They came with both. Put a magnet on it or just look at it; steel will rust and aluminum won't. I'm guessing you're asking because you may be looking at purchasing U-joints and it has the option of steel or aluminum driveshaft? If that's the case, the U-joints are the same size. The one's for the aluminum shaft are coated to help prevent corrosion from what I remember and they'll work in the steel shafts just as well.