Big blue filter set for 3 stage units includes 3 filters in this pack of 3 filter set. Fits standard whole house filter units, interchangeble with any similar filter cartridge. Standard Size replacement set fits 20"x 4.5" for Triple Big Blue Housing This micro straining of the water will provide clean and clear drinking water. Stage 1: 4.5" x 20" poly spun sediment filter for dirt, rust, sand Stage 2: 4.5" x 20" GAC carbon filter for chloramines and chlorine removal Stage 3: 4.5" x 20" carbon block filter for all other chemicals, odors, pesticides