38" wheels are used on 150 ton capacity cars, primarily the center connection trucks on modern intermodal cars with 33" wheels at the coupler ends.
Nickel Silver Plated Brass Insulated Wheelsets These wheels follow NMRA RP-25 Standards. One wheel is insulated from the all-metal axle. The entire wheelset is non-magnetic. The axle length is 1.006" (+- .004")