so im looking at pistons to buy and its listing diffrent mm sizes. theres 84.0mm 84.5mm and 85.0mm so im wondering is 84.0mm the stock size and the 84.5mm and 85.0mm is for bored over engines or.....what? i thought when you bored a motor it went by .20 over and .30 over and so on? also if the larger piston mm are the bored over sizes should i send it to a place that bores them by mm? thanks in advance for any help.