Abstract: A rotary cylinder assembly for a machine tool is provided that includes a lock check system that locks the work piece to the machine tool chuck and prevents extension and retraction of the work piece in the event of loss of hydraulic or pneumatic pressure. The rotary cylinder assembly includes a shaft end cover coupled between a fluid shaft housing and a cylinder body. The shaft end cover houses the lock check system and includes a number of flow paths that provide for extension and retraction of a piston rod connector housed in the cylinder body in response to fluid pressure supplied from the fluid shaft housing. The shaft end cover and lock check system are configured to allow small diameter cylinder bodies to be coupled thereto while providing the safety and functional features associated with the lock check system.