WISECO FORGED PISTONS 4.030 BORE SIZE FOR SBC 383 ENGINES,-12cc RD DISH TOP FOR USE WITH 5.7 BUSHED OR PRESS FIT RODS.030 OVER. The next level up would be the professional series that are much more expensive and made from 2618 aircraft alloy and have fully machined crowns rather than the as cast crowns that are on the Pro-Tru series.