Backing T 12T C C - Section Patch 3T Backing Framing member Clamp and bond backing to frame and skin B B - Section Patch Backing Clamp and bond backing to frame and skin 12T 3T T 30T 12T T Plywood saddle gusset minimum  thickness “T” bonded in place A A - Section Patch 3T (¼" minimum) 8T T T 12T D D - Section 3T Waxed paper or  plastic wrap Nailing strips C C C C B B A A B B D D C C Nailing strips Maximum diameter 25T Temporary backing Minimum thickness bonded in place T Saddle Gusset Temporary backing block-shape to fit skin Figure 6-33. Scarf patches, back of skin accessible. 6-25