Features: 1) Can be used for fixed offsets of 30 degrees slope 2) Greater angles are prohibited by UL standard 103 and by the terms of the product listing 3) A locking band is required to join the elbows, which allows 360 degree rotation and lock the components together in place at the exact offset required 4) Can be used at the same two-inch air space clearance as chimney sections 5) Requires 2 for each offset