Specified pitches and sales opportunities of the worm do not permit the worm gear to travel the worm. This is helpful when the software requirements to lock the output if the software is managing in the reverse route. When the helix angle is less than 5°, the worm is self-locking. When the helix angle is higher than 10°, the worm can be driven back. Worm and worm gear assemblies need to be mounted on vertical, non-intersecting shafts.