Tool for generating a rotary movement.

Ratchet is the name given to a screwdriving tool which – unlike a standard wrench – does not have to be reapplied every time there is not enough space to complete a full turn with the wrench in place.

To tighten or loosen a screw connection step by step, the ratchet is instead repeatedly moved back and forth through a certain angle (= operating angle).

The ratchet transmits the manual force in one direction of rotation directly to the nut or bolt. In the counter-rotating direction, however, no force is transmitted, but the ratchet rotates freely, producing a mechanical creaking or snapping noise at the same time. To make the tool suitable for both unscrewing and screwing, this function can be switched with a small lever or rotating ring on the ratchet head so that the respective directions of rotation for (creaking) idling and (silent) power transmission are reversed.

[Wikipedia / Further explanation: en.wikipedia.org/wiki/Socket_wrench]