These KF-40 Centering Ring Restrictor vacuum fittings follow ISO-KF standards and have a flange size of NW-40. They are used to fully or partially impede the flow of vacuum, allowing for greater control of process applications. A circumferential clamp and centering ring form the vacuum seal between the connecting flanges (please see top right figure - click to enlarge). The centering ring restrictor contains a rubber elastomer o-ring, either Buna or Viton. The standard sizes for quick flange fittings are KF-10, KF-16, KF-25, KF-40, and KF-50 with flange sizes NW-10, NW-16, NW-25, NW-40, and NW-50, respectively. These fittings are made of corrosive resistant Stainless Steel with a Viton O-Ring.