Spur Gear

They connect parallel shafts, have involute teeth that are parallel to the shaft and can have internal or external teeth. They cause no external thrust between gears. They are inexpensive to manufacture. They give lower but satisfactory performance. They are used when shaft rotates in the same plane.

Characterstics
The speed and change of the force depends on the gear ratio, the ratio of number of teeth on the gears that are to be meshed. One gear among the two is on the input axle, the axle of the motor and the other gear of the pair is on the output axle, the axle of the wheel.

Applications
Generally used in simple machines like washing machines, clothes dryer or power winches. They are not used in automobiles because they produce sound when the teeth of both the gears collide with each other. It also increases stress on the gear teeth.