Particular pitches and leads of the worm do not permit the worm equipment to drive the worm. This is valuable when the software needs to lock the output if the software is operating in the opposite course. When the helix angle is much less than 5°, the worm is self-locking. When the helix angle is greater than 10°, the worm can be pushed again. Worm and worm gear assemblies have to be mounted on vertical, non-intersecting shafts.