The 100312505 Centering Ring Assembly is designed for NW40 size ISO-KF vacuum flanges and features a Buna-N O-ring and aluminum construction. Centering rings are inserted between two same size ISO-KF flange faces to provide the vacuum seal when joining them. The included Buna-N O-Ring is recommended for moderate temperatures and when installed useful life is consistent with the Buna-N material. Series 31 ISO-KF vacuum components are designed for use at sub atmospheric pressure and use standard interface dimensions defined by the International Standards Organization (ISO) allowing them to be interchangeable with other ISO-KF compliant components.