I just picked up a set of SRP pistons but I cant seem to find any part number on it (don't know if they even come with one) The only markings I've found are on the bottom of the piston. I took a pic to show what I am talking about. They are supposed to be 81mm but I do not understand why there would be a 20 stamped on them. I do not know much about SRP pistons so I am learning any help/info on this would be greatly appreciated. Thanks