Match drilled through the U support bracket and cover into the carrythrough spar flanges.

With the #30 holes already in the cover and carrythrough spar flanges, as well as the #19 holes for attaching the U bracket, there were already enough holes that I didn't want to drill anymore through those carrythrough spar flanges for nutplate attachment. Instead, I decided to make this little plate to which I will rivet the nutplates. This, in turn will be riveted to the carrythrough spar flanges with only two rivets out near the ends.

Because one of the pop rivets will be covered up with the U bracket on each side of the cover, I countersunk those two holes with a 120 degree countersink so they will accept CS4-4 rivets instead the specified LP4-3 rivets.

When countersinking those holes noticed that the #19 holes in this cover had become elongated while match drilling into the carrythrough spar flanges. This means that the U bracket I had so carefully fabricated will now have to be slightly twisted to align with the holes. Very frustrating. I should have used the little brass guide bushings to transfer drill those holes in several smaller steps. Grrr.

Drilled the cover and U bracket for a 1/4" bolt and drilled and countersunk for a 1/4 nutplate to be riveted to the cover.