Goes along with the inner flange and internal locking band (with centering extension). The outer locking band is on the surface for more help, which makes it a more powerful procedure. Contaminants of combustion usually are not trapped in the flue like it is often present in the corners of https://fireresistingductworkinsu35677.blogoxo.com/37186528/everything-about-fire-resisting-ductwork-insulation