In terms of thermal expansion, why is it important that a key and its lock be made of the same or ....?

Question

In terms of thermal expansion, why is it important that a key and its lock be made of the same or similar materials?

Answer 1

Probably because when the key and lock are manufactured, they are made to precisely the same shape; that is how they function together. If at some later time, the lock becomes very cold (say by exposure to the elements) while the key stays warm in your pocket, then the lock will shrink slightly while the key will not. They will not work together.

The important part is that if they are the same materials, then the key will quickly cool off and shrink THE SAME AMOUNT that the lock did, and will then work. If it is made from a different material, then the key will shrink a different amount - or if it is a carbon fiber key, it will not shrink at all, so it will never work (until Spring anyway).

The real problem is to make the thermal effects work on both the key and the lock identically, so that they match when you need them to.