The following Glossary of Locksmith Terminology is provided courtesy of the Master Locksmith Association (MLA). Click on a letter below to be taken to its corresponding terms.

Deadbolt - 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 panelled doors.



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

Deadlock - 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.

Detainer - 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.

Divided Follower - Another name for a split follower, to allow independent operation form either side of a lock case.

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 Feather Spring - Two separate feather springs, fitting closely together one inside the other. Alternatively both may be made from one length of material and remain joined at one end. A spring so made is more lively and likely to last longer than a single spring of thicker material.



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.

Drilled-through spindle (for lock furniture) - Usually shortened to DY A spindle with a few holes drilled at each end, one of which accepts the screw passing through the neck of the knob (or lever handle) in the door furniture.

Drillpin (sometimes pin) - A fixed stump or pin in a lock onto which the hollow shank of a pipe key fits when inserted to operate the lock.

Drivers (Top pins) - Pins that rest outside the plug of a cylinder when the key has created the shear line and are housed in the chambers of the cylinder housing. Drivers can be of various shapes other than cylindrical, so as to form anti-rap pins or anti-pick pins. See “Mushroom Drivers”.

Drop - 1. In drawer, chest, box or similar cabinet locks, the vertical distance from the outside face of the top edge or selvage to the centre of the keyhole.
2. Sometimes this term is used for a keyhole cover on a padlock.

Drop Arm - The member C in the illustration below, by which the bolt of the keyless combination lock is operated when the combination is set up.



Dust cap (or cover) - A keyhole cover on a padlock and some car-door locks to prevent dust from entering the keyway. It is actually an escutcheon.

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