I spent all day countersinking today. All those holes in the spars needed to be countersunk as the wing skins will sit flush against the spar flanges. They either had to be countersunk for rivets that hold nut plates on, for access plate screws, tank screws (the fuel tanks are held onto the plane with screws), and just normal dimpled skins.
The end result is a spar that’s looking good and ready to go, and a new case of carpel tunnel.