Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used simultaneously to create large gear 
reductions.
Spur gears are found in many products that you can see around HowStuffWorks, like the electric screwdriver, dance monster, oscillating sprinkler, windup alarm clock, washer and clothes dryer. But you won’t find many in your Screw Air Compressors vehicle.
This is since the spur gear could be really loud. Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a sound. In addition, it increases the pressure on the gear teeth.
To lessen the noise and stress in the gears, the majority of the gears in your car are helical.