Pro-Line Gear Drive Sets Pro-Line dual gear timing sets are manufactured from 8620 low carbon nickel-chromium-molybdenum steel billet. The state-of-the-art CNC machine centers provide accuracy and precision tolerance. All gear teeth are crown shaved for a smooth and quiet operation. The deep carburizing of the gear to HRC60 is made for the toughest operation. Comes with instructions. Fits any block.