Fan spacer size?

cast aluminum uses a 3" deep pulley and the iron uses a 2 11/16 pulley. I shoot for 1" away from the radiator. I have seen at least 4 or 5 different length spacers. it all depends on the application. those spacers were used all across the board for all car and truck lines. it will also depend on whether or not you use a clutch or solid mount fan