Plastic coating thread and coupling assembly

A coupling assembly comprising an annular coupling having internal threads having a central portion having a plastic corrosion-resistant coating and opposed tubes having a continuous plastic, corrosion-resistant coating and having external threads inserted into said coupling with said internal threads, including said central portion thereof, and said external threads being in threaded engagement to produce a seal and a corrosion barrier at said central portion of said annular coupling, an annular gasket of rigid material mounted between and in sealing engagement with opposed ends of said tubes within said coupling, said gasket having a continuous radial portion extending between said opposed ends of said tubes and spaced apart from each said opposed ends of said tubes a distance sufficient to receive a plurality of O-rings mounted between each said tubing opposed ends and said continuous radial portion of said gasket and in sealing engagement with each said plurality of O-rings, a pair of opposed flanges extending from opposite sides of said continuous radial portion of said gasket and into sealing contact with an interior surface portion of said tubes extending from each said opposed end of said tubes.