Bittings

Bittings are the series of notches cut along the edge of a key blade. Each bitting corresponds to a specific cut depth that, when matched to a lock’s pin or wafer stack, allows the lock to operate. The complete set of bittings on a key is its bitting code, used to reproduce the key and to align the key’s cuts with the internal components of a lock.

In a pin-tumbler lock, the depth of each cut determines how high each pin stack sits when the key is inserted. A correctly cut key positions every pin so that the gap between the top and bottom pins aligns with the shear line, allowing the plug to rotate. If any pin is not properly aligned, the shear line remains blocked and the lock will not turn. The same concept applies to other mechanisms that use edge cuts, though the specific geometry can vary by lock type.

Bittings are typically expressed as a sequence of numbers or letters in a bitting code. The code maps to particular cut depths, and mapping can vary by manufacturer and keyway. Locksmiths use bitting charts or code-cutting machines to reproduce keys from codes, or to create working copies from measurements. In some systems, master keys add extra bittings to enable multiple users to operate the same lock while preserving security.

Variations in bitting conventions arise from different key profiles, lock families, and security levels. Higher-security systems may employ restricted bitting codes, more complex keyways, or additional mechanisms to limit unauthorized duplication.