Gearboxes
A gearbox is the gear system that transmits mechanical power from a prime mover (which can be an engine or electric motor), to some form of useful output device. Typically, the rotational speed of an input shaft is changed, resulting in a different output speed. However, some of the simplest gearboxes merely change the physical direction in which power is transmitted.

Most gearboxes will either reduce an unsuitable high speed and low torque of the prime mover output shaft to a more useable lower speed with higher torque, or do the opposite and provide a mechanical advantage (i.e. increase in torque) to allow higher forces to be generated. Many systems include the ability to select one of several different gear ratios. In this case, most of the gear ratios (simply called "gears") are used to slow down the output speed of the engine and increase torque. However, the highest gear(s) may be an "overdrive" type that increases the output speed.

In selecting a gearbox, one must be mindful that gearbox selection will impact more than just the output speed and torque level at the output shaft. Some of the considerations to keep in mind should include:

* Load
* Environment
* Gear Ratio
* Input Speed
* Horsepower
* Direction of Rotation
* Mounting Style