ratchet and pawl, mechanical device that permits motion in one direction only. The ratchet is usually a wheel with slanting teeth. The pawl is a lever tangential to the wheel with one end resting on the teeth. When the wheel rotates one way, the pawl slides over the teeth; when the wheel rotates the other way, the pawl catches in the teeth.

Mechanical device that transmits intermittent motion or permits a shaft to rotate in one direction but not in the opposite one. Reversible ratchets are used on socket wrench handles and are convenient for tightening or loosening bolts in positions where a complete revolution of a wrench handle is impossible. They are used in mechanical jacks to lock the jack rod after each successive lift.

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