This information on different types of gears. I had to do a speech about gears. Thought it might be useful for someone else.

Gear, toothed wheel or cylinder used to transmit rotary or reciprocating motion from one part of a machine to another. Two or more gears, transmitting motion from one shaft to another, constitute a gear train. At one time various mechanisms were collectively called gearing. Now, however, the word gearing is used only to describe systems of wheels or cylinders with meshing teeth. Gearing is chiefly used to transmit rotating motion, but can, with suitably designed …

…A worm gear is a long, thin cylinder that has one or more continuous helical teeth that mesh with a helical gear. Worm gears differ from helical gears in that the teeth of the worm slide across the teeth of the driven gear instead of exerting a direct rolling pressure. Worm gears are used chiefly to transmit rotation, with a large reduction in speed, from one shaft to another at a 90° angle.