its refers to the fineness, ask for four ought steel wool or you'll see four zeros highlighted on the bag. great for anything chrome too. and remember that the chemical is harmful use gloves if you dont want messed up fingers. im assuming he will hit it with acetone before he paints, if not you should. welcome to the forum. what are you building?
oh the meth is so you stay on task and do one hell of a job. {dont do meth}