensive cylinder assemblies for plugs having different keyways or keys with different bitting locations. It is only necessary to maintain a supply of different plugs and keys. Commonality of parts for mortise and rim type locks also reduces inventory required in commercial and institutional establishments.The pin bores in the exterior members and the pin bores in the plugs are located a constant distance away from a selected reference point in the lock assembly and the exposed keyway face of the plugs. As a result, the pin bores in one or more plugs will align with the pin bores in one or more exterior body members so that the plugs may be used with different exterior body members.