020 8819 1457
South West London despatch point: 10 Cranbourne Close, Norbury, London, SW16 4NG

Locksmith Jargon Buster

Added by: SMR London Local Locksmiths, on: 12th June 2014

Anti-thrust bolt

A spring bolt, for a night latch particularly, which cannot be pushed back when it has shot out and fastened a door, although it can be withdrawn by knob or key. This security device is usually achieved by a dog inside the latch case which falls behind the bolt and keeps it shot out when an auxiliary slide is pushed in.

Anti-thrust plate

An overlapping metal plate fitted to outward opening doors so as to prevent access to lock bolts.

Automatic deadlatch

A deadlatch, the main bolt of which is automatically locked (or deadlocked) when the door is closed.


The plate, fixed on a door, to which the moving parts of a lock or latch are attached.


The horizontal distance from the outside face of the outer forend to the centre of the keyhole or follower hole (or both). Designated as the “keyhole backset” or “follower backset”.

Barrel Bolt

The common kind of door bolt having a round shoot running in a long continuous guide or strap attached by the backplate, the shoot being provided with a knob or the equivalent for operation by hand.

Birmingham Bar

A steel bar fitted to the inside face of a door frame on the hinge side.

Blank (key) or key blank

A partly made key, which has been shaped to enter the keyhole of a certain type of lock or latch, but of which the blade has not been finally notched to operate any individual lock.


The part of a lock or latch which provides the fastening or engagement by protruding from the case or forend to engage in the staple, striking plate, link, shackle or other member.

Bow (of key)

That part of the key which is held in the fingers when operating the lock or latch.

BS - British Standard

Specification Authorised and issued by the British Standards Institute, the accepted UK authority for all standards of performance, tests and manufacture.

BS 3621

The British Standard specification for Thief Resistant Locks for hinged doors. Locks submitted for certification must satisfy the requirements of the ten stringent clauses of the specification .

Burglar Bars

Steel bars, usually round or square in profile, cut to length and fixed internally to window frames.

Cabinet lock

A generic term to include all locks of any type for use on pieces of furniture, such as cupboards, drawers, chests, boxes and the like.


Usually a tongue fixed to the end of the plug of a cylinder lock or latch.

Cam lock

A complete locking assembly in the form of a cylinder whose cam is the actual locking bolt.

Cap (of the lock)

The removable cover to a lock mechanism.

Casement Door

A hinged door or pair of doors almost wholly glazed; often called a French Window.

Casement Window

A window in which one or more lights are hinged to open.


The vertical measurement in an upright or sash lock between the centre of the keyhole and the centre of the follower hole.


A ring with open ends which can be sprung into place on a plug or other part to permit rotation but to prevent endways movement.

Closed shackle padlock

A padlock, the body of which is built up so that the minimum amount of shackle is visible when locked. It offers improved security against forcing or use of bolt-croppers.

Combination Lock

An abbreviation of name for a keyless combination lock.

Cut cabinet lock

A cupboard or drawer lock, the flange of which is recessed into the edge of the drawer or door.


Usually the cylinder with inner co-axial plug which houses the pins, top pins (drivers), or disc tumblers and springs in the cylinder body.

Cylinder housing

With all component parts removed, this forms the main body or housing of a cylinder.

Cylinder key

A key, having a bow and long blade in which “V” cuts are made along the upper edge to operate the pins and drivers in a pin tumbler mechanism.

Cylinder lock or latch

Any lock or latch, the mechanism of which is contained in a cylinder.

Cylinder rose (or ring)

A shaped metal disc which surrounds the outer face of the cylinder of a cylinder mechanism assembly. It usually stands slightly proud of the outside face of door.


The square-ended bolt of a lock which is moved in both the locking and unlocking directions by the key (but occasionally by thumb turn inside only) to provide fastening.
N.B. For obvious reasons, it is inadvisable to incorporate the thumb turn with the deadbolt of any deadlock or lock which is supposed to offer good security, if used on glass or wood paneled doors.


A nightlatch or latch, the springbolt of which can be locked (or deadlocked) by key or other means.


A lock having only a square-ended deadbolt operable from one or both sides by key, and occasionally from outside only by key, inside by thumb turn. Sometimes operable only from outside and with no inside keyhole, which is designated a single-entry deadlock.


1. A generic term, not widely used, for any part such as a lever or tumbler which keeps a lock bolt in position
2. The name of the sliding security members in Butter’s System locks. Differs An abbreviation of “different combinations” or changes.

Disc tumblers

The small shaped discs (usually of metal) in the disc tumbler mechanism which are the means of providing different combinations.

Disc tumbler lock

A cylinder lock having disc instead of pin tumblers.

Door Closer

A device for closing a door or gate automatically after opening. There are numerous types available.

Door viewer

Optical device fitted through a door to enable observation without opening the door.

Double Bitted Key

One with a bit on each side of the shank.

