The Pro-Wheel Shavers are precision devices that will shave time off your pinewood derby runs by: 1.Creating a wheel which is perfectly round, and true to the wheel bore. 2.Truing the inside edge of the wheel by removing molding marks and excess material. For more accuracy and ease of use, the Pro-Wheel Shaver XT is equipped with screw-adjustable blade depth! Just turn the knob to raise or lower the blade. Notes: 1.The Pro-Wheel Shavers are intended for use on wheels made of a hard plastic, such as those included in kits offered by BSA, PineCar, Royal Rangers, S&W, and Royal Ambassadors. The Pro-Wheel Shavers are not intended for use on wheels made of a soft plastic, such as those offered by Awana and PinePro. 2.A Pro-Hub Tool is required to use a Pro-Wheel Shaver.