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