I replace the aftermarket 4 into 1 exhaust on my '75 CB750 K5 with a MAC 4 into 2 system. The aftermarket system has flanges on the end of all of the pipes, but the ends of the new pipes have no flange and are expanded to fit over another pipe. I talked to the Honda dealer, and they tell me that there are Exhaust Flanges, that are separate pieces, that go between the head and the pipes.