Abstract: A duct joining system having two L-shaped connectors for each duct corner. Each connector has two substantially perpendicular legs forming a corner region and has an inside and an outside surface with the outside surface of one L-shaped connector abutting the outside surface of the other L-shaped connector when the ducts are joined. An irregularly shaped opening is formed in the corner region of each L-shaped connector in alignment with the opening in the abutting connector. A tab having an enlarged head and a stem is integrally formed with and extends inwardly from the peripheral edge of each of the openings. A score line is formed at the base of the stem of each tab on the outside surface of the connector to allow the tab to be bent outwardly about the score line so that the tab can be inserted through the opening in the abutting L-shaped connector and than bent over to lock the connectors together.

Abstract: A duct joining system having two L-shaped connectors for each duct corner. Each connector has two substantially perpendicular legs forming a corner region and has an inside and an outside surface with the outside surface of one L-shaped connector abutting the outside surface of the other L-shaped connector when the ducts are joined. A orifice is formed in the corner region of each L-shaped connector in alignment with the orifice in the aubutting connector. A cleat is integrally formed with and extends inwardly from the peripheral edge of each of the orifices. A score line is formed at the base of each cleat on the outside surface of the connector to allow the cleat to be bent outwardly about the score line so as to extend through, and over the peripheral edge of, the orifice in the abutting L-shaped connector to lock the connectors together.

Abstract: A system for connectng the ends of sheet metal ducts wherein each duct end is provided with a frame. Corner connectors defining perpendicularly extending arms are associated with each frame, and bolts or other fasteners are utilized for connecting the connectors and frames. The respective frames comprise integral roll-formed sections at the duct ends. The sections include a first portion extending perpendicularly outwardly from the duct wall and a second portion bent rearwardly from the outer end of the first portion. When the frame is formed in this fashion, it is adapted to receive the side edges of respective arms of corner connectors whereby the ducts may be efficiently assembled by locating corner connectors in place and thereafter applying the fasteners used for maintaining the assembly.