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Glossary of Locksmithing Terms
A plain-English A–Z of the locks, parts, keys, standards and techniques a locksmith works with — so when you read a quote or a product description, nothing has to be a mystery.
A
- Access control
- Any system — keypad, fob, card or app — that governs who is allowed to open a door, used most often on commercial premises.
- Anti-bump
- A cylinder design that resists “bumping,” an attack where a specially cut key is tapped to jolt the pins past the shear line.
- Anti-drill
- Hardened steel pins or plates built into a cylinder to blunt or stop a drill bit and frustrate a drilling attack.
- Anti-pick
- Specially shaped pins, such as spool or serrated pins, that catch when a lock is manipulated and make it far harder to pick.
- Anti-snap
- A euro cylinder engineered with sacrificial sections so that, if it is snapped, only the outer part breaks away and the locking mechanism and door stay secure. Look for TS007 3-star or Sold Secure Diamond.
- Astragal
- A moulding fitted to the meeting edge of a pair of doors to cover the central gap and improve the weather and security seal.
B
- Backset
- The horizontal distance from the edge of the door to the centre of the keyhole or spindle; it must match when a lock is replaced.
- Barrel
- A common everyday name for a cylinder, particularly a euro or rim cylinder.
- Bitting
- The pattern of cuts along a key’s blade that lifts each pin to exactly the right height to open the lock.
- Bow
- The shaped head of a key that you grip to turn it, often stamped with the maker’s name or a key code.
- BS10621
- A British Standard for locks that can be key-locked from the outside to override the inside thumbturn, useful for shops secured overnight.
- BS3621
- The kitemarked British Standard for a key-operated deadlock that most home insurers require on final exit doors; it must be locked by key from both inside and out.
- BS8621
- A British Standard for “keyless egress” locks that lock by key from outside but release by a thumbturn inside, used where people must escape without a key, such as flats and HMOs.
- Bump key
- A specially cut key used in the bumping technique to try to force a pin-tumbler lock open.
C
- Cam
- The flat tongue on the back of a cylinder that turns with the key to drive the door’s bolt or mechanism.
- CEN grade
- A European strength rating — BS EN 1303 for cylinders, BS EN 12320 for padlocks — running from 1 to 6, with insurers often specifying a minimum.
- Composite door
- A door built from layered materials such as timber, insulating foam and a GRP skin, usually fitted with a euro cylinder and a multipoint lock.
- Cylinder
- The key-operated core of a lock; the common UK types are the euro cylinder, oval cylinder and rim cylinder.
D
- Deadbolt
- A solid bolt thrown by a key or thumbturn that cannot be pushed back once locked, unlike a spring latch. Also called a deadlock.
- Decoding
- Working out a lock’s key combination, often with a specialist tool, so it can be opened or a key cut without the original.
- Destructive entry
- Gaining entry by damaging the lock or door, such as drilling the cylinder, when non-destructive methods are not possible.
- Differs
- The number of unique key combinations a lock design offers; more differs means less chance that another key will accidentally fit.
- Dimple key
- A key cut with conical dimples across its flat faces rather than a serrated edge, used with higher-security dimple cylinders.
- Driver pins
- The upper, spring-loaded pins in a pin-tumbler lock that block the plug from turning until the correct key lifts them to the shear line.
E
- Escutcheon
- The plate or cover around a keyhole or cylinder on the face of a door, which is both decorative and protective.
- Espagnolette
- The long internal rod-and-gear system in many windows and French doors that throws bolts at several points from a single turn of the handle.
- Euro cylinder
- The most common UK cylinder, a standardised profile used in uPVC, composite, aluminium and many timber doors; upgrade to an anti-snap (TS007 3-star) version for security.
F
- Faceplate
- The flat metal strip along the edge of a mortice lock or multipoint mechanism, visible on the edge of the door. Also called the forend.
- Five-lever mortice lock
- A lever lock with five levers; a version certified to BS3621 is the insurance standard for timber doors.
- Follower
- The square hub inside a lock that the spindle passes through, transferring the handle’s movement to the latch.
G
- Gearbox
- The central mechanism of a multipoint lock that converts the handle lift and key turn into the throwing of the hooks and bolts; it is the part that most often fails.
H
- Handing
- Which way a door is hung and opens — left or right, inward or outward; many locks and handles are handed to suit.
- Hinge bolts
- Fixed steel pins on the hinge edge of a door that locate into the frame so the door cannot be levered off its hinges.
- Hook bolt
- A hooked bolt, found on patio and multipoint locks, that swings out and grips the keep to resist the door being slid or forced apart.
J
- Jamb
- The vertical side member of a door frame.
K
- Keep
- The metal plate or box recessed into the frame that the bolt or latch shoots into. Also called a box keep or strike.
- Key blank
- An uncut key of the correct profile, ready to be cut to match a particular lock.
