KDF/Catalytic Carbon Pre-Filter reduces Iron, sulfur, chlorine, chloramines and heavy metals. The pre-filters doubles the filter life. Great for city or well water! Bacteriostatic qualities do not allow microbes to breed in filter. #728772 is 20 x 2.5 inches. #741630 is 12 x 2 inches. #741640 is 10 x 4.5 inches.