IFMAR appropriate size, specially-designed 2WD/4WD back tires with 12mm inside hex. The center countersunk area had been redesigned to place the wheel nut more deeply. Precision fit, ideal for high-competition racing. Created from flexible, durable material to withstand impacts. The medial side related to wheel is aerodynamic for maximum performance. Medium hardness. Unique options that come with the wheel are noticeable from inside: reinforcement ribs to help make the tires as stable as you possibly can and eliminate deformation. Number of 5 pairs (10 pcs) the cost of 4 pairs. An excellent value pack. Fits all XB2 & XB4