Abstract: A ratchet mechanism comprising a rotatable member incorporating a toothed periphery, the rotatable member being suitably mounted to allow free rotation thereof, a pawl incorporating apparatus for engaging the toothed periphery, the pawl being suitably mounted to permit movement thereof from a position in which the pawl allows said rotatable member to rotate freely in either direction of rotation to a position in which the pawl prevents said rotatable member from rotating in one direction, and selectively operable apparatus to move the pawl between said positions, said selectively operable apparatus incorporating an over-dead-center spring arrangement to bias the pawl into the selected position.