The CF flange is the most widely used for HV 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 the 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 from103 mbar to < 1.3 x 10-13 mbar, and within the temperature range -196° C to 450° C (depending on material). Flange sizes in Asia, the nominal internal diameter (nominal I.D.) of the largest tube that can be welded to a bored flange is usually referenced in their nomenclature.