a part of a machine that allows movement in one direction only. It is usually a wheel with teeth-like parts that either slide over or lock against the free end of a bar.
The ratchet at the other end of the axle only turns one way.
Keep the ratchet mechanism lubricated with oil.
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Most handbrakes need about four clicks on the ratchet -if yours takes much more, a garage should adjust it.
Catapults were loaded and cocked by means of large wheels with ratchets.
Walnut leaves have a jagged sawtooth edge rather like a ratchet.