1/8" axle, exacting reproduction of the original Russkit Pro-Racing rear wheels. Note that these were not used on any Russkit kits or RTR cars are were made available for professional racers to have a wider wheel for cars under different regulations. Uses 4-40 setscrew (not supplied). O.D. 0.625", diameter at rim where the tire mounts is  0.550", width between rim beads 0.490", overall width with setscrew boss is 0.700". Fits foam donuts as well as Ortmann Monogram and K&B "Series 2" reproduction rear tires. Will fit most vintage cars as well as pro-racing cars and reproduction of such.