A reduction gear is part of a mechanical system of gears and shafts that serves the primary purpose of slowing things down within a machine so that energy one place can be transferred and used in another. Reduction gears are most commonly seen in car and truck drivetrains, and in these settings they reduce the high rotational speeds of the engine and convert them to a usable, slower speed that the tires can interpret and safely use. These sorts of gear configurations are also frequently used in heavy machinery and other mechanical appliances both large and small. Anything that uses high rotational speeds in one place but needs energy reduced in another can make use of this sort of internal system. When the gears are working properly, the rotational speed of the input shaft converts to a slower rotational speed on the output shaft. This reduction in output speed helps increase increase torque. The system can look slightly different in different settings, but the concept is usually the same.