The OR-033 O-Ring is the brine ring o-ring for the Pentek RO-3500/American Plumber WRO-3500 RO System, and the Pentek RO-3000/American Plumber WRO-3000 Reverse Osmosis Systems. The OR-033 rubber o-ring gasket is made of FDA Approved EPDM (ethylene propylene diene monomer) Rubber. The OR-033 o-ring should be replaced if there is damage to it. The Pentek/American Plumber OR-033 is also known as part number SH143438. The Pentek OR-033 Brine Ring O-Ring is different from the larger membrane housing O-Ring OR-233.