Hello, Peter. Thanks for the reply. Both are non-magnetic. By weight the 2 in the back are much heavier , the fractional index weighs 21.5 ounces , and the number set weighs 20.5 ounces. I would have guessed the other way around, seems like more metal was removed for the larger holes?? The one in front weighs the least, at 17.6 ounces, I will go with the zinc die cast for the letter index. With the weight difference, I will go with bronze for the other 2 . Now it's time to get the bits cleaned up!! Seems like a lot more work was put into the 2 in the back, the holes in the bottom were tapped, but the letter index has the holes, but are not tapped.Thanks, Lou