Drilled 4 holes in in the sheet same as skin and flat aluminum, then dimpled skin as per normal. I contersunk 1 hole very deep at .016 below surface, 1 hole at .009" and 2 at 0.007". When clecoed together 2 holes at 0.007 slightly lifte the skin. After back riveting 4 rivet and inspecting I can tell that there is no big difference between 0.009" and .0007" both are good quality; however 0.016 rivet sits good but it has some space between rivet head and dimple.
