The self-centering action trucks self align themselves parallel with the car for easier placement on track. Mounts with a #2 or 2-56 screw. The Bettendorf double truss truck was introduced in the 1930s by U.S. railroads and was allowed to be used in interchange service through 1993. The Kadee #500, #502 and #550 represent 50-ton trucks for 100,000 pound cars Truck Features: * Self Centering Action - Trucks self align themselves parallel with the car for easier placement on track * Code 110 (.110) 33 smooth back wheels * Accurate markings * Incredible detail true to prototype * Non-magnetic metal wheels * Highly flexible sprung trucks * Metal side frames and fully sprung bolster * Smooth tracking free rolling contoured insulated axles * RP-25 free rolling wheels