On back of photograph: "Here the frame of the fin is 'dimpled,' i.e., the rivet holes are counter sunk so that the rivets will be flush with the surface skin and thus make for a smooth-flowing finished job. While this man 'dimples' the frame with a portable tool, his partner completes the same operation, by means of a press, on the skin, or metal sheets. Credit Courtesy of Fleetwings, Inc."
