Mortise lockset (ANSI/BHMA A156.13)
The commercial workhorse: a large case in a pocket in the door edge, with a huge function catalogue (passage, entry, classroom, storeroom, exit). Retrofit means understanding the function, not just the dimensions.
Also called: Mortise lock · Commercial mortise
Anatomy
- Large mortise case, typically 4 in or 4-3/4 in tall
- Cylinder mounted separately in the case
- Trim (lever or knob) on both faces
- Function-specific cams and dogging mechanisms
Parameters to measure
Measure in this order: Lock case width × height × depth → Backset (Dornmaß) → Centre distance, spindle-to-cylinder (Entfernung / PZ) → Door thickness
| Parameter | Typical values | Tolerance that still fits | How to measure |
|---|---|---|---|
| Lock case width × height × depth | Case height 4 in (102 mm) or 4-3/4 in (121 mm) | — | Remove the case and measure the pocket. |
| Backset (Dornmaß) | 2-3/4 in (70 mm) or 2-1/2 in | — | Door edge to the cylinder centre. |
| Door thickness | 1-3/4 in (45 mm) typical for commercial doors | — | At the case. |
| Centre distance, spindle-to-cylinder (Entfernung / PZ) | Function-dependent; record the actual spindle-to-cylinder value from the case | None | With the trim off, measure the case from the spindle centre to the cylinder centre. |
Retrofit architectures that work
- Full lock replacement on the same footprint — The old lock case is removed and a smart lock with the same footprint takes its place. This is the dominant approach in East and Southeast Asia, where push-pull digital locks replace mortise sets on HDB, condo and apartment doors.
- Motor replacing the interior handle — The interior lever or knob is replaced by a motor unit that drives the 8 mm spindle directly. The outside keeps the original key cylinder and handle. This is the cleanest fit for mortise locks where the bolt is thrown by the key and the handle only retracts the latch.
On a door with panic hardware or an access-control reader, the retrofit must not defeat either. Where a reader already exists, an electrified lock (A156.25) is usually a better path than a battery motor.
Related standards
ANSI/BHMA A156.13 · ANSI/BHMA A156.25
Questions
How many cycles does a mortise lock survive?
Allegion lists 1,000,000 for A156.13 Grade 1 and 800,000 for Grades 2 and 3 — an unusual case where the lower grades share a number.