A system and method of assembling flanged duct sections, using large sheet metal screws through opposing inserted corner plates. The large screws are threadedly inserted fully through the corner plates of a first duct section and hold perpendicular thereto for guiding alignment with the mating duct section. The screws hold the duct sections apart to allow aligning them without fluid sealant or tape gasket material on one of the duct sections contacting the other. The screws are then threadedly engaged with the corner plates of the mating duct section, bringing the duct sections together with a leak resistant seal therebetween. Optional hanger brackets can be placed between the corner plates before assembly, and additional screws used to deform the flanges and corner plates about the brackets to compress the sealant or gasket thereabout.