The CF (ConFlat) flange is the most widely used for high vacuum and UHV applications. Many gauges, instruments, accessories and feedthroughs are available on this flange system.
The seal mechanism is a knife-edge that is machined below flange's flat surface. As the bolts of a flange-pair are tightened, the knife edges make annular grooves on each side of a soft metal gasket. The extruded metal fills all the machining marks and surface defects in the flange, yielding a leak-tight seal. The CF seal operates from 760 torr (1013 mbar) to-13 torr (-13 mbar), and within the temperature range -196° C to 450° C (depending on material). Flange sizes in North America are determined by outside diameter (O.D.). In Europe and much of Asia, the internal diameter (I.D.)—actually the nominal I.D. of the largest tube that can be welded to a bored flange—is used.