O RINGS

O Rings are sized according to the filter canister size.  Canisters for the most part come in three sizes.  SlimLine, Regular and Big Blue (Heavy Duty).  These three sizes apply across the board to Pentek, American Plumber, Ametek, US Filter and WaterSafe.  OMNI FILTER has a variety of sizes that are generally identified by the name of the system that is installed.  Companies that sell proprietary systems have their own special O Rings which in some cases use one of the standard sizes but generally are only available from the manufacture.