Berkey BB9-2 Replacement Black Purification Elements, 4-Pack Includes: Four Black Berkey Replacement Filters (BB9) Each Filter is 9 high. Cleanable, Self-Sterilizing Filters Each (1) Black Berkey Filter has a life span of 3,000 gallons that's 6,000 for a 2, or 12,000 for 4 Will fit the following Berkey Systems: Travel, Big, Royal, Imperial, Crown and Light. BB9s fit most gravity water filters, so other gravity systems can easily be upgraded to a purifier.