Nutplate countersinking for fuel tank and aileron

Deburring tool: 120 degree with #40 guide. The depth was made sufficient for the stainless steel rivets to lie flush. This meant the holes in the aileron rib become slightly larger then 2.5mm, namely 2.8mm, owing to the thinness of this rib. For the fuel tank back ribs there was about 0.5mm thickness remaining at the bottom of the countersink.