Tamiya Low Friction Plastic Double Rollers w/Rubber Rings Red & BlueThis product includes two each of red and blue 13 12mm double rollers with rubber rings. The 13mm roller side supports your car as it whizzes around the circuit, and when it turns the car leans and the 12mm roller takes over. In this way, your car gains great stability through corners, aided by the rubber rings slowing the car slightly when it comes into with the circuit wall. Screws, nuts, stabilizer balls, a hex wrench and more are included.