Watts SF5-20-425, Pentek WP5BB20P, WP5BB20P Compatible String Wound Water Filter Cartridges, 4.5 X 20 Inch, 5 Micron Replacement Water Filters (3) - with WS03X10039 O-Ring (1) Three KleenWater 4.5 x 20 inch String Wound Filters - One KleenWater o-ring 5 micron dirt, rust, sediment entrapment Made of FDA grade polypropylene - Made in the USA Precise geometric patterns insure high efficiency O-Ring is compatible with Pentek, Culligan and Pentair "Big Blue"