When mortise cylinders and lock cases are new they screw together without a problem. However, 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 Tap can easily be twisted into a stripped lock case cutting new useable threads into an otherwise ruined lock