The CF Flange system is illustrated below.
Each flange face is identical and contains a knife edge. When bolts tighten these flanges together with a copper gasket between them, the knife edge is forced into the copper. This action generates an annular groove in the gasket capable of withstanding high pressure and temperature, fills all voids and defects and produces an extremely reliable leak tight seal. Suitable for all vacuum applications, CF flanges are especially suited to conditions requiring ultra-high vacuum, very clean environments, high temperatures or the containment of toxic, corrosive or radioactive materials.