Big Blue CTO Carbon Block Replacement Water Filters ( 4 ) 4.5" x 20" Cartridges 4 Big Blue Carbon Block Filters (5 micron) for a Standard Size Big Blue Housing 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. All our filters individually wrapped for freshness and protection while in shipment.