Reaction Vessel Lid, 3-Neck, 45/50 Center Neck, 2-45/50 Side Necks, 200mm Schott Flange. Three neck vessel lid to fit CG-1920 through CG-1936 vessels. Lid has a flat ground surface allowing it to be greased or used with an o-ring. NOTE: Three neck lids are available with joint sizes and configurations other than those listed, please call for details.