Certain pitches and leads of the worm do not permit the worm gear to travel the worm. This is helpful when the application demands to lock the output if the application is managing in the reverse route. When the helix angle is considerably less than 5°, the worm is self-locking. When the helix angle is better than 10°, the worm can be pushed back. Worm and worm gear assemblies must be mounted on vertical, non-intersecting shafts.