The 100312705 Centering Ring Assembly is designed for NW40 size ISO-KF vacuum flanges and features a Viton® O-ring and 304 stainless steel construction. Centering rings are inserted between two same size ISO-KF flange faces to provide the vacuum seal when joining them. The included Viton O-ring is recommended when high temperature, chemical resistance or long installed life make them beneficial. Series 31 ISO-KF vacuum components are designed for use at subatmospheric pressure and use standard interface dimensions defined by the International Standards Organization (ISO) allowing them to be interchangeable with other ISO-KF compliant components.