Because spiral bevel gears don’t have the offset, they have less sliding between the teeth and are more efficient than hypoids and create less heat during procedure. Also, among the main benefits of spiral bevel gears is the relatively massive amount tooth surface that is in mesh during their rotation. Because of this, spiral bevel gears are a perfect option for high rate, high torque applications.
Spiral bevel gears, like other hypoid gears, are designed to be what is called either right or left handed. A right hand spiral bevel equipment is defined as having the external half a tooth curved in the clockwise path at the midpoint of the tooth when it is viewed by looking at the face of the gear. For a left hands spiral bevel equipment, the tooth curvature will be in a counterclockwise direction.
A gear drive has three main functions: to improve torque from the driving equipment (motor) to the driven products, to lessen the speed generated by the motor, and/or to change the path of the rotating shafts. The connection of the equipment to the apparatus box can be accomplished by the use of helical spiral bevel gear motor couplings, belts, chains, or through hollow shaft connections.
Velocity and torque are inversely and proportionately related when power is held continuous. Therefore, as speed decreases, torque boosts at the same ratio.
The heart of a gear drive is obviously the gears within it. Gears operate in pairs, engaging each other to transmit power.
Spur gears transmit power through shafts that are parallel. The teeth of the spur gears are parallel to the shaft axis. This causes the gears to create radial reaction loads on the shaft, however, not axial loads. Spur gears have a tendency to become noisier than helical gears because they work with a single line of contact between tooth. While the the teeth are rolling through mesh, they roll from connection with one tooth and accelerate to contact with the next tooth. This is unique of helical gears, 
that have more than one tooth connected and transmit torque more easily.
Helical gears have teeth that are oriented at an angle to the shaft, as opposed to spur gears which are parallel. This causes several tooth to be in contact during procedure and helical gears can handle holding more load than spur gears. Because of the load sharing between teeth, this arrangement also allows helical gears to use smoother and quieter than spur gears. Helical gears produce a thrust load during operation which needs to be considered if they are used. The majority of enclosed gear drives use helical gears.
Double helical gears certainly are a variation of helical gears in which two helical faces are placed next to one another with a gap separating them. Each face has identical, but reverse, helix angles. Having a double helical set of gears eliminates thrust loads and offers the possibility of sustained tooth overlap and smoother procedure. Like the helical gear, dual helical gears are commonly used in enclosed gear drives.
Herringbone gears are extremely like the double helical gear, but they don’t have a gap separating both helical faces. Herringbone gears are usually smaller than the comparable double helical, and so are ideally suited for high shock and vibration applications. Herringbone gearing isn’t used very often due to their manufacturing complications and high cost.
While the spiral bevel gear is truly a hypoid gear, it is not always viewed as one because it doesn’t have an offset between your shafts.
One’s teeth on spiral bevel gears are curved and have one concave and one convex side. They also have a spiral angle. The spiral angle of a spiral bevel gear is defined as the angle between your tooth trace and an element of the pitch cone, similar to the helix angle found in helical gear teeth. In general, the spiral position of a spiral bevel gear is defined as the mean spiral angle.