Goes along with the inner flange and inner locking band (with centering extension). The outer locking band is on the outside for more help, which makes it a more robust process. Reduction in cross-portion: The inner Proportions (width and height for rectangular ducts, diameter for round ducts) in the smoke https://fire-resisting-ductwork-i56677.blue-blogs.com/44418611/top-grease-tight-extract-ductwork-secrets