There have been many sanding blocks over the years and the True-Flat is by far the best. Either size will give you a consistant, flat sanded surface. Your car's body will be smooth enough to paint any color, even black. Made from 100% real rubber, and available in 5in. x 2-1/2in. and 9in. x 2-1/4in.. These sanding blocks allow you to use sheet sand paper economically.