Our KF40 NW Thick Wall Stainless Steel Bellows Flexible Hose follow ISO-KF standards. The Wall thickness = 0.25mm. They are commonly used to build vacuum systems with a vacuum level < 10E-8 mbar/Torr. 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. The centering ring contains a rubber elastomer o-ring. The standard sizes for quick flange fittings are KF10, KF16, KF25, KF40, and KF50 with flange sizes NW10, NW16, NW25, NW40, and NW50, respectively. They are made of corrosive resistant 304L stainless steel and have a thick wall, ideal for vibration absorbtion and mis-alignment.