Abstract: A coupling device for joining ends of pipes together or capping an end of a single pipe. The device includes a metal insert having serrations for engaging an inner surface of a plastic pipe, a deformable coupling member which overlies the pipe and a metal ring of smaller inner diameter than the outer diameter of the coupling member for compressing the coupling member and plastic pipe against the metal insert. A space forming feature reduces the insertion force required to slide the metal ring over the coupling member. For instance, the metal insert can include a circumferentially extending groove on an outer surface to accommodate flow of the plastic pipe as it is deformed by the metal ring. Alternatively, the coupling member can include a recess, groove or projection, the inner surface of the coupling member can be tapered, the end of the plastic pipe can be tapered or a compressible member or a ball bearing can be inserted between the end of the pipe and the coupling member to accomplish the same result.