Then you are suppose to make these little shims for the aft end of the ribs that go in between the rib tab and skin. The skin is folder into a spar. But, thanks to brother Ed pointing out that the skin is not snug against the ribs, I first match drilled the hole thru skin into the rib to hold it snug. Otherwise I would end up with bad positioning of the rear rivet that goes through the folded spar and into the aft tab of the rib.
