Padlocks keep a shackle locked until the correct key or combination releases the internal catch.

The longer version

A padlock holds its shackle with a catch inside the body. In a keyed lock, the same pin principle as a door cylinder blocks rotation until the right key lifts every pin; in a combination lock, a set of discs must be turned so their notches line up and let the catch move. Either way the shackle stays trapped until the barrier clears.

Combination locks are often overrated, because a lock with a few wheels has a limited number of settings and can be worked through by feel or sound. Keyed versions expose a keyway that can be picked. The honest comparison is against convenience: such a lock mostly discourages casual opening rather than determined attack.

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.