Pentek WP25BB97P Big Blue String Wound Sediment Replacement Water Filter Cartridge Compatible With Culligan, Ametek, US Filter, Plymouth, Kleen Plus, American Plumber, Bruner & Many Other Brands. WP25BB97P Big Blue 25 Micron Polypropylene String Wound Sediment Water Filters. 10" long X 4 1/2" diameter. 8 per case, sold individually. #WP25BB97P WP Series cartridges are manufactured from a durable polypropylene cord that is wound around a rigid polypropylene core. They are an economical solution to reduce fine sediment, including sand, silt, rust and scale particles. WP cartridges are wound in a precise pattern around the core providing a greater filtering surface area. The result is a higher dirt loading capacity and greater efficiency than standard wound cartridges like the CW. Order a case and save even more.