33" smooth back wheels Accurate markings Incredible detail True to prototype Non-magnetic Metal wheels Highly Flexable sprung trucks Metal SideFrames & Bolsters Fully Sprung Smooth tracking Free rolling Contoured Insulated Axes RP-25 Free rolling wheels.The A. S. Foundries?« A-3 Ride Control?« 50-ton freight truck was introduced in the 1940's and is one of the forerunners of modern freight trucks. Features embodied into this design include a longer spring travel, no spring planks and constant friction control using friction castings in the bolster to dampen excessive lateral roll of the car. These design features allowed for a higher train speed with less danger of derailment than previous designs. ASF?« sold over 140,000 sets by 1949. This truck is excellent for modeling the transition era up to 1994 when friction bearings were no longer allowed in interchange service.KadeePart KAD504