Permanently replaces traditional rubber washers. Guaranteed for life to never wear out. Uses a faucet"s own internal water pressure to stop leak and create a watertight seal. Seals on the interior of faucet"s seat and never makes contact with a sharp meta l surface. Seals on chipped or worn seats. Exceeds ASME and CSA standards and is NSF compliant. Two-pack contains two DripStop valves. DSV-A - Fits American Brass, Harcraft, Price Pfister, and Savoy faucets. DSV-B - Fits American Kitchen, American Standa rd, Arrowhead Brass, Barnes/Western, Central Brass, Eljer, Indiana Brass, Kohler, Phoenix, Repcal, Royal Brass, Sayco, Sterling, Streamway, and Union Brass faucets. DSV-C - Fits B & K, Burlington Brass, Crane, Gerber, Milwaukee, and Univers