I am at the stage on my Avanti that I need to drill the holes in the spar for the bolts that will retain the wing.
Since the "instructions" such as they are, don't even address this step, my thinking is to use a 4-40 bolt which will require drilling the hole in the wing a bit larger and then threading the hole in the wing skin as well as the spar with a 4-40 tap.
What have all of you used on yours?