Tubular pin tumbler lock

The key pins (red) and driver pins (blue) are pushed towards the front of the lock, preventing the plug (yellow) from rotating. The tubular key has several half-cylinder indentations which align with the pins.

The protrusion on top of the key fits into the rectangular recess in the lock, causing the indentations to properly align with the pins. When the key is inserted, the gaps between the key pins (red) and driver pins (blue) align with the shear plane separating the plug (yellow) from the outer casing (green).

With the pins correctly aligned, the lock may turn.