A commercial lock is defined by two things: the lock function (how it latches, what keeps it closed) and the cylinder type (what accepts the key and operates the latch). The cylinder is the part that gets rekeyed, master keyed, or upgraded to a restricted keyway. Understanding the cylinder type matters because it determines what the lock can do — whether it can be master keyed, whether it can be swapped quickly for rekeying, and how it fits into a building’s overall key system.
Mortise Cylinder
A mortise cylinder threads into a mortise lock body — a lock that’s mortised (recessed) into the edge of the door. The mortise lock body contains the latch bolt, the deadbolt (on some models), and the mechanism that connects the cylinder to the latch. The cylinder itself is a threaded brass cylinder that screws into the lock body from the face of the door.
Mortise locks are the standard for heavy commercial doors — steel doors, fire-rated doors, and high-traffic entrances. They’re more secure than cylindrical locks because the lock body is larger, the latch bolt is heavier, and the mounting is more robust. The cylinder can be replaced or rekeyed without removing the lock body — it unscrews from the front.
Mortise cylinders are threaded, which means they have to be the correct length for the door thickness. Too short and the cylinder doesn’t reach the lock body. Too long and it protrudes past the door face, creating a lever point for a wrench attack. The correct length is measured to the door thickness plus the trim ring.
Manufacturers we install: Schlage (L-series mortise locks), Sargent. Both use standard mortise cylinders that can be pinned to a master key system or upgraded to Medeco or Mul-T-Lock restricted keyways.
Rim Cylinder
A rim cylinder mounts to the surface of the door — it sits on the outside face, held in place by a retaining ring and two machine screws that pass through the door to a mounting plate on the inside. The cylinder operates a rim lock or a rim exit device (panic bar) on the inside surface of the door.
Rim cylinders are the standard for exit devices. A Von Duprin 99 series exit device uses a rim cylinder on the outside that retracts the latch when the key is turned. The rim cylinder is also used on surface-mounted rim locks — the kind often found on apartment building entrance doors and rear commercial doors.
Rim cylinders are easy to swap. The retaining ring unscrews, the cylinder pulls out, and the new one drops in. This makes them ideal for buildings that need to rekey frequently — the cylinder can be exchanged in under a minute per door. Rim cylinders are also the standard format for restricted keyway upgrades: a Medeco or Mul-T-Lock rim cylinder replaces the existing cylinder without changing the lock body or exit device.
Key-in-Knob (Cylindrical) Cylinder
A key-in-knob cylinder — also called a cylindrical lock cylinder — is built into a cylindrical lockset (Schlage D-series, Kwikset commercial). The lock body is bored through the door: two holes, one for the cylinder and one for the latch bolt. The cylinder interfaces with the lock body through a tailpiece that turns the latch.
Cylindrical locks are the workhorse of commercial interior doors — office doors, storage rooms, restroom doors. They’re less expensive than mortise locks and faster to install, but they’re also less secure. The latch bolt is smaller, the lock body is lighter, and the cylinder is integrated into the knob or lever rather than being a separate component.
The cylinder in a cylindrical lock can be replaced — it’s called a “removeable core” in some models — but it’s more involved than swapping a rim cylinder. On a Schlage D-series, the cylinder is accessed by removing the inside rose (the trim plate behind the inside knob), which requires removing the knob first. On interchangeable core versions, the core pulls out with a special control key.
Interchangeable Core (IC)
An interchangeable core is a cylinder design that allows the entire pin tumbler assembly to be removed and replaced without disassembling the lock. The core is held in place by a retaining clip. A special “control key” is inserted, the retaining clip releases, and the core slides out. A new core slides in, the control key is removed, and the lock is rekeyed.
The advantage is speed. A building with 50 doors on an IC system can be rekeyed by one person in under an hour — pull the old cores, insert the new cores, done. No tools beyond the control key. No removing lock bodies, no unscrewing cylinders, no taking apart the door.
IC systems come in two formats:
Small format — the original design, used on Schlage and other cylindrical locks. The core is smaller and fits inside a standard cylindrical lockset.
Large format — a bigger core used on mortise locks and rim cylinders. The large format core is more robust and is the standard for commercial IC systems on heavy doors.
IC systems are specified by keyway: SFIC (Small Format Interchangeable Core) is a generic standard that’s compatible across multiple lock manufacturers. LFIC (Large Format Interchangeable Core) is typically manufacturer-specific.
Which Cylinder Type for Which Application
- Heavy commercial doors, fire-rated doors, main entrances: Mortise lock with a mortise cylinder. Most secure, most durable, most serviceable.
- Exit devices (panic bars): Rim cylinder on the outside. Standard for all rim exit devices.
- Interior office doors, storage rooms: Cylindrical lock (key-in-knob/lever). Adequate security, lower cost.
- Buildings that rekey frequently or have high turnover: Interchangeable core (IC). Fastest rekeying, lowest labor cost per rekey.
Restricted Keyway Upgrades
Every cylinder type discussed above — mortise, rim, cylindrical, and IC — is available in Medeco and Mul-T-Lock restricted keyway versions. The upgrade replaces the cylinder or core while keeping the existing lock body, exit device, or lockset. The door prep doesn’t change. The hardware stays the same. Only the keyway changes.
This is how a building upgrades from standard keys to restricted keys without replacing every lock on every door. The Medeco or Mul-T-Lock cylinder drops into the existing hardware, the new keys are cut to the system’s pinning chart, and the building’s key control is immediately upgraded.
Pro Locksmith LLC is an authorized dealer for both Medeco and Mul-T-Lock. We upgrade existing commercial lock systems to restricted keyways throughout Broward County and Miami-Dade. Licensed and insured. Flat-rate pricing quoted up front. Employees, not subcontractors.
For a cylinder evaluation or restricted keyway upgrade, call Pro Locksmith LLC at (954) 406-8266.
Sources
- ANSI/BHMA A156.2, Bored and Preassembled Locks & Latches (cylindrical locks)
- ANSI/BHMA A156.13, Mortise Locks
- Medeco Security Locks Product Catalog
- Mul-T-Lock 2016 Product Catalog