Goes along with the inner flange and interior locking band (with centering extension). The outer locking band is on the outside For additional assist, rendering it a stronger technique. Contaminants of combustion usually are not trapped in the flue like it is usually located in the corners of an oblong https://grease-tight-extract-duct01223.aboutyoublog.com/43333839/getting-my-grease-tight-extract-ductwork-to-work