A ratchet is a simple mechanical device consisting of a pivoted bar, or "pawl," resting on a toothed wheel or shaft designed so that the wheel can rotate in one direction only. If a second pawl is used an intermittent rotary motion can be transmitted. Ratchets are often parts of machine tools in which non-slip movement is essential. The rear sprocket of a free-wheelable bicycle incorporates a ratchet. See also lever.