I have a 110/74 Sugino triple crankset on my touring bike (83 Trek 520). I want to move my middle 45t ring to the outer posistion (I tried it, it works) and need to buy a 37t for the new middle. Can I use a bmx chainring? they are cheaper and widely available than sugino rings. I'm puzzled why many online vendors don't list the bmx rings with the other ones. Are they thicker or somehow only workable as a single ring?