Double-handed lock

1. A lock designed for use either as a right or left hand installation without alteration, generally by turning upside down. The keyhole has a circular formation at each end of the slot to accept the shank of the key.

2. A cupboard lock, the bolt of which can be shot either way to protrude from either side of the case.

Double locking

1. By introducing a different cam arrangement into the action of a cylinder rim nightlatch it is possible to give a double or deadlocking facility at no extra cost. A simple opposite turn of the key in the outside cylinder deadlocks both bolt and inside knob simultaneously. This gives protection against the bolt-forcing and the glass or wood panel breaking intruder.

2. Also where a lever lock shoots its bolt by more than one turn of the key, thus doubling the distance of its shoot.


The cover for the keyhole of a mortice or similar lock.

Face plate

The outer of a double forend. A strip of metal fixed to the inner forend, thus forming a double forend.

Final exit door

The exit door through which entry must later be obtained, and so cannot be bolted. It is usually the front entrance door or final means of exiting.

Flush Bolt

A door bolt which can be recessed flush into the edge or face of a door.


That part of the lock or latch through which the bolt(s) protrude, and by which the lock or latch is fixed to the door.


The additional items needed, which are screwed to one or both sides of the door to enable a lock or latch to be manually operated. Known as door furniture, lock or latch furniture, locksets or latchsets (when complete with lock or latch) and can be either knob, lever handle, pull handle or push button.

Hasp and staple

A fastening in two pieces for a door or box to be secured by a padlock. The hinged part is called the hasp which is fitted to the door or lid of a box and shuts over the staple, which is on the door frame (or other leaf of a pair of doors) or the body of the box. For real security it is essential to use a hasp and staple with concealed fixing,
i.e. the heads of the fixing screws are completely covered when the padlock is locked in position, as otherwise the fitment can easily be removed by withdrawing the screws affording nil security.

Hinge Bolts

Fixed steel protrusions fitted into the rear edge or hinge side of doors, closing into holes cut into the door frame, to protect from forced attack on the hinge side of the door.

Hook bolt

A pivoted springbolt, the head of which is shaped in the form of a hook. Such locks or latches are usually fixed on sliding doors.


The vertical member of a door or window frame. In some areas the top rail of a door frame is referred to as the top jamb.


A small removable device for operating the mechanism of its own lock, locking latch or nightlatch.

Key blank

A partly-made key, which has been shaped to enter the keyhole of a certain type of lock or latch, but of which the blade has not been finally shaped (i.e. notched or bitted) to operate the mechanism of the lock.

Master Key

A key which will open every lock in a master keyed suite.

Master Keyed (locks or latches)

A lock or latch capable of being operated also by a master key as well as its own change or servant key.


A hole cut into the thickness of one edge of a door to receive a mortice lock or latch.

Mortice Key

A key to operate a lever lock, consisting of a bow, shank and bit.

Mortice lock (or latch)

A lock or latch which is morticed or let into the thickness of the door from the meeting edge and held in position by screws through the forend.


A rim or mortice latch with a bevelled springbolt or roller bolt which shoots when the door is closed, but can be withdrawn by key from outside and by knob or lever handle from inside. Usually provided with a stop knob, slide or snib to hold the bolt retracted and to deadlock the bolt when shot in the closed position, even against the
action of the key.

One-sided lock (single-entry)

A lock which has a keyhole on one side only, so that it can be operated by key from one side only, usually outside, but not from both. Nearly all cabinet locks and all padlocks are examples. Some high quality cylinder mortice locks
are one-sided.

One-way action

An action where the follower will turn only one way.


A comparatively small removable and portable locking device, usually but not always key operated on one side only. The locking member is a circular hinged sliding or swivelled shackle which passes through a hole in a staple, locking bar or similar member.

Panel grilles

Steel grilles made to size with various infills of expanded diamond mesh, square weldmesh or fancy infills, usually fitted internally.

Pin tumbler mechanism

The mechanism incorporated in the cylinder or body of a cylinder pin tumbler lock, latch or padlock, usually referred to as a cylinder lock, latch or padlock. Other than padlocks, the cylinder with its co-axial plug housing the pins and drivers under spring pressure passes through the thickness of the door, and the correct key lines up the pins and drivers to make a clear line of intersection between plug and cylinder, thus allowing the plug to rotate and the lock to be operated. The mechanism offers high security against key interchangeability and anti-pick mushroom drivers are usually included in every cylinder. For example, Yale 5 pin cylinders offer up to 24,000 differs as standard. It is also very suitable for master keying, as many different types of locks or latches can be included in the suite. Under master key, 12,200 differs are obtainable and under grand master key, 36 different sub suites with up to a total of 2,200 differs can be provided.


The part of the pin-tumbler cylinder mechanism or disc tumbler cylinder mechanism into which the key enters and which the key turns. It houses the pins of a pin tumbler cylinder mechanism or the discs and springs of a disc tumbler cylinder mechanism.

