The H603-M is the original manufacturer’s replacement final stage square HEPA filter for Abatement Technologies, Inc.’s (Old) CAP600 (fits S/N's 0 - 5,000 & 60,000 – 61,000, manufactured before 06/02/98) Central Air Purification system.
The H610C-99 is the original Manufacturer’s replacement final stage round HEPA filter for Abatement Technologies (New) CAP600 (fits units S/N's 5,001 - 59,999, manufactured after 06/02/98) and all CAP1200 Central Air Purification systems.