The fan is an eclipse 4" 210cfm, the 6" I initially bought was way big and pushed 630 cfm. I put a rubber gasket on the face of the fan where the tube meets and will put top and bottom latches(like tool box lever latch)to hold them together. I used heavy wire ties for now till they finish. I also plan to take the reducer off the filter and do the same for it. That will make it a single unit only 35" long.