Confirmed layout for flap hinge pin retainer nutplates. Starting with right wing, drilled #40 pilot holes for rivet and screw. Enlarged screw hole to #30 and deburred both holes. Clecoed nutplate to inside of flap spar through rivet hole; inserted screw and tightened nutplate to spar. Removed cleco and countersunk rivet hole for flush head rivet. Set rivet to secure nutplate and removed screw.