Attaches to central vacuums and filters the dust out of the exhaust, but is NOT TO BE USED with filter-less systems, only with bag or filtered systems. There is too much dust coming out of cyclonic systems and it will clog the filter and damage the motor. The Centra Exhaust Filter attaches TIGHTLY to a central vacuum fitting such as a coupling or 90-degree elbow (something with 2-3/16 inch outer diameter). Overall dimensions are 11.5" long, 4.5" wide, and 4.5" tall (tapering down to the other end). Change the Centra Exhaust Filter about every third emptying of the cycle, or when it gets darkly discolored. Enjoy a healthier environment today with the Centra Exhaust Filter! Filters down to 1 micron size!