Interesting.
My OEM headers exit pipe had a load of really tough wire mesh impregnated with some silver sealant that made the diameter of the pipe approx. 4mm wider than the Arrow TP, even the TP clamp wouldn't fit over this mesh.
Once I had prized all this stuff off - the TP was a perfect fit, but it does prevent me from putting the OEM TP back on as it will now be too big...
Either Arrow make TP's with different diameter connections (one to be used with thier headers and one to be used with the OEM headers) or Yamaha have changed the design of the OEM exit pipe...
Gonna email Arrow and ask them..