Mallard Armory - Hayward CX900F Filter Head O-Ring for Hayward Star-Clear Plus cartridge filter models C751, C900, C1200, C17502 This is the one you have been hunting for. Manufactured, tested, packaged & sold in the U.S.A. by Mallard Armory. Mallard Armory seals are high-grade synthetic rubber O-rings to replace old, worn, or cracked o-rings to provide a proper seal for your pool system As shown in diagram, this o-ring fits into a groove on the outside of the filter head and seals between the filter head and body Compatible with C1200, C12002, C12002S [C12002(S)], C1502, C17502, C17502S [C17502(S)], C2002, C751, C7512, C900, C9002, C9002S [C9002(S)] One o-ring doubled over in bag