Pin tumbler lock

Five pin stacks jam the plug. Springs push them down. The right key lifts every gap to the shear line, and the plug turns.

• Gold pins ride the key. Steel pins sit above them.
• A deep cut lets its pin drop. A shallow cut lifts it.
• Too low: the steel pin blocks. Too high: the gold pin blocks.
• Try the wrong key. Two pins miss by 0.6–0.8 mm. That is enough.
• Hatched faces are the cut. Real locks use 5–6 pins and 0.4 mm depth steps.