Differs

=Differs=

Differs is an English locksmithing term that refers to the number of possible keys or combinations for a given lock. This number is a factor of the design of the key, the number of locking components, the number of available depths for each component, and the tolerances of the lock. Tryout keys are a lockpicking tool used to exploit a low differ count in certain locks.

Real vs. Theoretical Differs
Differs are divided between theoretical and real. Theoretically, most locks have a very high number of differs, but in reality tolerance and bitting restrictions lower this number dramatically. For example, a 5 pin lock with 10 depth spacings has 10^5 (100,000) theoretical key differs. Various key or lock requirements may lower this number dramatically:


 * Cut depths cannot be repeated more than twice in a row.
 * Cut depths changes cannot be greater than a certain number. This is usually done to prevent back-cutting during key removal.
 * Cut depths cannot follow predictable or easy to pick patterns, such as a staircase.
 * Tolerances of the lock allow for fractional depths to correctly set components.
 * Certain types of master keying may restrict various cut depths in non-master keys.