The bitting of a key is the physical arrangement of the bits of the key that engage with the locking mechanism. The bitting instructs a locksmith how to cut a certain key, to replace a lost key or make an additional copy.
In lever tumbler locks, a bolt stump is a rectangular part located above the talon, and passes through the slot in the levers as the bolt moves.
A break in the pins is a separation in one or more sections of the pin used to encode the lock for a specific key or set of keys in a master keying system.
A dual custody locking system is one where two different keys, generally given to different people, are required to open the lock. These are often used in safe deposit boxes.
A metal plate on the lockset itself (on the door, not the jamb) is called a face plate.
A glass relocking device is a piece of glass, usually tempered, placed where it might be expected to break in a burglary attack. It is attached, usually with wires, to one or more spring-loaded bolts, which are often randomly located. A drill or torch may break the glass, releasing the bolts.
The lock housing, also known as the bible, refers to the part of the lock that does not move when the lock is opened. The driver pins of a pin-tumbler lock are located in the bible.
The plug is the part of a cylinder lock which is designed to turn when a key is inserted.
A plug follower is a device used in the assembly and disassembly of locks; it is a solid cylinder that is used to push the plug out of the lock, while preventing the springs and driver pins from moving.
A relocking device (RLD) (a.k.a. "external relocker") is an auxiliary locking device intended to be activated during an attempted burglary of a safe or vault. Such a device will keep a safe or vault locked even if the primary lock is defeated. This independent mechanism is designed to maintain the locked state of a safe even if the lock itself is destroyed. This auxiliary locking device usually consists of a spring-loaded bolt of some type, held in check by a bracket or cable that is rigged to release the mechanism in a burglary attempt. The device will either block the main boltwork from retracting or block the door from opening. Glass relockers are one of the most common types of relockers used in today's safes.
Relockers are typically designed for one-time activation, meaning that once they are triggered the device is locked "permanently" and can only be opened by brute force.
A security pin is a pin designed in a non-standard way to attempt to prevent the lock from being picked. Examples of security pins include serrated pins, spools, and mushroom pins.
In a cylinder lock, the shear line (also known as the split line in Australia), is where the inner cylinder ends and the outer cylinder begins. When a break in the pin is reached by picking, the pin will "hang" at the shearline due to the space between the inner and outer cylinder. This "imperfection" in the lock mechanism is an unavoidable defect in the manufacturing process that allows for lock picking.
A snib is a device to engage or disengage a lock without the use of a key. In Scottish English or Irish English, the word is sometimes used as a synonym for lock.
A strike plate is a metal plate affixed to a doorjamb with a hole or holes for the bolt of the door. When the door is closed, the bolt extends into the hole in the strike plate and holds the door closed. The strike plate protects the jamb against friction from the bolt and increases security in the case of a jamb made of a softer material (such as wood) than the strike plate.
Some strike plates have their hole size and placement calculated so a spring-bolt extends into the hole, but an adjacent anti-retraction device remains depressed, preventing the bolt from being retracted unless the lock is turned.
Thermal relocking device
Designed as a defense against torch attacks, these are simply relocking devices equipped with a fusible link designed to melt and release the relocking device if the temperature inside the door exceeds a certain temperature (usually 65 °C), as would happen in a torch attack.
^Mick Friend (2004), The Encyclopaedia for Locksmiths, Authors OnLine, Ltd., p. 34, ISBN0-7552-0117-5