Key takeaways
- The two types are graded under different ANSI/BHMA standards (A156.2 for bored locks, A156.13 for mortise locks). Look at the grade and the door's use, not the type alone.
- Changing type is door work. Mortise to cylindrical leaves an empty pocket to fill or cover; cylindrical to mortise means cutting one, often impractical on a steel door.
- Don't cut, bore, fill or cover a lock prep on a fire-labeled door yourself.
- Your keys can usually carry over if the new lock takes a cylinder with the same keyway, the shape of the slot the key slides into.
First distinction
The difference is the hole in the door
A cylindrical lock is installed through two round holes. A large hole, called the bore, goes through the face of the door and holds the lock body and the levers. A smaller hole in the door edge holds the latch. The trade also calls this a bored lock, and a door supplier may call it a 161 lock.
A mortise lock is a flat steel case, roughly the size of a paperback book, that sits in a pocket (the mortise) cut into the door edge. The lever and key cylinder reach it through smaller holes in the door faces. A door supplier may call it an 86 lock.
The holes or pocket cut into a door for its lock are called the prep.
For the parts, functions and common problems of a mortise lock, see the commercial mortise lock guide. Know the maker of your lock? See Schlage L9000 mortise locks for that series.
| What to compare | Cylindrical (bored) lock | Mortise lock |
|---|---|---|
| How it mounts | Through a round bore in the door face, clamped between the two trim pieces, with a latch in a smaller edge hole | In a deep pocket in the door edge, fastened through a tall edge plate, with trim attached through the faces |
| Deadbolt | Not part of the lock. A deadbolt is a separate lock with its own bore above the lever | Can be in the same case as the latch. On many functions the inside lever pulls back the latch and the deadbolt together |
| Replacing it with the same type | The new lock has to suit the backset (the distance from the door edge to the center of the bore) and the door thickness | The new case has to fit the existing pocket and edge plate, and the trim holes in the door faces have to line up. These differ between makers |
Ten-second check
How to tell which lock you have
Open the door and look at its edge first, then at the face.
If yours matches neither, the commercial lock types guide covers the other kinds.
1. The edge plate
A plate about the size of a matchbox with one latch in it points to a cylindrical lock. A plate several times taller than it is wide points to a mortise lock. It often has a latch, a square deadbolt, or both.
2. The key cylinder
On a cylindrical lock the key usually goes into the lever or knob itself. On a mortise lock the cylinder usually sits in the door face above the lever, as a separate round part or in a long trim plate.
3. The exceptions
Trust the edge over the trim: a long trim plate on the face doesn't prove a mortise lock, because some cylindrical locks wear one. A deadbolt above a lever, each with its own small edge plate, is two bored locks. A push bar across the door is an exit device, a third kind of hardware, even when its latch is a mortise case in the edge.
Grades
Both types are graded, under different standards
Many ANSI/BHMA standards grade products 1, 2 or 3, with Grade 1 the highest. Bored locks are covered by ANSI/BHMA A156.2 and mortise locks by ANSI/BHMA A156.13. Under each standard, a Grade 1 lock has to pass a test of one million cycles of opening and closing.
Each grade is set by the benchmarks in its own standard, so it doesn't tell you how a Grade 1 cylindrical lock compares with a Grade 1 mortise lock.
For a busy door, ask for the grade and the standard it was tested to.
Choosing
Which lock suits which door
On an existing door, start with the prep it already has: a worn lock is usually best replaced with the same type, normally the simplest route because nothing in the door has to change. The rows below matter most for a new or replacement door.
Whether a door may have a separate deadbolt depends on the door's use.
See commercial lock functions explained for what each function does from each side of the door.
| Your door | Usual fit | Why |
|---|---|---|
| Interior door with ordinary traffic | Cylindrical | Either type can suit; the prep the door already has is usually the place to start |
| Entrance or other door that takes heavy use or abuse | Either type, at the grade the door's use calls for | Ask for the grade first, then check that the door and the strike are sound |
| A door where you want latch and deadbolt on one lever | Mortise | One case can hold both. With bored locks, that takes an interconnected lock, which links a separate latch and deadbolt |
| Thin door, or one with a narrow frame around glass | Depends on the door | A mortise pocket needs enough thickness and enough solid material beside the glass. Measure before choosing |
Converting
What changing from one type to the other involves
Before anything else, look for a fire label, usually on the hinge edge, though it can be elsewhere. If there is one, don't do any of the work below yourself; see the next section.
A conversion makes more sense than a like-for-like swap when the lock you need isn't made in the type you have.
Mortise to cylindrical
Taking the mortise lock out leaves an empty pocket: a tall slot in the edge and holes in the faces. A new round hole is drilled for the cylindrical lock. The pocket is filled or supported so the door doesn't crush when the new lock is tightened. A filler plate closes the slot in the edge and gives the latch a place to sit, and a wrap plate, a metal sleeve that folds around the door edge and both faces, covers the old holes and stiffens the area.
