These KF-40 vacuum fitting BUNA O-ring replacements are designed for ISO-KF standards with a size of NW-40. They are commonly used to build foreline vacuum plumbing and process systems. They 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 BUNA. Description: Standard Nitrile is also known as Buna-N. Excellent resistance to petroleum-based oils and fuels, water and alcohols. Nitrile also has good resistance to acids and bases, except those with a strong oxidizing effect. Limitations: Avoid highly polar solvents (Acetone, MEK, etc.) and direct exposure to ozone and sunlight. Temperature Range: –55° to 120°C (–65° to 248°F)