Air Box 1, Stealth Edition (4'')The Airbox 1 carbon filter has 4" flanges and a CFM of 500. These units are completely airtight and easy to install, use, and maintain as they fit into any ducting or filtering system. Made with 100% premium virgin coconut charcoal, they feature replaceable high flow filters which use 100% of the available surface area, for optimum performance. Great for commercial or residential use. (1) pre filter included. Made in the USA.