In this work session, I riveted together the end ribs, and the upper skin of the left flap. I was able to access the internal ribs by using the side of the squeezer yoke as a flat steel bucking bar. I also used the squeezer to set the rivets on the inboard rib, then squeezed the skin rivets that affixed the inboard end rib into place. The outboard rib was installed using the rivet gun and the bucking bar.