Installing an inside cylinder on an existing mortise lock can be frustrating to center correctly. The HIT-21 will make the job fast, accurate and easy. You don’t even have to take the mortise lock out of the door. Just remove the outside cylinder, thread the HIT-21 into the mortise case until it contacts the mortise cavity on the opposite side. Next drill a pilot hole, then come from the outside in with a hole saw. Nothing could be easier! The HIT-21 is machined from steel with a hardened steel core for longevity. It is also supplied with a drill blank for use in your hole saw.