Spun polypropylene nominal 1 micron sediment reduction filter for 10 inch filter housings. This is commonly stage 1 of your system. Also included the 1 micron extruded Carbon block. Fits all standard 10 inch housings. Used for removal of chlorine, VOCs and more. This is commonly the second stage of an RO system. This filter is rated at 1 micron nominal. Sediment filters and Carbon Block filters are best changed every six months. These filters will change color quickly, this does not indicate exhaustion of the filter. Exhaustion of the filter is usually accompanied by pressure loss to the system. This product contains (2) solid carbon block filters and (2) poly sediment filters!