Abstract: This invention is directed to an internal expansion coupling system offering improved thrust restraint when joined to a pair of tubular members, preferably plastic, aligned in end-to-end relationship. The system comprises an elongated open ended tubular joint member formed from at least one, relatively rigid, rectangular sheet-like member, where each sheet-like member is defined by a pair of opposing sheet ends and a pair of opposing sheet sides, and a pair of sheet ends overlap such that the end portions thereof lie in close proximity to each other. The joint member is provided with a continuous circumferential gasket sealing sleeve formed of an elastomeric material and overlapping each said sheet side about the open end of the tubular joint member, where said gasket sealing sleeve is adapted to lie adjacent to and be compressed against the inside wall of said tubular member. Further, a member accessible externally thereof, as known in the art, is provided for expanding the tubular joint member.