Abstract: An injection mold comprises an outer mold structure defining an abutment surface and a core axially slidable in this structure between a molding position and a second position. The core defines a mold cavity with the outer mold structure in the molding position to mold a tubular end portion of a synthetic thermoplastic resin article therein. The core includes an annular rib defining an internal peripheral annular groove of the end portion and an end to which a mold sleeve is axially immovably connected. The mold sleeve has an end face facing and conforming to the abutment surface upon axial sliding of the core into the molding position. The mold sleeve and core end have converging confronting surfaces defining an annular gap tapering toward the core end, the annular gap defining a free end of the tubular end portion extending outwardly from an annular section thereof surrounding the groove.