On duct lengths Air-Flow should always be from Big End to Small End. Butt-Weld Construction Continously welded two sections together. For field adjustment, the other end is a loose flange. However, duct joints can be furnished with rings continuously welded on both ends if desired. We recommend welding rings on both ends of material 12 gauge and heavier.
Final seal is accomplished by caulking in field.
Van-Stone is to turn an edge which will retain rings and permit the ring to be rotated as necessary to match bolt holes.