Key takeaways
- Identify hardware in a fixed order: mounting location, then family, then function, then model or series, then voltage or keying.
- The family describes how a lock is built and mounted; the function describes how it behaves from each side of the door.
- A cylindrical lock bores through the door face while a mortise lock lives in a pocket cut into the door edge, and the two preparations are not interchangeable.
- Cylinder formats — key-in-lever, mortise, rim, and interchangeable core — must match on format, keyway, and cam or tailpiece before a replacement will work.
- Exit devices are egress-critical hardware; changes to them belong with qualified installers working to the approved hardware for the opening.
- Record function, dimensions and preparation, handing, finish, rating, keying, and any voltage before approving a replacement order.
Method
How do you identify a lock without taking the door apart?
A commercial opening behaves as one system: door, frame, hinges, latch, strike, closer, and any electrified hardware act together, and the lock is only the most visible part. Identifying the lock correctly matters because every replacement must match the door's existing preparation — the holes, pockets, and reinforcement already cut for it — and a wrong guess turns a simple hardware swap into door surgery.
The reliable method works in a fixed order: mounting location first, then hardware family, then function, then model or series, and finally voltage or keying. Mounting location can be read from a few feet away and narrows the family immediately. Family determines what preparation the door carries. Function describes behavior and is confirmed by operating the door, not by appearance. Model, series, voltage, and keying complete the record a supplier needs to match the part.
Work from coarse to fine and resist jumping straight to a brand name. Two locks from different manufacturers can look identical from the corridor and still differ in chassis dimensions, cylinder format, and door preparation.
First pass
Where does the hardware mount, and what does that tell you?
The first pass never needs a screwdriver. Where a piece of hardware mounts is usually enough to name its family and whether it is mechanical or electrified.
| Hardware | Where it mounts | What you will see |
|---|---|---|
| Cylindrical lock | Bored through the door face; the latch enters from the door edge | A round rose or escutcheon around a knob or lever on each face, with a small separate latch plate on the edge |
| Mortise lock | A large lock case recessed into a pocket in the door edge | A tall rectangular faceplate on the edge, often carrying both a latch and a deadbolt, with trim through-bolted to the faces |
| Exit device | Across the width of the door on the egress side | A push pad or crossbar; latching at the door edge, at the top and bottom of the door, or into a mortise case |
| Surface closer | At the top of the door or frame | A closer body with an arm or track connecting the door and frame |
| Electric strike | In the frame, at the latch or approved bolt location | A frame-mounted keeper with a metal faceplate where the latch lands, usually with low-voltage wiring behind it |
| Electronic lever | Through the door, with reader and locking mechanism integrated | A lever set with a credential reader or keypad and battery or wired power at the door itself |
Five families
Five lock families cover most commercial doors.
Cylindrical and tubular locks
The most common commercial family. The chassis installs through a round bored preparation in the door face, and a separate latch enters from the door edge. Grades and series vary widely — Schlage's ALX series is one Grade 2 example — but the bored prep is the family's signature.
Mortise locks
A large rectangular lock case sits in a pocket cut into the door edge, with trim and cylinder mounted through the faces. Mortise locks such as the Schlage L series concentrate latch, deadbolt, and function control in one case; the edge pocket is a substantial preparation that not every door can accept.
Deadbolts
Bolt-only security with no spring latch. Deadbolts are auxiliary hardware, and their use is limited on many commercial doors: where an opening serves egress, verify that the installed arrangement still releases the way adopted code and the authority having jurisdiction require before adding or keeping one.
Interconnected locks
A lever and a deadbolt linked so one inside motion retracts both. The interconnection exists to preserve single-motion egress while keeping a bolt on the door, which is why the family appears on unit and office entries where a deadbolt is wanted without complicating exit.
Exit devices
A push pad or crossbar across the egress side that retracts the latch under body pressure. Latching style varies by opening — rim, surface or concealed vertical rods, or a mortise case — and because egress performance is central, exit devices are approved-hardware territory rather than a place to improvise.
Second distinction
Family is construction; function is behavior.
The family names the construction: how the lock is built, how it mounts, and what preparation the door carries. The function names the behavior: what each side of the door does when the lock is locked, unlocked, or keyed. A cylindrical lock can be a passage set, a storeroom lock, or an office lock in the same housing — identical from the corridor, completely different in daily behavior.
Never assume function from appearance. Operate the door from both sides, test the key, and record what actually happens before and after any work. Function selection carries its own obligations — free egress from the inside must be preserved wherever it is required — and choosing between passage, privacy, storeroom, classroom, and office functions is covered in the companion guide on lock functions.
Keyed side
Which cylinder format is in the lock, and why does it matter?
