I just ordered new baffles today for my HB X-bow. I took those big honkin' baffles out and measured the OD at 2.6". I spoke with Jim, at BCT, and he said they are probably listed as 2 5/8". That's about what I measured on the pipe ID with a borescope.
I ordered the QBL-2125 model, which is the Thunder MOnster QQ. It is only 2.125" in diameter, but Jim said that was okay, as some of their baffles don't have to fit the full pipe ID.
It will be a seriously radical change from the baffles in the X-bow. They were 18" long, very restrictive, and making my bike run rich, judging from all the soot built up inside. The new ones will unleash both sound and power, I'm guessing.
Hope this helps,