a railroad car wheelset has an axle with one wheel rigidly attached . this wheel is permitted to rotate by means of journal bearings either on the extreme ends of the axle or inboard of each wheel location . at the other wheel , the axle has smooth surface and a self - lubricating bearing is provided as a part of a hub on the axle . the hub is integral with the axle or press fit thereon . the axle has a boss for preventing the independently rotating wheel from migrating laterally out of proper alignment . a self - lubricating thrust bearing is located between this boss and the side of the wheel to eliminate any possible galling between the two moving surfaces .