Abstract: A sheet metal duct section component including at least one pair of adjacent longitudinally extending integral panel portions relatively angulated about a longitudinal zone connecting adjacent longitudinal marginal portions of said panel portions. At least one pair of corresponding ends of the panel portions include individually bendable flanges extending endwise outwardly therefrom. The flanges are bent relative to and toward corresponding sides of the panel portions into generally coplanar relation and include outer end extremities bent backwardly over the flanges to define double thickness flanges. A filler plate of a thickness at least generally equal to the double thickness flanges and including an outside corner defined by adjacent relatively angulated marginal edges of the filler plate is provided and substantially conforms to the inside corner defined by the adjacent marginal portions of the double thickness flanges.