Gears are a crucial component of many motors and machines. Gears assist in torque output by providing gear reduction and they adjust the path of rotation like the shaft to the rear wheels of automotive automobiles. Here are some simple types of gears and how they are different from each other.
Spur gears are 
mounted in series on parallel shafts to accomplish large gear reductions.
The most typical gears are spur gears and so are found in series for large gear reductions. The teeth on spur gears are straight and are mounted in parallel on different shafts. Spur gears are used in washing machines, screwdrivers, windup alarm clocks, and other devices. These are particularly loud, due to the equipment tooth engaging and colliding. Each impact makes loud noises and causes vibration, which is why spur gears are not used in machinery like cars. A normal gear ratio range is 1:1 to 6:1.
Helical gears operate more smoothly and quietly compared to spur gears due to the way the teeth interact. One’s teeth on a helical gear cut at an angle to the face of the apparatus. When two of the teeth start to engage, the contact is gradual–beginning at one end of the tooth and maintaining contact as the gear rotates into full engagement. The typical selection of the helix angle is approximately 15 to 30 deg. The thrust load differs straight with the magnitude of tangent of helix angle. Helical may be the most spiral bevel helical gearbox commonly used equipment in transmissions. In addition they generate huge amounts of thrust and use bearings to greatly help support the thrust load. Helical gears can be utilized to adapt the rotation position by 90 deg. when installed on perpendicular shafts. Its normal equipment ratio range is 3:2 to 10:1.
Bevel gears are used to change the path of a shaft’s rotation. Bevel gears have tooth that are available in directly, spiral, or hypoid form. Straight teeth have similar features to spur gears and possess a large impact when engaged. Like spur gears, the standard equipment ratio range for directly bevel gears is 3:2 to 5:1.
Spiral teeth operate the same as helical gears. They generate less vibration and noise when compared to straight teeth. The proper hands of the spiral bevel may be the external half of the tooth, inclined to visit in the clockwise direction from the axial plane. The left hands of the spiral bevel travels in the counterclockwise path. The normal equipment ratio range is 3:2 to 4:1.
In the hypoid gear above, the larger gear is called the crown as the small gear is named the pinion.
Hypoid gears are a kind of spiral gear in which the shape is a revolved hyperboloid rather than conical shape. The hypoid equipment areas the pinion off-axis to the band equipment or crown wheel. This enables the pinion to be larger in diameter and offer more contact area.