Sprag clutch
A sprag clutch is a one-way freewheel clutch.
It resembles a roller bearing, but instead of cylindrical rollers, non-revolving asymmetric figure-eight shaped sprags are used. When the unit rotates in one direction the rollers slip or free-wheel, but when a torque is applied in the opposite direction, the rollers tilt slightly, producing a wedging action and binding because of friction. The sprags are spring-loaded so that they lock with very little backlash.