Countersunk the spar for riveting per the plans. The first picture shows a typical nutplat rivet countersunk flush to the spar, with a test rivet in place. For the locations under the wing skin, I made a test peice of .032 with a #40 hole dimpled as the skin would be. The second picture shows it in use. The third picture shows how a test rivet looks in the slightly deeper countersink needed to accomodate a dimple. After doing all the flange countersinks, I final-drilled and countersunk the holes at the root end of the web.