I figured the notches looking slightly different would account for a slightly different "X". Thus the numbers would correspond to the size you wanted. But there is so little variation that it doesn't seem right for a hand tool. Unless it's to accommodate a different size head you are rapping. Which could be just slightly different in size. Did anyone else see that "splash tool" that is used for making a design on the rivet heads used in the making of trunks? I don't think this is a splash tool, but I still think it's for moving along and rapping with a hammer, the short leg being used as a guide.