... Air Duct Material: Galvanized Steel Pipe Coupling(quick coupling,tube fittings)1. Material: Galvanized Steel Panel, Stainless steel sheet is available2 ... :It used to connect the end of duct, and has exactly pathway and easy toconstruction.3. Inner Dia.100,150,200,250 ... ,320,400,500,630,800 and so on. Pipe Coupling(quick coupling,tube fittings)