Cylindrical to mortise
A pocket has to be cut into the door edge. On a solid wood door that is routine work with the right jig, if the door is thick enough and solid at the lock. The old bore may need a long trim plate or wrap plate to cover it.
On a hollow metal door
A steel door has a lock reinforcement, a plate or formed shape fixed inside the door that the lock fastens to. It is usually made for one prep. Cutting a mortise pocket into a door reinforced for a bored lock is often impractical, and a replacement door ordered with the right prep is usually the cleaner answer.
What a plate changes
A wrap plate adds thickness at the door edge, so the gap between door and frame has to allow for it. Plates are made for particular cutouts, backsets and door thicknesses, so measure first.
Fire doors
Fire-rated and labeled doors
If there is a fire label, or a painted-over plate where one would be, treat the door as rated. A rated door is listed as an assembly with its hardware, so an empty pocket or a new bore can affect the rating.
That text is a steel door industry guideline. Wood fire doors have their own listings, so ask the door's maker or its labeling agency. A plate sold for ordinary doors is not necessarily approved for a rated one. Don't cut, bore, fill or cover a prep on a labeled door yourself. See the fire-rated door requirements guide for the opening as a whole.
| Your door | In plain words | What the guideline text says |
|---|---|---|
| A fire-labeled steel door or frame that needs a field modification | On a labeled steel door or frame, the maker contacts the agency that tested or listed it and describes the change. The modification may be performed if that agency finds it does not affect the opening's integrity and fire protection and gives written authorization | "If the product or component requires a field modification, the testing / listing agency that the product or component was listed with shall be contacted by the manufacturer and provided with a description of the proposed modification. If the agency determines that the modification does not affect the integrity and fire protection capabilities of the opening and provides written authorization, then field modifications may be performed." |
Either way
What stays the same: the strike and the keys
The strike is the metal plate on the frame that the latch goes into. A new lock's latch may sit at a different height, and a mortise deadbolt needs its own opening, so expect the strike to be checked, and often replaced, with any change of type.
The two types often take differently shaped cylinders, but a locksmith can usually set up a new cylinder to your existing key if it is made in the same keyway.
Restricted keyways are the usual sticking point, because those cylinders normally come through the supplier that controls the keyway. Say so early if your keys can't be copied at a hardware store.
See the strike plates guide for matching a strike to a frame, and the rekeying and master key guide for keys and cores.
Who does what
What to leave to a locksmith, and what to tell them
Tightening loose trim screws and, on a door with no fire label, swapping a cylindrical lock for the same model are fair game. These jobs are not:
When you call, say which type is on the door now, which you want and why. Give the door material and thickness, the backset, and whether the door or frame has a fire label. Say which way the door swings, since some locks are built for one handing (left-hand or right-hand door), and whether your keys have to keep working. Photos of the door edge, both faces and the strike answer most other questions.
- Any change of lock type, in either direction
- Anything on a fire-labeled door or frame beyond tightening a screw
- Cutting or drilling a steel or aluminum door, or a door with glass near the lock
- Electrified locks, and any lock wired to an access control system
- Keeping a master key system or a restricted keyway intact across a lock change
If you need the lock changed
Elwin Security installs, repairs and replaces mortise and cylindrical locks, and converts doors between mortise and cylindrical lock preps, for commercial and multifamily properties in the San Francisco Bay Area. Calls are answered 8:00 AM-8:00 PM daily at (408) 539-0535.
Common questions
Mortise and cylindrical lock questions
What is the difference between a mortise lock and a cylindrical lock?
Where it mounts. A cylindrical lock goes through a round bore in the door face; a mortise lock is a case set into a pocket in the door edge and can hold a latch and a deadbolt together.
Is a mortise lock more secure than a cylindrical lock?
Not by type alone. Each type is covered by its own ANSI/BHMA standard, and the grade, the cylinder, the strike and the door all matter.
Can I replace a mortise lock with a cylindrical lock?
On many doors without a fire label, yes, with a filler or wrap plate over the old pocket and a new bore. On a fire-labeled door, don't make that change yourself.
Sources and further reading
These sources back up the general guidance. Your building and the people who approve the work decide the details for your doors.
- Builders Hardware Manufacturers Association: Product Grade Levels
- Builders Hardware Manufacturers Association: A156.2-2022 Locks and Latches (Hardware Highlights)
- Builders Hardware Manufacturers Association: A156.13-2022 Mortise Locks (Hardware Highlights)
- Steel Door Institute: SDI 118-21, Basic Fire Door, Fire Door Frame, Transom/Sidelight Frame, and Window Frame Requirements
- Steel Door Institute: SDI 134-26, Glossary of Terms for Hollow Metal Doors and Frames