Can be used for fixed offsets of 15 degrees slope or in pairs for offsets adjustable from zero degrees to 30 degrees slope. Greater angles are prohibited by UL standard 103 and by the terms of the product listing. Required: Locking bands (2 packaged with each elbow kit) allow 360 degree rotation and lock the components together in place at the exact offset required. Insulated elbows can be used at the same two-inch air space clearance as chimney sections. Includes 2 elbows, 2 locking bands, an interior resupport, and couplers.