Remove the old muffler. In this case a CF Muzzy that's held in at two points, the bolt on the passenger foot peg and a squeeze clamp at the mid-pipe.

Measuring for good measure. The Supertrapp aluminum racing series universal muffler has a 2" ID and a 4" exhaust OD at the diffusers. The inner core is a straight 50 MM ID, while you can see the expansion chamber shape of the muffler itself is that of a megaphone.

There's a pin that will go through the Supertrapp muffler and the mid-pipe, just as I've done on my other two bikes. See below for more.