Keys work by lifting small pins inside a lock to the exact height that frees the cylinder.

The longer version

Inside a pin tumbler lock sits a cylinder that cannot turn while small pins bridge the gap between it and the housing. A spring pushes each pin down, and the blade of the right key lifts it until the split in the pin lines up with that gap. Only when every pin is aligned at once can the cylinder rotate and withdraw the bolt.

The cuts on a key are therefore a code of heights, one per pin, which is why a nearly correct key fails completely: a single pin left too high or too low keeps the cylinder blocked. Picking works by dealing with each pin separately, and the number of possible height combinations is what makes blind guessing impractical.

Where this entry sits

Odd Little Things looks at the ordinary objects people touch every day and the small mechanisms and histories hiding inside them. Buttons, zips, pencils, mirrors, stairs, stamps, packaging, and road signs all get their turn. The full list sits on the Odd Little Things page, where every entry is listed in order.