The cylinder is the keyed component inside the lock, and it has its own format independent of the lock family. Compatibility is not universal: a replacement must match format, keyway, and cam or tailpiece, and the manufacturer's requirements control.
| Format | Construction | Where it appears |
|---|---|---|
| Key-in-knob / key-in-lever (KIK / KIL) | A raised-bible cylinder with a compact tailpiece | Many bored knob and lever chassis |
| Mortise cylinder | A threaded shell with a rear cam that screws into the housing | Mortise locks, key switches, and specialty housings |
| Rim cylinder | A long tailpiece and mounting plate that through-bolt to the hardware | Surface-mounted hardware and many exit devices |
| Interchangeable core (SFIC / FSIC) | A figure-eight core that a dedicated control key releases from its housing | Properties that rekey by swapping cores rather than servicing individual cylinders |
Authorized work
What are the rules when keys and cylinders change hands?
Cylinders and keys are where lock work touches a property's security posture directly, so the working rules are strict. Cylinder and key work here means authorized work: performed with the owner's or manager's authorization and recorded in the property's key-control records.
- Verify authorization before any cylinder is pulled, rekeyed, or replaced, and keep the work order tied to the specific opening.
- Match keyway and format exactly; a cylinder that threads or seats into the hardware is not automatically compatible with the key system.
- Treat control keys as privileged assets: they release interchangeable cores, so their movement should be logged and their storage controlled.
- Record every key and core issued or returned so the key system's paper trail stays complete.
- Expect a qualified locksmith to decline improvised master pinning; keying changes belong inside the documented key system, not in field guesswork.
- When key system ownership is unclear, the correct move is to stop, secure the keys, and confirm ownership before work continues.
Replacement checklist
What should you record before ordering a replacement lock?
Most wrong-part orders trace back to a photo that showed the trim but not the preparation. Capture the full record before approving a replacement — a supplier can usually match hardware from it without a second site visit.
- Function: how each side of the door behaves, confirmed by operating the door and testing the key rather than by appearance.
- Dimensions and preparation: backset (commonly 2-3/4 inches on commercial doors), bore or mortise-pocket dimensions, faceplate size, and door thickness.
- Handing: which side the hinges are on and which way the door swings, recorded per the manufacturer's handing convention.
- Finish: the existing hardware finish, so the replacement matches the opening and its neighbors.
- Rating: any fire label on the door or frame edge, which limits the replacement to listed, compatible components.
- Keying: cylinder format, keyway, and whether the opening belongs to a master key system.
- Voltage and current for electrified hardware, plus fail-safe or fail-secure behavior, confirmed from the installed equipment rather than assumed.
- Options: lever style, monitoring switches, cylinder overrides, and anything else visible on the unit — photograph both faces, the full door edge, and the frame.
Common questions
Questions about identifying commercial locks
How can I tell a cylindrical lock from a mortise lock without removing anything?
Look at the door edge. A cylindrical lock shows a small latch plate, roughly an inch wide, separate from the trim on the faces. A mortise lock shows a tall rectangular faceplate — often about eight inches — frequently carrying both a latch and a deadbolt. The edge shows the preparation, and the preparation names the family.
Are lock cylinders interchangeable between brands?
No. A cylinder must match on three axes: the format (key-in-lever, mortise, rim, or interchangeable core), the keyway the keys are cut on, and the cam or tailpiece that engages the lock. Two cylinders can look identical and still fail on any of the three. Confirm format and keyway against the installed hardware and the manufacturer's documentation before ordering.
What is an interchangeable core, and why do properties use them?
An interchangeable core is a self-contained, figure-eight-shaped cylinder that a dedicated control key releases from its housing. Properties use small-format (SFIC) and full-size (FSIC) cores because rekeying becomes a quick core swap and one core format can run across many hardware types. The trade-off is that control keys become privileged assets that must be strictly managed.
Can a deadbolt be added to any commercial door?
No. A deadbolt is bolt-only auxiliary hardware, and doors that serve required egress are generally expected to release in a single motion without keys or special knowledge. Whether a deadbolt is permitted depends on the opening's use, the installed hardware arrangement, adopted code, and the authority having jurisdiction — verify before cutting a second preparation into the door.
What should a property manager photograph before calling about a lock replacement?
Photograph both faces of the door with the trim visible, the full door edge showing every faceplate, the strike side of the frame, and any label on the door or frame edge. Add close-ups of manufacturer markings on faceplates and cylinders. Those photographs usually let a supplier or locksmith name the family, likely series, and cylinder format before anyone visits.
Sources and further reading
These references support the general technical guidance. The right answer for a specific opening still depends on the property and the authorities responsible for the project.