STANDARD 10" CARBON BLOCK FILTER CARTRIDGE: Recommend replacing every 6 months. The second stage of your RO unit is a 5-Micron Carbon Block Filter. 9-3/4" standard size cartridge includes rubber gaskets at both ends to ensure 100% water flow-through. Activated Carbon removes chlorine from most incoming tap water supplies for up to six months. Durable outer and core wrap keeps carbon secure throughout cartridge life. Item 330090.