These adapter rubber hose nozzles are KF-50 to rubber hose and fit a 50.8 mm or 2 inch ID rubber hose. The flange size follows ISO-KF standards and is NW-50. They are commonly used to make connections between ISO-KF fittings and rubber vacuum hoses. The ISO-KF flanges are often called quick flange fittings because they are quick to assemble. 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 contains a rubber elastomer o-ring. 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. They are made of Stainless Steel.