So, why does the bolt going through the flap actuator cover need to be recessed? And why is there an extra washer used on the bolt at the nut end? I see why now. It’s all about getting the hole in the bolt for a cotter pin to be in the proper position for the castle nut. As can be seen in image 1, the hole in the bolt is in perfect position in relation to the castle nut. Without the bolt head recess and extra washer at the nut end the hole isn’t in proper position.
The F-766C doubler plate attach rivets need to be flush so the flap actuator cover can sit flush on this channel. So I dimpled the channel and counter sunk the doubler.
