Bevel gears are useful when the path of a shaft’s rotation must be changed. They are often mounted on shafts that are 90 degrees aside, but could be designed to work at additional angles as well.
The teeth on bevel gears can be straight, Water-lubricated Air Compressor spiral or hypoid. Straight bevel gear teeth actually have the same issue as straight spur gear teeth — as each tooth engages, it impacts the corresponding tooth all at once.
Just like with spur gears, the perfect solution is to the problem is to curve the gear teeth. These spiral tooth engage exactly like helical teeth: the contact starts at one end of the gear and progressively spreads over the whole tooth.
On direct and spiral bevel gears, the shafts should be perpendicular to one another, but they must maintain the same plane. In the event that you were to expand the two shafts past the gears, they would intersect. The hypoid gear, however, can build relationships the axes in various planes.
Hypoid bevel gears in an automobile differential
This feature is used in many car differentials. 
The ring gear of the differential and the insight pinion equipment are both hypoid. This allows the insight pinion to be installed lower than the axis of the ring gear. Figure 7 displays the insight pinion engaging the band gear of the differential. Because the driveshaft of the car is connected to the insight pinion, this also lowers the driveshaft. This implies that the driveshaft doesn’t intrude in to the passenger compartment of the automobile as much, making even more room for people and cargo.