The forward fuselage skin is dimpled for #6 screws where the skin attaches to the f-821afb, but the rivets are machine countersunk. Unfortunately, I didn’t take many photos during this. I will try to post a few when I next go to the shop. However, here is the process. The F-821afb will be sandwiched between the fiberglass instrument panel cover, and the forward fuselage skin. The #6 screws will attach to nut plates in the fiberglass parts. The AN426 rivets will simply hold the F-821afb in place. This requires a double flush rivet. Because we are using a double flush rivet, the bottom of the F-821afb is machine countersunk for the AN426 rivets, while the top of the F-821afb is machine countersunk to accept the #6 dimple. We don’t want to over countersink. If we dimpled the AN426 rivets, we would have to countersink both sides of the F-821afb where the AN426 rivets go. So, the preferred method is to countersink the forward fuselage skin. I did this with the forward fuselage skin clecoed in place, and the F-821afb clecoed in place. This way I could be sure the countersink would not chatter, and if any additional countersink occurred (which it did not) it would take material out of the F-821afb. This will all be much easier to see with a picture, so I’ll be sure to post one soon.