Mortise locksets

Mortise locksets for existing openings

A mortise lock is a lock whose case sits in a deep pocket cut into the edge of the door, with the lever trim and the cylinder fitted to that case from each face.

Mortise locks, cases, trim and cylinders for doors already prepared for them, replaced like for like so the new lock fits the pocket and the holes already in the door.

That is why a mortise lock is usually replaced like for like, and why the part number on the old case matters more than on almost any other lock.

How it is specified

• Function. Mortise locks come in the same kinds of function as cylindrical locks, passage, privacy, office, classroom and storeroom, and a mortise case can also throw a deadbolt from the same body.
• Case and door prep. Mortise cases differ in size and backset between manufacturers.
• Handing. Many mortise locks are handed at the factory and cannot be reversed in the field.
• Trim and cylinder. The outside trim is a lever with a rose or an escutcheon, and the cylinder is a mortise cylinder whose cam has to suit the case.

Mortise locksets: cases, functions and trim, the full guide

What usually fails

A lever that sags, or a latch that sticks, is often a worn spring or a tired case rather than the trim. A deadbolt that will not throw is frequently strike alignment. A cylinder that turns hard can be replaced without touching the case.

Photograph the face of the case on the door edge, where the manufacturer and function are usually stamped, and both sides of the trim.