are the casing for gear sets that transmit power from one rotating shaft to another. A gear box has a number of functions: it is precisely bored to control gear and shaft alignment, it contains the gear oil, and it protects the gears and lubricant from water, dust, and other environmental contaminants. Gear boxes are used in a wide range of industrial, automotive, and home machinery, e.g., paper mills, automotive transmissions, electric mixers. Not all gears are enclosed in gear boxes; some are open to the environment and are commonly lubricated by highly adhesive greases.

Also see open gear.