Use for offsets around obstructions such as rafters, ridgepoles, or joists. May have one pairs of elbows if needed. Offsets greater than 30° are not permitted in accordance to UL 103 standards. Large diameters are restricted to one pair of elbows. Available in galvalume (GA) and stainless steel (SS) outer wall and stainless steel inner wall. Fasten with screws.