body sealing surface 46 and body retention surface 48 adaptor 20 includes external annular sealing groove 24 which is defined by adaptor sealing surface 50 and adaptor retention surface 52 sealing surfaces 46 and 50 each lie in a plane generally perpendicular to the longitudinal axis 9 of the coupling and oppose each other in substantially parallel and spaced relationship body retention surface 48 is of cylindrical shape facing inwardly from the lower most projection of the body structure while adaptor retention surface 52 is cylindrical in shape facing outwardly from the uppermost portion of the adaptor structure when leading end 26 of adaptor 20 is inserted into channel 16 of body 14 these four sealing and adaptor surfaces 46 48 50 and 52 form a washer seal cavity in which washer 30 is positioned and retained upon assembly the cavity is generally annular in shape and may be substantially square or rectangular in cross section in the assembly of u s pat no 5 131 695 the stop surface element of such assembly does not contact the adaptor until after the maximum intended compression of the washer has been exceeded in the assembly of the instant application by comparison the stop surface contacts the adaptor substantially prior to the time the maximum intended compression of the washer has been exceeded in.