An Axle Shaft is a bar on which a wheel, pair of wheels, or other rotating member revolves. In other word, a shaft of a driving axle of a self-propelled wheeled vehicle that transmits rotation from the differential gear to a driving wheel.
A distinction is made between full-floating and semi-floating axles. In a full floating axle, the axle shaft passes freely through an opening in the differential housing, which is mounted on the bearings of the driving axle; the differential housing is connected by a flange to the boss of the driving wheel, whose bearings are attached to the axle housing. All the longitudinal and transverse forces are taken up by the axle housing, and the axle shaft is subject only to torsion. A semi floating axle has a driving wheel fixed to its end which is subject not only to torsion but also to bending forces from the driving wheel.
Moreover, full-floating axles are used in trucks, buses and heavy, wheeled tractors; whereas semi floating axles are used in automobiles, in which the load on the wheels is relatively small.