A spiral bevel gear is a bevel gear with helical teeth. The helical design produces less vibration and noise than a conventional straight cut bevel gear. They will transmit more power in a given space than straight cut bevel gears. A spiral bevel gear set should always be replaced in pairs i.e. both the left hand and right hand gears should be replaced together since the gears are manufactured and lapped in pairs. Like straight cut bevel gears, spiral bevel gears are usually mounted at 90 degrees but can work at other angles except 0 and 180 degrees.
The main application of spiral bevel gears is in a vehicle crown wheel and pinion that houses the differential, where the direction of drive from the drive shaft must be turned 90 degrees to drive the wheels. They are also used in machine tools and reduction gearboxes.