I have just measured mine the pipe is 40mm outside diameter, with the collar welded on it's 44mm internal diameter at this point is 29mm/30mm. Hope this helps.Hi, really interesting to read about your project, Im also working on a 750 and Im wondering if you could help me by meassuring the ends of the exhausts, the diameter and length of the small pipes welded on the ends that goes into the top? Charlie