MILLIARD 6&rdquo;x20&rdquo; Carbon Filter Multi-purpose. Use it with any 6 fitted air duct system. Great for home & garden use. Designed for use in the MILLIARD Hydroponic Grow Tent with the MILLIARD 6 air duct and MILLIARD 6 Inline Blower Fan. Clear the air with 20 of extended air-scrubbing surface area to remove odors and contaminants. Felt pre-filter is reversible for extended longevity. Filter measures 20 long and uses 6 diameter duct fitments.