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Yes, you can replace a mortise lock with a cylindrical lock, but it is a door-prep job, not a hardware swap. The door edge has a large rectangular mortise pocket, while a cylindrical lock needs a 2-1/8 in cross bore and a 1 in edge bore. You fill or cover the pocket (a conversion or filler plate covers the cut-out), bore the new holes, and fit the latch. Do not do this on a labeled fire door. When does converting from mortise to cylindrical make… Read more