Quora specializes in personal experience stories from insiders of all sorts. Nice example just now.
Question: How do lock manufacturers insure that all keys are different?
Answer: They can’t.
I already knew this part, just from estimating the math. There are about 10 variable points on a key. If you have 3 different heights available for each point, you have about 60k possible keys. Nowhere near the number of locks in the world, even if you allow for the various dimensions and main shapes of key.
Insider part that I couldn’t guess: It’s far more important to insure that SOME locks are the SAME. A car fleet like a police force uses the same key for all of its ignitions, so any cop can jump into any car without fiddling with dozens of keys. (Key 54, where are you?)
In the 90s when cops everywhere used Ford Crown Vics, all of the cop Vics everywhere had the same key. When cops from different cities were working together, any cop could drive any of the cars.
Polistra's Mill 