Key Differs

When a company advertises their padlocks as having 10,000 key "differs" or key "changes," what are they really talking about?

In a standard pin/tumbler design padlock, which most are, there are a set number of varying length, spring-loaded pin sets--usually 4 or 5--arranged in a row in the tumbler's keyway. When the key is inserted, the "cuts" in the key, push each pin upward a corresponding distance to its length to align along the edge of the tumbler, called the shear line. This allows the tumbler to turn and open the lock.

Key differs are the number of unique pin length combinations (and corresponding key cuts) for a given lock design. And it's simple math. The number of pins raised to the power of the number of pin lengths. So, the possibile combinations for a standard 5-pin lock with 5 different pin lengths is 5x5x5x5x5 = 3125.

However, they're not all usable or truly unique. Due to a variety of factors including manufacturing tolerances, only about 1/3 of the combinations are. Which means that a standard 5-pin lock only has about 1050 truly unique key differs.

So when you see an add for a 5-pin lock with 30,000 combinations, be suspicious. Even if it were mathematically possible, standard manufacturing technology simply can't produce that many unique combinations.