IFMAR appropriate size, specially-designed 2WD/4WD back tires with 12mm interior hex. The guts countersunk area had been redesigned to put the wheel nut much deeper. Precision fit, ideal for high-competition race. Made from versatile, durable product to withstand effects. The inside for the wheel is aerodynamic for maximum performance. Moderate hardness. Special highlights of the wheel are noticeable from inside: reinforcement ribs to make the tires as stable as you are able to and expel deformation. Set of 5 pairs (10 pcs) the price of 4 pairs. Outstanding value pack. Fits all XB2 & XB4