- Keyed-alike
- A set of locks arranged to open with the same single key, convenient where one key should fit several doors.
- Keyed-to-differ
- Locks that each have their own unique key, the opposite of keyed-alike.
- Keyway
- The shaped slot in the cylinder plug that will only accept keys of the matching profile.
- Kitemark
- The BSI Kitemark, a certification symbol showing that a product has been independently tested and meets a British Standard.
L
- Latch
- A spring-loaded, bevelled bolt that holds a closed door shut but can be pushed back; on its own it does not lock the door.
- Lever lock
- A lock operated by a mortice key lifting a stack of levers to the correct heights, common on timber doors and usually 3-lever or 5-lever.
- Lock snapping
- A common attack on cheap euro cylinders in which the cylinder is gripped and snapped in two to expose the cam; anti-snap cylinders are designed to defeat it.
M
- Master key
- A key that opens every lock within a planned suite, while each lock still has its own everyday key.
- Master suite
- A planned set of locks whose keys are arranged in a hierarchy, so a master opens everything and sub-masters open defined groups.
- MLA
- The Master Locksmiths Association, the UK’s recognised trade body, whose approved companies are vetted and regularly inspected.
- Mortice
- A pocket cut into the edge of a door to house a mortice lock or latch, which sits inside the door rather than on its surface.
- Mortice lock
- A lock fitted into a mortice in the door edge; a sashlock has both a latch and a deadbolt, while a deadlock has a deadbolt only.
- Multipoint lock
- A locking system, standard on uPVC and composite doors, that secures the door at several points — hooks, bolts and rollers — when the handle is lifted and the key turned.
N
- Night latch
- A rim latch, the classic “Yale” type, that locks automatically when the door closes and is opened by key outside and by knob or lever inside.
- Non-destructive entry
- Opening a lock without damaging it or the door, using picking, decoding or specialist tools; it is a hallmark of a skilled locksmith.
O
- Oval cylinder
- A cylinder with an oval profile, used in some mortice deadlocks and commercial hardware rather than the euro profile.
P
- Padlock
- A detachable lock with a shackle, graded by Sold Secure and BS EN 12320 for securing sheds, gates, stores and outbuildings.
- PAS 24
- An enhanced security performance standard that a complete doorset or window can be tested against, often required under Building Regulations or Secured by Design.
- Pin tumbler
- The most common cylinder mechanism, using pairs of spring-loaded pins that must all align at the shear line before the plug can turn.
- Plug
- The rotating inner core of a cylinder, into which the key is inserted and which turns to operate the lock.
R
- Raking
- A quick picking method that scrubs a tool across all the pins at once hoping to set them, as opposed to careful single-pin picking.
- Restricted key
- A key whose blanks are legally protected so copies can only be cut with the owner’s authorisation, preventing unauthorised duplication. Also called a patented key.
- Rim cylinder
- A cylinder that passes through the door to operate a surface-mounted rim night latch or rim lock.
- Roller bolt
- A spring-loaded roller used in place of a latch, common on French and double doors so they hold shut without a sharp latch.
S
- Sashlock
- A mortice lock that combines a latch, worked by the handle, and a deadbolt, worked by the key, in a single case.
- Secured by Design
- The official UK police security accreditation for products and buildings that meet recognised crime-prevention standards.
- Shear line
- The gap between a cylinder’s plug and its housing; when every pin aligns at this line the plug is free to turn and the lock opens.
- Shootbolt
- A bolt that shoots up or down into the frame, used on French doors, patio doors and multipoint locks to secure the top and bottom.
- Snib
- A small catch or button that holds a latch open or locked without a key, a term used mainly in Scotland and the North.
- Sold Secure
- A respected UK testing scheme — Bronze, Silver, Gold and Diamond — that rates products against real attack methods, with insurers often specifying a minimum.
- Spindle
- The square bar that passes through the door and the lock follower to connect the handles on each side.
- Spool pin
- A security driver pin shaped to catch during picking, creating a “false set” that makes the lock much harder to manipulate.
- Strike plate
- The metal plate on the frame that the latch or bolt strikes and locates into; see also the keep.
T
- Thumbturn
- A small twist knob on the inside of a lock that locks or unlocks it without a key, allowing keyless escape.
- TS007
- A UK kitemark scheme that star-rates euro cylinders and door handles for snap resistance; a 3-star result — a 3-star cylinder, or a 1-star cylinder with a 2-star handle — is the recognised anti-snap benchmark.
U
- uPVC door
- A plastic-framed door, almost always fitted with a euro cylinder and a multipoint locking mechanism.
W
- Ward
- An obstruction inside a keyway or lock that blocks all but the correctly shaped key. The shaping itself is called warding.
Y
- Yale lock
- A common everyday name for a rim night latch, after the well-known manufacturer.
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