These Aluminum KF-25 Bulkhead Clamps are commonly used to build foreline vacuum plumbing and process systems. Adapts to a baseplate or fixed flange. Uses standard KF seal assembly. Comes with 6 stainless steel 10-32 X 5/8 inch bolts and 6 washers. 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 ALUMINUM.