These ISO DN 80 centering rings are made of PTFE with Viton® (FPM) rubber O-rings and are used to seal both ISO-K and ISO-F vacuum flanges. The centering ring forms the vacuum seal between the two mating ISO-K or ISO-F flange faces. ISO-K fittings are quick to assemble using claw clamps and can be connected together in any orientation. The claw clamp hooks into a ridged groove in the back side of the ISO-K flange. ISO-F fixed flange vacuum fittings have a bolt circle where bolts align the two flanges. These ISO 80 centering rings are commonly used to build process vacuum plumbing and systems for industrial and high vacuum applications.