Worm gear is also one kind of helical gear, which its shaft angle is general as right
angle, and the rod gear, which has one or multiple threads is one kind of helical gear,
its treads extend at least one turn. Generally be applied to deceleration devices,
machines tools, indexing devices, chain slings and so on.

Features of worm gear:
1. Larger ratio of a pair of gears
2. Less noise and vibration in operation
3. Self-locking function to prevent reversing
4. Two axises are not intersecting or paralleling, can be configured to90°