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Glossary of Lock Terms

Useful list of common locking terms and abbreviations.

Automatic Deadlocking

A device fitted to a lock or latch which reverts to a deadlock state when the door is closed.


The horizontal distance from the edge of a door to the centre of the keyhole or follower.


A bar, securing a door to its frame or the floor

Case Size

The distance from the forend to the back of the lock case



An unsprung bolt, usually rectangular in shape, which is locked and unlocked with key only.  The exception to this are bathroom and Escape locks where the deadbolt can be operated by a turn or a knob from the inside only.  On better quality locks and security locks, the deadbolt will be reinforced with hardened steel rollers to deter attack by sawing.


A simply lock, operated by a key which when turned deadlocks the door.  It cannot be opened without the key.  A Deadlock does not have a handle or latch.


An alternative form of locking lever which offers a greater number of key combinations, particularly when locks are master keyed


The number of different key combinations that are obtainable from a particular lock mechanism.

Disc Tumbler Mechanism

A Mechanism which for security employs spring loaded flat plates in a plug locating into slots in a surrounding barrel.  Used extensively on motor vehicles and office equipment.

Door Furniture

Fittings mounted onto the surface of a door.  Usually both functional and decorative e.g. knobs, lever handles, letter plates, pull handles etc.

Door Chain

Allows the door to be part-opened to see who is there.

Door Stile

The vertical outer section of a glazed panelled door which may determine the maximum backset or case size of the lock to be fitted.

Door Viewer

A door viewer or spy hole is used for seeing who is at the door without actually opening it.  They are particularly useful for the elderly and are easy to fit.

Dual screws

Suitable for most sash and sliding windows.


Plates which are used when a deadlock is fitted to cover any irregularities of the wood around the keyhole.  Some escutcheon have a cover which helps to prevent drafts and ensures privacy when fitted to the internal face of the door.

Face Plate Trim plate or outer forend which is the only part of a fitted mortice lock that is visible.
Follower The square visible on the outside of a lock.  It is turned by the spindle of a knob or lever handle and operates the spring or latch bolt.
Forend The part of the lock or latch through which the bolt(s) protrude, and by which the lock or latch is fixed to the door.
Handling Locks and some door handle are handed either left-hand or right-hand, dependant upon a number of varying conditions which are apparent on the door to which they are being fitted.  Most locks with bevel shaped Latch Bolts can be easily reversed to suit there application, locks with roller bolts can be used either without the need to make any modifications.
Hasp The hinged part of a hasp and staple.
Key A device to throw or withdraw the bolt of a lock.
Key Plate
See Escutcheon.
A device for keeping a door closed.  It has no key and offers no security.
latch Bolt A spring loaded bolt, bevelled on its striking face which operates automatically when the door is closed.  Withdrawn by the knob, handle or key.  Also know as a spring bolt.
Lever A moving obstruction in a lock activated by the key.  Use of the wrong key will either overlift or underlift the lever rendering the lock inoperable.  The grater the number of levers, usually the better the security.
Master Keying
An arrangement which allows one key to operate over a number of differing locks.  It is widely held belief that master keying increases security, on the contrary, it reduces it, both mechanically and by the fact that every lock within a suite has two keys.
Obstructions placed within a lock to prevent the wrong key operating it.  There are two types, (1) moving obstruction, such as levels, tumblers, detainers and pin tumblers, and (2) fixed obstructions such as wards and bullets.


A slot or hole cut into the edge of a door into which a lock or latch is fitted.

Mushroom Head Rollers
Anti-pick device, incorporated into the pin tumbler mechanisms.
Nightlatch A latch employing a spring bolt operated from the outside by the key and from the inside by knob.  Usually employing a thumb turn or snib to hold the bolt in the withdrawn position.  Most nightlatches have the supplementary devices to improve their security.  Available as rim or mortice patterns.
Pin Tumbler Mechanisms
A plug is secured to its sleeve or barrel by several spring loaded pins which protrude into it.  When the correct key is inserted, the pins are withdrawn until they are flush with the plug and thus allowing it to turn.  Over the years many refinements have been made to improve the security of this type of mechanism.
Rebate The rectangular step shaped recess cut down the leading edge of door, or the edge of a pair of meeting doors.
Rebated Mortice Lock
A lock, whose front-end is stepped to match the recess in the leading edge of the rebated door.  Loose components are mainly used, which when fitted to a flat forend lock, immediately turn it to either a left hand or right hand rebate
Rim Fitting
A Rim fitting is one which is fixed to the external surface of a door.  Patterns include locks, latches, nightlatches, deadlocks, exit hardware, and door closers.
Roller Bolt
A spring bolt which instead of having a bevelled face, has a roller.  Generally, they are quieter with the advantage of requiring no adjustment to suit the handing of the door
A circular, bevelled ring encircling a cylinder.  It has three functions, (1) it is decorative, (2) it locates the cylinder in position on the door and (3) it resists the use of a wrench to grip and twist the cylinder.
Sash Lock
A deadlock with the addition of a handle mechanism and a latch, the lock can be deadlocked with the use of a key.
Security Bolt
A bolt fitted into a door or window which can be opened from one side only, (usually inside) with a splined key “ a key with grooves in it.  Security bolts are usually fitted as additional security to the top and bottom of a door.
The U shaped locking component on a padlock.  On the better quality padlocks, this will be hardened to help prevent sawing.
Snap Lock
Security option for PVCu, wooden casement, transom and pivot windows.  It automatically snaps locked when the window is closed.
A small catch or button on a lock, to hold the bolt either in the withdrawn or in the locked position.
See Latch Bolt
Staple The box, screwed onto a door frame to accept the bolt or bolts of a rim lock or latch.  Alternatively the term is used to describe the fixed part of a padlock.
Steel Inserts
Hardened steel implants set into the bolt of a lock to help prevent assault by hacksaw.  These inserts can be loose fitting to roll under the friction from a saw blade or provide protection against drill attack.
Stricking Plate Metal plates let into and screwed to a door jamb.  Generally used with mortice locks, deadlocks, latches and occasionally with rim locks and nightlatches which have reversed bolts when they are fitted to doors opening outwards.  Some striking plates have a box which helps to prevent the bolts from being attacked with a jemmy.
The distance a bolt travels from the unlocked to the locked position.  Some locks may have the bolt double thrown by an extra turn of the key.
To Pass
A number of locks, from two upwards, which may be operated by the same key.  A popular version of this is with private housing where the front door, the back door and garage door locks are all operated by the same key.


Movable obstructions in a lock which need to be lifted before the key can operate the bolt.

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