There are mainly two kinds of air ductwork flange systems of duct connection: American standard and European standard, which is the TDC/TDF flange, recommended by SMACNA association and LT/T. TDF unit is one of the two universal flanges making systems in the world, TDC and TDF rectangular duct flange, with low cost, well-seal and easy-fabrication, specially suitable to produce a duct with medium section area and applied in large-scale industrial manufacture. As a flexible machine, TDF will adapt to an auto line with a Pittsburgh lock machine, notcher and bending machine. It may also be used on site.