Honeywell HRF-AP1 Universal Carbon Pre-Filter HRF-AP1: * Contains 1 filter that should be replaced every 3 months * The perforated design makes 1-8 pre-filters depending on the air purifier model * Helps reduce odors and maximize filter life * Works with all Honeywell True HEPA Air Purifiers including: 10500 series, 10590 series, 11150 series, 12500 series, 13300 series, 13503, 13520 series, 13530 series, 14500 series, 17000 series, 18100 series, 40000 series, 50100 series, 50150 series, 50200 series, 50250 series, and 50300 series models