Key relevance

[1] It can also refer to the measurable difference between a key and the size required to fit and operate the keyway of its paired lock.

In all machining work, there are measurable amounts of difference between the design specification[2] of an object, and its actual manufactured size.

In locksmithing, the allowable tolerance[3] is decided by the range of minute differences between a key's size and shape in comparison to the size and shape required to turn the tumblers within the lock.

[4] "Key relevance" may also be applied to types of electronic locks when used to refer to similarities in magnetic signatures or radio codes, though truly digital-coded radio signals do not have key relevance ratings because they must have precise unlocking codes, with no degree of difference whatsoever in order to operate.

The term has also occasionally been co-opted by broader mechanical engineering to refer to the similarity of fit between two interlocking machined parts, although "tolerance" or "backlash" has gained far wider adoption and acceptance in usage.

The difference in size between the original key (blue) and its copy (red) is 0.023mm, an accuracy of 0.61%. This is an acceptable level of tolerance.