Rack Bolt

A bolt, usually a door bolt, which is toothed so that it may be operated by a pinion.


The measurement of the stepped reduction or recess in the forend of a rebated lock.

Rebated (lock or latch)

A mortice lock or latch with a forend specially shaped to correspond with the shaped meeting edge of the door for which it is intended. See “Full Rebated”.


A striker in various forms to replace the lock strike and is operated electronically.

Rigid grilles

Heavy duty, welded construction, rod or bar grilles, usually fitted externally or internally to the fabric of a building.

Rim Cylinder

This relates to a pack which usually comprises the cylinder with plug, rose, connecting bar, two connecting screws and two keys.

Rim lock or latch

A lock or latch that is fitted by screwing on to the inside face of the door.


1. A cylinder rose or ring in cylinder locks or latches. It is a shaped metal disc
which surrounds the outer face of the cylinder
2. In door furniture, it is the small plate to which the lever handle or knob is affixed and
which is screwed to the door surface.

Safe Lock

A general term for the many varieties of key operated and other locks for

Sash lock

An upright mortice lock, consisting of a latch bolt and a key operated bolt.
Sash ward Used in rim and mortice locks, alone or in conjunction with levers for the
purpose of obtaining or increasing the differs. Formed pieces of concentric metal are
affixed around the inside of the keyhole. It also serves as a keyhole bush. The bitted key
passes over these wards to operate the bolt. Little security is given when sash wards are
used by themselves. See “Skeleton Keys”.


The hinged, sliding or swivelling loop shaped member of a padlock. The heel of
the shackle remains always in the padlock body and the toe of the shackle comes out
when unlocked. A double locking padlock gives the greatest security against forcing
because there are two separate bolts locking outwards in opposite directions, one into a
niche in the heel of the shackle, and the other into the toe of the shackle. This is
sometimes called heel and toe locking.

Shear Line

The term is used to denote the line of the circumference of the plug in the
bore of a pin tumbler cylinder.


1. The outward movement of a lock bolt and the distance which it travels under
the action of a spring or key. Shoot applies more particularly to spring bolts, throw being
a better word for dead bolts.
2. The sliding part of a door bolt.

Shoot (of bolt)

The distance a springbolt moves under the action of its spring.

Side Bar

This is in addition to the existing pin or disc mechanism, and is a bar usually
along the length of the mechanism and does not allow rotation until the mechanism is
correctly lifted and can be directly controlled by the key.

Side Wards

Notches cut into the sides of bitted keys so fashioned to enable the key to

Sliding grilles

Steel sliding grille gates in single or double leaf, running on top and
bottom guide tracks, locked by padlock or integral lock.

Sliding Lever

A lever which slides between or on guides instead of swinging on a pivot..


That part of the door furniture usually of square section which passes through
the follower hole and is fitted to the knob(s) or lever handle(s) to operate the springbolt.

Spring shackle padlock

A padlock, the shackle of which springs open when unlocked, and is locked by snapping to.

Springbolt Sometimes called the latchbolt.

A bolt having the outer edge shaped by bevelling of the vertical face. It is a bolt which may be pushed back into the lock-case and will return to the extended position without mechanical assistance.


1. A box-like fitting on the jamb of an inward opening door, and into which the
bolt or bolts of a rim latch or lock shoot when door is closed. (It is sometimes referred to
in Scotland and the North of England as a Bosshead). Some staples are lipped to act as
a guide for the springbolt.
2. Part of a hasp and staple for use with a padlock. The padlock shackle passes through
the eye or hole in the staple.

Stop knob (snib)

A device incorporated in some latches and locking latches to hold the
bolt retracted or deadlock the bolt when door is closed.

Striking plate

Sometimes referred to as a “striker”. It is a shaped flat metal plate fixed to
the door frame or jamb with one or more bolt holes into which the bolt or bolts shoot.
There is a shaped projecting lip on one side to guide the springbolt. It is used with all
mortice locks or latches, and with rim locks or latches with reversed springbolt on an
outward opening door.

Suite (of locks)

A group or collection of locks and/or locking latches and padlocks of
different types and changes incorporated together under a master key or grand master

Thumb turn

A small fitting, on the inside of a mortice lock, which is gripped between
thumb and finger to operate the deadbolt. It should not be used on glass- or
wood-panelled doors.

Tie bars

The horizontal members of a vertical bar grille.

Time Lock

A clockwork or electric timing device which disallows operation of a lock or
the opening of a door on safes or strongrooms.


Fixed obstructions inside a lock case to preclude the use of wrong key, as the key is cut to pass over the wards and operate the lock. They are sometimes used in
lever locks to give increased differs. Wards alone give very little security. See “Skeleton Key”.

Warded lock

Any lock or padlock, the mechanism of which makes use only of wards. Not recommended, due to lack of security.

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