Worm gears use screw threads to reduce shaft speed by ratios of 18:1 and greater while transmitting motion at a right angle.

Also known as spiral miter gears, these gears have curved teeth that gradually engage and stay in contact longer than straight teeth so they handle heavier loads at higher speeds. Speed ratio is 1:1.

For smooth, quiet operation at high speeds under heavy loads, helical gears have curved teeth that engage gradually and stay in contact longer than straight teeth.

Transmitting loads at higher speeds than spur gears in environments where rusting and exposure to chemicals is a concern, these plastic gears have helical teeth, which stay in contact longer than straight teeth. They’re often called screw or crossed-helical gears.