Big Blue (GAC) Granular Activated Carbon Water Filters 4 pcs 4.5" x 20" Cartridges Replacement filters for Amazon item B01AR1SE7M or any standard size 20" Big Blue Housing 4 Big Blue Granular Activated Carbon Filters. Standard size filters 4.5x 20 These can used for residential and commercial applications. Effectively eliminates many impurities from tap water to offer sparkling clean and great tasting water throughout your whole house.