Hose clamps work great on sections with straight joins. If you cut through the radius of a 45 or 90 where the mandrel bend necks, you will see hose clamps do not work. When the diameters do not match the hose clamp does not grip both pieces. It grips the piece with the largest diameter. Best practice is to avoid cutting on the bend, but sometimes it is unavoidable for complex systems. Headers that fit in cars with little under-bonnet room have to snake down past a firewall, over a CV shaft and up under a car body, which happens to have a tunnel offset slightly from the exhaust ports makes it nigh on impossible to not cut on the bends to get the right fit..