Rainsoft COMP-P-12 Hydrefiner Compatible Replacement Water Filter Cartridge The Rainsoft P-12 Hydrefiner Compatible Replacement Filter offers carbon block filtration for excellent The RainSoft Hydrefiner Compatible P-12 Filter Cartridge fits Hydrefiner Model numbers 9875&#44; 9878&#44; The Rainsoft P12 filter cartridge features 1/2 FPT Screw On Cap. The Rainsoft P-12 compatible water filter provides contaminant reduction for: sediment&#44; chlorine Cartridge Size: 4-9/16 Diameter x 6 Long.