Exhaust Band Clamps

I'd assume those were for butt joints. ***-U-ME! How do they compress a round pipe (with no slits in it). If it were a butt-fit, the clamp would seal both OD's and then become the seal in the middle. Do they sell these as stepped for different pipe OD's? I would not expect to slit a new pipe for these to work.....but if they are working in your application...moot point.