It’s my understanding that mass produced items are all basically the same. If you buy something like a toothbrush, for example, then any other toothbrush from that same assembly line is going to be basically the same and have all the same specs (with the exception with minor defects here and there), because the machinery and process to make any those toothbrushes are all basically the same.
But that can’t be the case with locks and keys. Because if every lock and key were the same then there’d be no point in having them. Anyone could just bought the same key/lock combo could use it to unlock your front door. So all or most keys and locks must be unique. So how are they mass produced in a way that preserves their uniqueness?
When my wife and i moved into a flat, I noticed the lock was nearly done for. So I exchanged the cylinder with something that was a real quality lock, and gave the landlord a copy of the key in a sealed case.
When we moved out, I informed the landlord that we had exchanged the lock because it was busted, and i would replace the current lock anyway - if they provided a new cylinder i would install it for them. They declined and insisted that I install the original lock. They didn’t test it, and had to get a locksmith…