Distribute weight to the best center of gravity (CoG) location and optimize the performance of your car. Screw-in, adjustable tungsten CoG weights make it possible to distribute weight quickly and easily. Test your racerís speed and fine-tune CoG weight placement with the included adjustment tool. CoG system is designed to fine-tune a carís center of gravity (1/2 inch to 1 inch forward of rear axle) and is not intended to overcome extreme weight distribution. Includes 3/8 inch drill bit. NOTE: Car kit with wheels shown in picture is an example of what can be built, but is not included.