Heads with four necks, three inline standard taper joints and one perpendicular #7 Ace-Thred™ thermometer joint. Included 5029 nylon bushing & FETFE o-ring permits vertical adjustment of 6-7mm OD thermometers. Use with our 6504,6511 & 6516 reaction vessels that feature either a 137 x 100mm ID or 168 x 130mm ID flat flange. Use with our 6508 or 6510 clamps. For improved sealing of flat ground flanges, please see our 6495 product family of gaskets. Note: vessels with o-ring grooves seal with the vessel's supplied o-ring.