Pg. 21-05 Step 12: Riveted the remaining Flaperon Stop and Flaperon Mixer Assy. to the Rt. Seat Rib Assy. Step 13: Riveted the Rt. Seat Rib with Nutplates to the Flaperon Mixer Arm Assy. Deburred and primed two each Crotch Strap brackets. Pg. 21-06 Step 1: Dimpled the nutplate holes for two F-1276A Crotch Strap Brackets and machine countersunk the nutplate holes for two F-1276B Crotch Strap Brackets. Step 2: Dimpled the nutplates, then riveted the nutplates in place for the four brackets. Step 3: Dimpled the #30 hole in slope of the remaining Rt Seat Rib. Step 4: Riveted an A & B Crotch Strap Bracket to Flaperon Mixer Bracket/Seat Rib Assy. and the remaining Rt. Seat Rib. Step 5: Dimpled the four #30 holes in the sloped flange of the remaining Lt. Seat Rib. Step 6: Riveted the remaining A & B Crotch Strap Bracket to the Pulley Bracket/Seat Rib Assy. and Lt. Seat Rib.