What is a Mortise Cylinder?

A mortise cylinder is a removable lock cylinder that threads directly into a mortise lock body, allowing the cylinder to be installed, replaced, or rekeyed without removing the entire lock. Unlike a rim cylinder, which mounts on the surface of a door, a mortise cylinder screws into a threaded housing recessed into the door itself, giving it a cleaner, more integrated installation.

Mortise cylinders are widely used in commercial buildings and higher-end residential doors, where mortise locks are already the standard hardware because of their strength and durability. Because the cylinder is a separate, interchangeable component, locksmiths can service or upgrade the lock's security without replacing the entire mortise lock body.

How Does a Mortise Cylinder Work?

A mortise cylinder works the same way as a standard pin tumbler cylinder internally, using key pins, driver pins, and springs aligned at a shear line to allow the plug to rotate. What sets it apart is how it's mounted: the cylinder has external threads that screw directly into a matching threaded housing on the mortise lock body, and it's secured in place with a cam and a small set screw accessed through the edge of the door.

When the correct key is inserted and turned, the plug rotates and drives the attached cam, which engages the internal mechanism of the mortise lock to retract the latch or throw the deadbolt. Because the cylinder threads in and out as a single unit, a locksmith can remove and replace it in minutes without disassembling the mortise lock body itself.

How to Change a Mortise Lock Cylinder

Changing a mortise lock cylinder is a straightforward process for anyone with basic locksmith tools:

1. Remove the set screw on the edge of the door that secures the cylinder in place.

2. Unscrew the cylinder counterclockwise from the mortise lock body using a cylinder wrench or by hand, depending on how tightly it's seated.

3. Note the cam position and length before removing it fully, since the replacement cylinder must use a matching cam orientation and length.

4. Insert the new cylinder, threading it clockwise into the mortise lock body until snug, with the cam aligned the same way as the original.

5. Reinstall the set screw to lock the new cylinder in place.

6. Test the key to confirm the latch and deadbolt retract smoothly before closing up the door.

If the replacement cylinder needs to be rekeyed to match an existing key, this should be done with a pinning kit before installation, or by a locksmith at the time of the swap.

How Can I Convert a Mortise Lock to a Cylindrical Lock?

Converting a mortise lock to a cylindrical (bored) lock is possible but requires more than a simple cylinder swap, since the two lock types use different door preparations. A mortise lock body sits inside a rectangular pocket mortised into the door edge, while a cylindrical lock uses round bore holes drilled through the face and edge of the door.

To convert between the two, a locksmith typically needs to:

• Fill and finish the existing mortise pocket in the door edge

• Drill new bore holes sized for the cylindrical lockset

• Install a new strike plate matched to the cylindrical lock's latch

• Fit and align the new cylindrical lock hardware

Because this changes the door's structure rather than just the lock hardware, it's usually done by a professional locksmith or carpenter, and in commercial settings may also need to meet fire code and ADA hardware requirements.

How Much Does a Mortise Lock Cylinder Cost?

Mortise lock cylinder pricing depends on the brand, security grade, and finish. As a general range:

• Standard residential/commercial mortise cylinders: roughly $20–$60

• Mid-grade commercial cylinders (e.g., Schlage, Kwikset commercial lines): roughly $40–$100

• High-security mortise cylinders (restricted keyways, patented key control, SFIC/IC compatible): roughly $80–$250+

Professional installation or rekeying by a locksmith typically adds a labor cost on top of the cylinder price itself. Buying in bulk or through a wholesale locksmith supplier like CLK Supplies generally brings the per-unit cost down for locksmiths servicing multiple doors or running commercial contracts.

Key Components of Mortise Cylinders

A mortise cylinder is made up of several parts specific to its threaded, screw-in design:

• Cylinder housing – the threaded outer shell that screws into the mortise lock body

• Plug – the rotating core containing the pin stack, same as in a standard cylinder

• Cam – attached to the back of the plug, this drives the mortise lock's internal mechanism when the key turns

• Set screw – secures the cylinder in place once threaded into the lock body

• Face cap / trim ring – the decorative finish visible on the door face

• Key pins, driver pins, and springs – standard pin tumbler components that determine which key operates the cylinder

The cam length and cylinder length must be matched to the specific mortise lock body and door thickness for proper installation.

What Are the Common Uses of Mortise Cylinders?

Mortise cylinders are used wherever mortise lock bodies are already installed, including:

• Commercial entry doors and storefronts

• Apartment and multi-family building entry doors

• Hotel doors using mortise lock hardware

• High-end residential doors requiring heavy-duty security

• Doors integrated into master key systems

Because mortise locks are common in commercial and institutional settings, mortise cylinders are a frequent rekeying and replacement job for commercial locksmiths.

Main Characteristics of Mortise Cylinders

Mortise cylinders share several defining traits that distinguish them from rim cylinders:

• Thread directly into a mortise lock body rather than mounting on the surface

• Secured with a set screw accessed through the door edge

• Use a cam to engage the mortise lock's internal latch and bolt mechanism

• Available in various lengths to match door thickness and lock body specifications

• Compatible with standard pin tumbler rekeying using pinning kits

• Often used within interchangeable core (IC) or SFIC systems in commercial buildings

These characteristics make mortise cylinders a precise, hardware-specific component that must be matched correctly to the lock body it's installed in.

Advantages of Mortise Cylinders

Mortise cylinders remain the standard choice for mortise lock hardware for several practical reasons:

• Easy replacement – threads in and out without disassembling the full lock body

• Clean installation – integrates directly into the door for a low-profile finish

• Compatible with rekeying – can be rekeyed using standard pinning kits and techniques

• Supports commercial security needs – works well within master key and IC core systems

• Durable and long-lasting – built for the high-traffic, heavy-use doors mortise locks are typically installed on

Because mortise cylinders combine strong security with straightforward serviceability, they remain the standard choice for commercial and heavy-duty residential mortise lock hardware.

Related: mortise cylinders · mortise cylinder accessories · rim cylinder · types of locks