How come Key A can open Lock A. Key B can open Lock B. But not lock A. And key C can open all the locks? Doesn’t that mean A and B should be able to open each other?
In: 731
Locks have pins in them that when aligned properly, the lock can turn. In each slot, there’s a driver pin and a key pin. Each one will a different length, determining how the key has to be cut to open the lock. When the gaps between the pins are all aligned with each other and the edge of the part of the lock that turns, called the shear line. When all of that lines up, the lock can turn.
[Visual explanation](https://thumbs.gfycat.com/AcceptableAccomplishedAfricangoldencat-mobile.mp4)
If you want a master for those lock, in-between the driver and key pins (in at least one slot) you add what’s called a master wafer. This adds another break between the pins, meaning there’s a different combination distances to push the pins that also opens the lock. To have several different locks that all open to the same master, ideally you would have all the pins but one be the same, and then the last pin has a different sized master wafer in each lock such that the master key fits all of the locks.
For example I’ll use arbitrary numbers for pin lengths:
1, 2, 3, 4
1, 2, 3, 5
1, 2, 3, 6
Each one needs a unique key, but if we give each one a master wafer in the last spot of lengths 3, 2, 1 respectively
1, 2, 3, 4/7
1, 2, 3, 5/7
1, 2, 3, 6/7
Each one’s unique key still works, but a key for 1, 2, 3, 7 will fit all 3 locks
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