Hand wheels are available for Screw Jack so that it can be easily used for manual operation. Hand wheels are used for self-lock equipped worm gear machine screw jacks only. Because ball screw jack and high lead screw jacks are not equipped with a self-lock, the input shaft may be reversed by a load, therefore, it is dangerous to use the hand wheel. Manually operating a jack when using screw jacks in intermittent positioning applications. Note: clockwise rotation with lift screw moves down(retract), counter-clockwise rotation with lift screw moves up(extend).