Here is the rudder skin, with stiffeners riveted to the left side.

You can see the holes in the right side of the skin where the stiffeners will be riveted.

The rudder has very little internal structure, so the purpose of the stiffeners is to keep the large areas of unsupported skin from vibrating.

The inside of the skin is an olive drab colour because of the anti-corrosion primer.

The rivet gun is sitting on the table in the foreground.