Six KleenWater AP217OR water filter housing replacement o-rings compatible with Aqua-Pure AP217. Replacement o-rings compatible with 3M Aqua-Pure Cuno model AP200. We recommend consumers keep a spare o-ring on hand to avoid urgent situations. An o-ring facilitates a water tight seal between the water filter sump and the water filter head. The most common o-rings used in water filtration are made from Buna N material. Buna N is also commonly referred to as nitrile. This is the ideal choice for cold water filtration because they are inexpensive and have superior performance characteristics. KleenWater is a trademark of Pavel Water Filtration. EnterKW217(Qty2)-RG217(Qty2) in the Amazon Search Bar to purchase a cartridge with o-ring kit.