An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported.
The axle shafts used in vehicles—also called half shafts or CV axles—allow the transmission to transfer motion to the vehicle's wheels. Axle shafts also regulate changes in drive between the differential sun wheel and rear hub.
An entire axle assembly typically contains two half shafts located on each side of the differential. They are connected to the wheel bearing and allow the wheel to rotate. They may also be found in machines that require physical components to rotate, such as gears.