Manufacture of aileron balance tube washers

When drilling and test fitting the aileron balance tubes, it was noticed that a snug fit of the tube into the circular notches at the front of the ribs was absolutely mandatory to be able to close the leading edge of the skin. At the same time the skin would also stand off from the tube at the positions of the holes provided for rivetting the skin to the tube, by about 1.6-2mm. This gap would vary slightly along the length of the tube. So rivetting these holes would actually cause the skin to likely dimple at these points, or at least the rivet to upset between the tube and the skin, which is not so desirable.

So some curved washers were made from 1.6mm 6061-T6 to simultaneously fill this gap and allow for a bit of movement of the skin, while minimising the dimple formed when rivetting.