A gear is a rotating machine part having cut teeth, which mesh with another toothed part to transmit torque. Geared devices can change the speed, torque, and direction of a power source.

Types of gears

Short answer:

• Parallel Axes / Spur Gear, Helical Gear, Gear Rack, Internal Gear.
• Intersecting Axes / Miter Gear, Straight Bevel Gear, Spiral Bevel Gear.
• Nonparallel, Nonintersecting Axes / Screw Gear, Worm, Worm Gear (Worm Wheel)
• Others / Involute Spline Shaft and Bushing, Gear Coupling, Pawl and Ratchet.

Long answer:

Spur gear

Parallel Axis Gear
In spur gears, the edge of each tooth is parallel to the axis of rotation and they mesh together when they are fitted to parallel shafts.


Helical Gear

A Parallel Axis Gear

The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle.
Advantages of the helical gear. Silent operation: In a helical gear train, the teeth engage a little at a time rather than the entire face at once. This causes less noisy power transfer in case of helical gears

Efficiency of helical gear is less because helical gear trains have sliding contacts between the teeth which in turns produce axial thrust of gear shafts and generate more heat.


Double helical gear

A Parallel Axis Gear

A herringbone gear, a specific type of double helical gear, is a special type of gear that is a side to side (not face to face) combination of two helical gears of opposite hands

Like helical gears, they have the advantage of transferring power smoothly because more than two teeth will be in mesh at any moment in time. Their advantage over the helical gears is that the side-thrust of one half is balanced by that of the other half.


Spiral bevel gear

Intersecting Perpendicular Axis Gears

Bevel gears are gears where the axes of the two shafts intersect and the tooth-bearing faces of the gears themselves are conically shaped.

A spiral bevel gear is a bevel gear with helical teeth. The main application of this is in a vehicle differential, where the direction of drive from the drive shaft must be turned 90 degrees to drive the wheels.


Metre gear


Metre gears are bevel gears has the same number of teeth on mating gears and with perpendicular axes specially used for 1:1 gear ratio.

Worm gear

Nonparallel and Nonintersecting Axis Gears.

A worm gear (or worm drive) is a specific gear composition in which a screw (worm) meshes with a gear/wheel similar to a spur gear. The set-up allows the user to determine rotational speed and also allows for higher torque to be transmitted.

Rack and pinion.

A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion.
The flat, toothed part is the rack and the gear is the pinion.

Gears are nothing but a way of transmitting power from one Shaft to another just like belt and pully drive or chain and sprocket drive. The advantage of gear drives over belt and pulley is that slipping is not possible in gear drives. So wear is less and it lasts for a longer period. Different speed ratios can be achieved by varying the number of teeth of the meshing gears creating a mechanical advantage.

According to the requirements, different gears are used in different fields. For instance

1. Spur gears are used to transmit power between parallel shafts. Helical gears are also used for the same purpose. The advantage of helical gear beeing less noise generation due to gradual contact between the meshing teeth. Again there are different types of helical gears available such as double helical gear, herringbone gear etc.
2. To transfer power between to intersecting Shafts bevel gears are used. Again to reduce noise spiral bevel gears are used.
3. For non intersecting and non parallel Shaft, hypoid gears are used. They look like bevel gears provided there axis do not intersect.
4. Worm gears are also used to transfer torque between two non intersecting and non parallel shafts. The main advantage of worm gears are that a high reduction can be achieved using this type of gears. They look like basic screw mechanism.
5. Rack and pinions are used to convert rotational motion to translation. Almost all the steering wheel of our cars contain rack and pinion to convert rotational motion of the steering to translational motion of the tierod.

Though there are a variety of gears that are available today, these are the major types which are being used.

Hope this will help. Thank you :)