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Glossary of lock terms

Author: Luku Expert

How to understand different lock-related terms?


Access Control Device

Any device or system that selectively allows entry by certain persons to an area while excluding others. Usually, this term is not used to refer to ordinary key-operated locks but rather to push-button, card access or biometric systems.

This is the feature of a door closer unit that prevents shock and possible damage, when the door is opened forcibly.

The horizontal distance from the face of the mortice lock to the centre line of the cylinder, key hole or knob hub.

Bathroom lock

A mortice lock which is used with thumbturn handles to allow the occupant of the bathroom to lock the door from the inside.



Movable part of a lock or latch that usually engages a component fixed to a frame and is withdrawn into the case.



Installed within the door or frame, mortised and hidden from view.


The lock component where the key is inserted. Also known as a "Cylinder" or a "Keyhole".


A mortice deadlock does not have a latch, but a bolt only which is operated by key.

Some nightlatches have a deadlocked function that adds extra security to the locking mechanism after the key has been rotated for a second time.


Door chain

Also called "Door limiter". A fitment that restricts the door to being partially opened in order to identify callers prior to opening the door for access. Can be either an integral part of the lock mechanism or surface mounted on the inner face of the door.

Door closer

A device which automatically controls the closing or position of a door usually via a hydraulic mechanism.

Door coordinator
In conjunction with a pair of doors, a device designed to cause the inactive leaf to close first.

Door limiter

See “Door chain”.

Door sleeve

A metal sleeve that is put around the lock and strike that reinforces the door and hides cosmetic damage. Also known as a "Door sleeve", "Wrap-around plate", or a "Door wrap".

Door viewer

A viewer drilled into the door that allows one to see outside without needing to open the door. Also known as a "Door viewer", "Peephole", or "Eyehole".

Electric strike
An electrical device that permits releasing of the lock in the door from a remote control.

Electrified lockset

A lock which is controlled electrically.


Surround with a shaped hole, with or without a pivoted cover plate, primarily to protect the door leaf from abrasion damage caused by key insertion. This could be for decorative purposes or to increase the security of the locking device.


Another term for multi-point-locks usually used on windows.

Europrofile cylinder

A cylinder barrel with a specific shape that is compatible with europrofile mortise locks. Europrofile cylinders are available in a variety of types, sizes and finishes.


The exposed surface of a mortice lock which shows in the edge of a door after installation.


The color of the metal of the door hardware.

Flush bolt

A bolt that is mortised into the edge of a door that will lock either or both the top and bottom of the door. Usually used on a pair of doors so that one door will remain closed or inactive, allowing the other door to lock into it.

Grand master key

A key which will operate two or more groups of locks, where each group can be operated by individual master keys and locks within each group can be operated by different keys.



Some styles of levers are handed, usually due to a curved lever design. There are left-handed levers and righthanded levers. To determine the appropriate handing for your door, look at the hinges from the exterior side of the door. As you stand outside facing the door, if the hinges are on the left, you require a left-handed lever. If the hinges are on the right, you need a right-handed lever.

High security lock
Generally any lock that uses patented or unconventional design features to thwart the most common types of attacks on locks - picking, drilling, key duplication, and force. Most high-security locks are especially resistant to vandalism and conventional means of fitting a key. Some, but not all high-security locks also come with restricted keys.


Keys can be used to lock or unlock the lock from inside or outside and/or extend or retract the deadbolt and/or retract the latch.

Keyed alike (KA)

Indicates identical key for two or more locks. The locking action is achieved by a bolt that shoots out of the lock into the striker plate when the key is turned.



A lock with a spring-actuated latch bolt. Nightlatches are still sometimes referred to by their traditional name of “rimlock” although a rimlock usually now refers to a basic security lock for use on internal doors, gates or outbuildings.


A detachable and portable lock with a shackle which locks into its case.


Generally entails disassembling a lock to replace the pins or tumblers inside. Once completed, the lock requires a different key to operate than before.

Rim lock

See “Nightlatch".


The circular plate surrounding the knob or lever that is flush against the door.


A button or slider on a nightlatch that enables the latch to be “held back”, preventing the door from accidentally slamming shut.


The spindle is a square metal bar which connects the door handles on either side of your door together through the follower. When the levers of your door handles are pressed, the spindle rotates and operates the latch inside the door, allowing the door to open.


Striker plate

Flat metal plate appropriate to the lock or latch, fixed to a frame to engage the bolts.


The measurement of the projection of a deadbolt latch.

Thumbturn cylinder

A knob fitted to one end of a cylinder which allows the door to be unlocked without a key from one side only (usually inside).


An electronic device that emits a unique radio signal. When the key is operated in the ignition lock, the on-board computer transmits a radio signal to the key. If the key is properly programmed, it echoes back the correct signal. The computer then allows the engine to start.

Turn knob
Turning mechanism that activates the door lock.




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