Replacement O-Ring for S400 Compressor outlet flanges. Used with the following WCFab products: LB7 Duramax S400 Single Turbo Install Kit (WCF100489), 2004.5-2007 5.9L Cummins S400 High Mount 2nd Gen Swap Kit (WCF100486), 2003-2007 5.9L Cummins S400/Stock Twin Turbo Kit (WCF100567), 2003-2007 5.9L Cummins S400/S400 Side by Side Compound (Twin) Turbo Kit (WCF100580)