Mallard Armory - Hayward DEX2400Z3A Relief Valve Stem O-Ring Replacement This is the one you have been hunting for. Manufactured, tested, packaged & sold in the U.S.A. by Mallard Armory. Fits Hayward Pro Series High Rate Sand Filter Models S210SV, S244SV. Fits Hayward Super Star-Clear Cartridge Filter Models C2000, C3000, C4000, C5000. Fits Micro-Clear Vertical Grid D.E. Filter. O-Ring 3 Pack contains 2 small and 1 smaller to seal the relief valve.