Abstract: An improved open ended frusto conical sleeve member suitable for use as a sealing interface between the co-operating mating surfaces of a tapered male/female push fit type glassware joint is disclosed. The sleeve member, which has a wall thickness of less than 1.5 mm includes at least two integral, generally circumferential ribs and an external annular flange for gripping during assembly and disassembly of a joint incorporating the sleeve member. The sleeve member, the ribs and the annular flange are constructed from a material having a static coefficient of friction of less than 0.2, a hardness of from 50 to 80 on the Shore D scale, and which is resistant to thermal degradation up to 200.degree.C and to structural degradation when immersed in a corrosive chemical for 12 hours at 50.degree.C.