Drip Cap. Mill-finish aluminum drip cap diverts rain and melting snow from doors and windows. Used to protect door and window openings of all types including mobile homes, RVs, horse trailers, portable toilet enclosures, etc. With formed ends and punched screw holes. Note: measure lengths from inside the curve, as illustrated. The overall length equals the illustrated inside length + 3.5" . Inside length = 21" .