Pinewood Derby Tungsten Cylinder & Ball Weights Set | Gravity Assist Heavy - Tungsten Carbide is denser than Lead or Zinc so your car can have a slim profile! Go fast - Cylinders allow precise placement in the car and the balls give you precise weight control. Look good - Weights can be hidden in the car by drilling a 3/8 dia. hole and filling with wood putty. Professional - Tungsten carbide is the same material used in high end drill bits. Non-toxic - Safe to Handle.