This provides the bearing between the axle and on all railway vehicles frame. These were usually simple bearings designed to take the load (for driving wheels) of the alternating piston thrusts as well as the weight of steam locomotive. They were mounted in vertical slides within the frames and sprung to allow for uneven track. Relying upon a simple film of oil for lubrication, it was not uncommon for an axle box to overheat and seize (hence the term `hot box’).