Cylindrical vs Mortise Locks: Which Commercial Lock Is Right?
, by United Doors and Locks, 3 min reading time
A cylindrical lock is carried between two roses; a mortise lock sits in a pocket in the door edge. How that changes cost, durability, functions and install.
Cylindrical and mortise locks do the same job by different means. A cylindrical lock is a mechanism carried between two roses through holes bored in the door face. A mortise lock is a steel case set into a pocket cut in the door edge. That structural difference drives cost, durability, function range, and how hard the thing is to install.
The two preparations
Cylindrical. A 2-1/8 inch cross bore through the door face and a 1 inch bore into the edge for the latch. These are the standard preps on virtually every commercial door made, which is why a cylindrical lock can be fitted or swapped in well under an hour with a boring jig.
Mortise. A rectangular pocket routed into the door edge, roughly 1 inch wide by 6 inches tall by 4 inches deep, plus face holes for the trim and spindle. It requires either a factory prep or a mortising machine on site, and cutting it wrongly is not something you can undo.
If you are retrofitting existing doors, this paragraph may settle the decision on its own.
Durability
Mortise locks are tested to a higher standard because there is more metal doing the work. ANSI/BHMA A156.13 rates Grade 1 mortise locks at 1,000,000 cycles. A156.2 rates Grade 1 cylindrical locks at 800,000. In service the gap is wider than those numbers suggest, because a mortise lock case resists the lever-hanging and door-slamming abuse that eventually loosens a cylindrical lock's roses.
The ML1300 Series Cortland mortise lock is a representative Grade 1 mortise specification. The LC1200 Series is its cylindrical equivalent — Grade 1, 800,000 cycles, UL listed for three-hour fire doors — and for a great many openings it is entirely sufficient.
Function range
This is the mortise lock's real advantage and it is often overlooked. Because the case is large, a mortise lock can hold a latch bolt and a deadbolt operating independently, plus auxiliary features that cylindrical locks cannot accommodate:
- Separate latch and deadbolt in one lock case, with a single strike prep.
- Dormitory and hotel functions where the deadbolt overrides key access.
- Vestibule, apartment entrance, and store door functions with complex key logic.
- Integrated request-to-exit switches and latch monitoring for access control.
If the schedule calls for a function you cannot find in a cylindrical catalogue, that is usually the reason.
Cost, honestly
A Grade 1 mortise lock costs more than a Grade 1 cylindrical, and the mortise prep adds labour on top. Where the mortise pays back is on high-traffic openings over a building's life, where a cylindrical lock may be replaced twice in the same period. Where it does not pay back is on the dozens of quiet interior doors that make up most of any schedule — and specifying mortise locks there is a common way to inflate a hardware budget without improving the building.
How to decide
Specify mortise for: main entrances, high-traffic corridors, doors requiring a deadbolt and latch together, complex key functions, high-security openings, and anything where a lock failure is a serious problem.
Specify cylindrical for: offices, classrooms, storerooms, restrooms, and the general run of interior doors — at Grade 1 like the LC1200 where traffic is real, at Grade 2 like the LC2400 or LC2600 where it is light.
Retrofit work pushes hard toward cylindrical unless the doors already carry a mortise prep. New construction removes that constraint, because either prep can be specified at the factory for the same labour.
One detail on the strike
Mortise locks use an ANSI strike; cylindrical latches may use either an ANSI or a T-strike depending on the frame prep. Mixing them is a frequent source of doors that will not latch cleanly. Confirm the frame prep before ordering, not after — a strike is cheap and a reworked frame is not.
Send us the opening schedule with traffic levels and required functions and we will mark cylindrical or mortise against each line.