Rugged, heavy wall head for use with 6384, 6386, 6388, 6423, 6425, 6427, or 6429 reaction flasks. Duran flange supplied with a shallow O-Ring groove for use with mating grooved flask. #15 Ace-Thred center and various #15 and #7 side necks available allow connections under pressure conditions without danger of blowout. For connectors, see 5844; for bushings, 7506; for plugs, 5846; for clamp, 6517.