Berkey PF-2 Fluoride Filter (Set of 2) - Fits Black Berkey Purifiers Only The PF-2 is for use with Black Berkey Purifiers - If you use ceramic filters, you will need the PF-4 Primarily Filters Fluoride and Arsenic Attaches to the bottom of a Black Berkey Purifier - Used as a Post-Filter For use with Big Berkey, Travel Berkey, Berkey Light, Royal Berkey, Imperial Berkey, Crown Berkey