Outer edge of doubler Nail holes Screw holes—to be filled before finishing Butt joint of patch to skin Plywood skin Saw cut in doubler Plywood doubler Plug patch Inner edge of doubler Saw cut in doubler Butt joint of patch to skin Grain direction of skin, patch, and doubler  A B C (Two rows of screws and nails are required for a large patch.) (Laminate doubler from two pieces of  1 ∕ 8 " ply in areas of skin curvature.) ¼ " 2  5 / 8 " 2" 1 ³ / 8" 3  7 / 8" 3" 2  1 / 8" Small circular plug patch Large circular plug patch A B C DIMENSIONS Figure 6-31.  Round plug patch assembly. 6-23