Hey Hawk,
If you look at the one split bone that's on its edge, you'll notice that the end is sanded down at a bit of an angle. I use the leading edge of those ulna bones for notching my points or putting deep serrations on the edges. They work best on small, thin arrowpoints, and since that's what I make the most of, the ulna bones work well. They can't be used for notching larger points because so much pressure must be used that the ends tend to splinter, ruining the tool. But even when notching small arrowpoints, sometimes I crush the edge inside the notch, making any more flake removals impossible. In that case I'll fudge and use my horseshoe nail tool to re-establish my edge, then go back to the ulna bone.
