The teeth on a helical gear cut at an angle to the face of the gear. When two of the teeth start to engage, the contact is gradual--starting at one end of the tooth and maintaining contact as the gear rotates into full engagement. Helical gears operate more smoothly and quietly compared to spur gears due to the way the teeth interact. Helical is the most commonly used gear in transmissions. They also generate large amounts of thrust and use bearings to help support the thrust load.

An Anti-Backlash Gear is a gear having minimum or no backlash (lash or play). Anti-backlash capabilities can be applied to many types of gears, and is most commonly seen in spur gears, bevel gears and miter gears, and worm gears. Sometimes backlash is favorable and a necessary part of the way gears work, but in many situations it is desirable to have little or no backlash. This maintains positional accuracy, which is key in applications where items need to be mechanically lined up.

A gear rack is used with a pinion or spur gear and is a type of linear actuator which converts rotational motion into linear motion. The pinion or spur gear engages teeth on a linear "gear" bar called "the rack"; the rotational motion applied to the pinion causes the rack to move relative to the pinion, thereby translating the rotational motion of the pinion into linear motion.

An internal gear is a spur gear in which the teeth are machined on the inner circumference of an annular wheel, these mesh with the external teeth of a smaller pinion. Both wheels revolve in the same direction.  Internal gears have a better load carrying capacity than an external spur gear. They are safer in use because the teeth are guarded. They are commonly used on bicycle gear changing system, pumps and planetary gear reducers.

The most common gears are spur gears and are used in series for gear reductions. The teeth on spur gears are straight and are mounted in parallel on different shafts. Spur gears are the most common & cost-effective type of gear, which provides 97 to 99% efficiency to medium to high power to weight ratios.

The worm (in the form of a screw) meshes with the worm gear to engage the gears.  It is designed so that the worm can turn the gear, but the gear cannot turn the worm.  The angle of the worm is shallow and as a result the gear is held in place due to the friction between the two.

Worm gears are used in large gear reductions. The gear is found in applications such as conveyor systems in which the locking feature can act as a brake or an emergency stop.