Flange is formed with a groove in the flat portion of the mating surface to accept an O-Ring. The flange also has a ground surface, permitting assembly with either the CG-148 flat flange or CG-149 lid blank using grease. In the greased application, the O-Ring groove prevents grease from entering the reaction kettle and causing possible contamination. Outer taper of flange is formed at a 45° angle to accept the CG-141 clamp.