Mortise locks and locksets

Mortise locks 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.

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 functions 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. The main makers share a 2-3/4 inch backset, but space the lever and cylinder holes differently, so the replacement is like for like unless the door is re-drilled.
• Handing. Most Sargent 8200 functions reverse in the field; a few are handed at the factory.
• Trim and cylinder. The outside trim is a lever or knob with a rose or an escutcheon, and the cylinder is a mortise cylinder whose cam has to suit the case.

Mortise lock vs cylindrical lock: how they differ and what has to match

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. If it takes an SFIC or LFIC interchangeable core, the core alone comes out with a control key.

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