The Sta-Rite 24850-0008 Filter Tank O-Ring has a 21 Inch diameter and is a replacement for the Sta-Rite S7 Series System 3 modular media cartridge filters, System 3 DE filters and System 3 sand filters with a 21 inch tank. If your Sta-Rite filter model starts with S7 this O-Ring will fit your filter.

If the O-Ring is swollen or cracked it can cause equipment to suck air and spit air back into the pool through inlets and it must be replaced. Not replacing O-rings can damage your pool equipment, have a negative effect on filtration and decrease the efficiency of pool chemicals.