There are mainly two kinds of flange systems of duct connection: American standard and European standard, which is the TDC/TDF flange, recommended by SMACNA association and LT/T mate flange as well as improved GDF/PDF flange recommended by UK HVAC association. TDF unit is one of the two universal flange making systems in the world, 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.