The AN509 screws that attach the counterweight to the counterbalance rib are flush screws. I dimpled the forward two holes in the counterbalance rib using a #10 dimple die and countersunk the counterweight to accept the dimple in the rib using my countersink cutter.
On the left and right rudder skins, I dimpled the aft most hole in the top of the skins for a CS4 flush rivet. The head on this rivet has a 120 degree angle as opposed to the 100 degree angle for AN426 flush rivets. I used a 120 degree dimple die to dimple these holes so that the head of the rivet can be set correctly when these holes are riveted. The rest of these holes will get dimpled later when the rudder tip is attached to the rudder.
