10 or 12 is the conrod bearing inner size, you can't change nothing. If you have a crankshaft with 12mm rod bearing inner size, you must buy stage6 racing 12, because the 12 version piston is different ( pin has 12mm instead of 10). If your crankshaft is 10mm, i must buy s6r 10 version, or buy another crank, because 10mm bearing with such rotation there's no a good idea...