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?
Each tumbler has 4 to 6 sizes in 3 to 6 holes. They set the combination, then cut the key and put the matching tumblers in a standard housing.
Half the security on most locks is that it’s hard to get tools in the tiny slots. The actual number of combinations is small, but difficult to scan through.