peripheral surfaces terminate short of the free ends 7 7a of the male members and the corresponding inner ends of the surfaces 6 6a of the female member and when the members are fully engaged together a generally axially directed surface on the free end of each male member is brought into sealing abutment with a corresponding oppositely generally axially directed surface on a shoulder 8 of the female member as will be described more fully in relation to fig2 to 5 which show only the free end 7 of male member 1 and the corresponding portion of shoulder 8 and the adjacent internal surface of the female member 2 as shown in fig2 the free end 7 of the male member 1 is provided with a first radially outwardly and axially directed annular surface portion 9 which has a radius of curvature r1 and a second radially inwardly and axially directed annular surface portion 10 having a radius of curvature r2 the surface portions 9 10 are interconnected by a third annular surface portion 11 having a radius of curvature r3 which surface portion 11 merges with surface portions 9 and 10 at lines 12 and 13 where the adjacent surface portions have common tangents to remove any discontinuity in the curvature of the surface portions 9 10 11 the third surface.