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Locks and lock terminology

These are the terms of interest to someone choosing and fitting locks and door and window furniture. They focus on the outside of the lock, etc. rather than the inside.

Rim lock: fits on the face of the door, rather than being set into the body of the door itself

Mortice lock: a lock set into the body of the door, in a prepared hole that woodworkers call a mortice

Latch: a bolt that is sprung ("live") and with a bevel on one face; so the door can be latched shut simply by pulling it to

Nightlatch: a lock that is operated by a key from the outside and a knob from the inside

Deadbolt: a rectangular-section bolt that can only be disengaged with a key or thumb turn; unlike a live latch, a dead bolt is not sprung and cannot be pushed back

Hook bolt: (or claw bolt) necessary for sliding doors; also found on hinged doors where they make it more difficult to force the door and frame apart

Cylinder lock: there are pins, usually 5 or 6 but can be 10 or more, that stop a cylinder from turning; the key lifts the pins

Euro profile: a cylinder lock mechanism utilising a cam actuator. Used in a mortice lock, the lock's cylinder can easily be replaced without replacing the whole lock; inside and outside can both be key-operated or the inside can be provided with a thumb turn

Lever lock: levers (more substantial than pins) stop a bolt retracting; the key lifts the levers

Very often, but not always, a cylinder lock operates a latch rimlock (or night-latch); and a lever lock operates a mortice deadbolt.

Automatic deadbolt: as the door closes, a deadbolt automatically engages

Automatic deadlatch: when the door has closed and latched, the latch cannot be retracted, for example with a credit card

Backset: the distance from the door edge, assuming the lock has been correctly fitted, to the centre of the keyway; a typical rim cylinder lock, for example, comes with either a 40 mm or a 60 mm backset

Strike: the hole or box in the door jamb into which the bolt enters; also known as a keep or keeper

Striking plate: the plate on the strike upon which the latch strikes and operates

Snib: a knob to hold the bolt retracted or deadlock it

Differs: the number of different key patterns for a lock

Wards: these are the the obstructions that give a lever lock keyway a non-rectangular section thus requiring a key with matching section; there can be wards on the back plate of the lock requiring matching cutouts on the leading face of the key; on very old, and on cheap, two-and three-lever locks, this is part of the, limited, protection

Skeleton keys: keys thin enough and flexible enough that they can get past the wards

BS3621: an insurance standard for locks, specifying, for example, the minimum number of differs, that there is protection against drilling and sawing, and that the strike box is metal (equivalent to the European standard EN12209)

E: European—as in the difference between, for example, a Chubb 114 and a Chubb 114E, where the European standard (and now BS3621:2004) asks for a bolt that throws (extends) 20mm, rather than the 14mm throw required by BS3621:1998

Rack bolt: a bolt with teeth along is length, that is operated from the inside only, and is extended and retracted by turning a toothed key

Barrel bolt: the common-or-garden cylindrical shoot bolt that has a knob for hand operation

London bar: because a rim lock isn't set into the door and frame, it's vulnerable to a kick; a London bar fits over the strike box (or staple, or keep) and better secures it to the frame

Birmingham bar: like a London bar, but simply a straight bar to reinforce the frame; attached with non-returning screws if fitted to the outside

Hinge bolts: short bolts that engage the door into the frame on the hinge side as it closes, increasing resistance to forced entry and countering attacks to the hinges if they are visible from outside

Escutcheon: plate fitted around keyholes and handle spindles to hide the holes in the wood, stop the key marking the wood and perhaps to strengthen

Lock reinforcing plate: cutting a mortice into a door in order to fit a mortice lock weakens the door; when a door isn't substantial enough to take this, a reinforcing plate, bolted to the door around the lock area, can compensate and resist kicking attacks

Sash: a puzzlingly overused term: the word is basically just another word for frame;

Sash window: sliding windows, usually vertically, usually in pairs; would be more accurately described as a double-hung window where each window has its own sash

Sash lock: on a window, it locks a sash in place; on a door (and another puzzle), it has come to mean a lock combining a handle-operated latch and a key-operated deadbolt in one mortised lock

There is yet another puzzle here. Why did sash windows become popular in the UK? They seem to have almost no redeeming features compared with, say, casement windows; and are found almost nowhere else.

Casement window: a window where the sash is hinged rather than sliding

Muntin: a strip that separates panes in a sash

Mullion: a vertical separator dividing a window or other opening

Pane: a piece of glass in a window

Light: an opening in a window

Fanlight: a semi-circular pane, usually at the top of a window or a door

Transom: a window above a door, or the horizontal strip between panes in a window, or between window and door


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