A coupling for use in joining together a ductile iron pipe and a plastic pipe includes a ductile portion, a plastic portion and a transition portion that has a frustoconical transition inside surface. The ductile portion has a first end that is adapted to accept the ductile iron pipe, an annular groove adjacent to the first end that is adapted to receive a sealing gasket, and a ductile engagement portion having an inside diameter that is sized so as to form a friction fit with the outside diameter of the ductile iron pipe. The plastic portion has a second end that is adapted to accept the plastic pipe, an annular groove adjacent to the second end that is adapted to receive a sealing gasket, and a plastic engagement portion having an inside diameter that is sized so as to form a friction fit with the outside diameter of the plastic pipe.