I measured my exhaust at 1.65 OD and had them widen the extension pipe to 1.7 ID. I am sure the exhaust is a metric size that is why it seems an odd size. I originally measured wrong, measured the exhaust pipe where the bracket is welded luckily they made it long and were able to cut off the wide end and re-size it for me. I think they might have been a little over 1.7 but the saddle clamp holds it well.