How Do Mortise Locks Work?

Written by emily beach
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How Do Mortise Locks Work?
(Creative Commons)

What is a Mortise Lock?

A mortise lock is a hardware device that fits into a pocket within a door. It is considered much more secure than cylindrical or tubular locks, and is the primary type of lock used in commercial applications.

Mortise locks are composed of a number of different parts. There is the lock body itself, which is generally several inches wide. The latch, which is used to lock the door, is contained within this lock body. A strike box is installed in the door frame, and is covered by a strike plate. The strike box catches and holds the latch to keep the door locked. Finally, trim and handles are installed on the outside of the door, and are used to operate the lock.

Mortise Lock Operation

A mortise lock relies on a lever or sliding bolt lock mechanism. To operate the lock, a key must be inserted into the lock cylinder and turned. When the correct key is used, the pins within the cylinder line up and release the latch or bolt. The door can then be opened freely using the knob or lever handle. If the wrong key is used, the pins will not line up, and the cylinder will prevent the latch from releasing. Some mortise locks are designed with a passage function. This means that they do not require a key, and can not be locked. Instead, they can be freely operated at all times by turning the knob or level.

Mortise Lock Cylinders

Many commercial mortise locks come equipped with cylinders, which can be removed or replaced as needed. This allows all the locks to be changed quickly and easily in the event of a security breach. Rather than replacing the entire mortise lock, the cylinder can be removed using a control key, and a new cylinder is installed instead. Some cylinders used on mortise locks allow building owners to simply remove the core of the cylinder (where the pins are housed), rather than the entire cylinder. This is an economical way to quickly and easily re-key the locks.


Mortise lock installation requires a pocket to be created in the door. This is a fairly complex task for most homeowners, and is best left to a locksmith. In commercial applications, most doors are prepped at the factory to accommodate mortise locks, making installation quick and easy.

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