STANDARD 10" SEDIMENT FILTER CARTRIDGE: Recommend replacing every 6 months. The first stage of your RO unit is a 5-Micron Sediment Filter that traps sediment and other particulate matter like dirt, silt and rust which will affect the taste and appearance of your water. Dual density gradient sediment filter is highly recommended due to longer life and cost effectiveness. Precision manufactured from 100% pure Polypropylene fibers. The fibers have been carefully spun together to form a true gradient density from outside to inside surfaces. 9-7/8" standard size cartridge is self-sealing for a tight fit in RO units. Item 330088.