<P> Because the ratchet can only stop backward motion at discrete points (i.e., at tooth boundaries), a ratchet does allow a limited amount of backward motion . This backward motion--which is limited to a maximum distance equal to the spacing between the teeth--is called backlash . In cases where backlash must be minimized, a smooth, toothless ratchet with a high friction surface such as rubber is sometimes used . The pawl bears against the surface at an angle so that any backward motion will cause the pawl to jam against the surface and thus prevent any further backward motion . Since the backward travel distance is primarily a function of the compressibility of the high friction surface, this mechanism can result in significantly reduced backlash . </P> <P> Ratchet mechanisms are used in a wide variety of applications, including these: </P> <Ul> <Li> Capstans </Li> <Li> Clocks </Li> <Li> Freewheel (overrunning clutch) </Li> <Li> Jacks </Li> <Li> Anti-rollback devices used in roller coasters </Li> <Li> Slacklines </Li> <Li> Tie down straps </Li> <Li> Turnstiles </Li> <Li> Handcuffs </Li> </Ul> <Li> Freewheel (overrunning clutch) </Li>

How to change directions on a socket wrench