When mortise cylinders and lock cases are new they screw together without a problem. Often times a mortise cylinder is forced out of a lock without loosening the retaining screw. Other times an inexperienced person will force a mortise cylinder into a lock crooked. These actions result in stripping the threads of the cylinder or the lock case itself. The HPC Mortise Cylinder Lock Tap & Die Set was designed to repair this type of damage. The Tap can easily be twisted into a stripped lock case cutting new useable threads into an otherwise ruined lock. The Holding Fixture secures a stripped mortise cylinder in your vise while you use the Die to repair the threads. The Tap and Die are available separately and come complete in a metal storage box.