Spur gears are the most typical type of gears. They have straight teeth, and so are installed on parallel shafts. Occasionally, many spur gears are used at once to create very large gear reductions.

Spur gears are used in many devices that you could see around HowStuffWorks, like the electric powered screwdriver, dancing monster, oscillating sprinkler, windup noisy alarms, washer and clothes dryer. But you won’t find many in your car.

This is since the spur gear can be really loud. Each time a equipment tooth engages a tooth on the other gear, the teeth collide, which impact makes a noise. It also increases the stress on the gear teeth.

To reduce the noise and stress in the gears, most of the gears in your car are reducers for greenhouse helical.