Differs

=Differs=

Differs is an English locksmithing term that refers to the number of possible keys for a given lock. This number is a factor of the design of the key, the number of locking components, the number of available positions 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.

In keyless combination locks, the number of differs may be referred to as permutations, combinations, or sequences.

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.

In rotary combination locks, the size of gates has a dramatic effect on the number of possible permutations. Poor quality locks may have tolerances as low as +/- 3 numbers. In addition, most rotary combination locks have an area of the wheel that cannot be used for the last part of the combination, sometimes referred to as the restricted zone or the danger zone.