I have the original Drummer w/alloy end-cap on my Ulysses and the stainless version on my XB12 lightning.. the OD is 2.5" and the ID is 2.25" on both
I'm not sure if those diameters are 12 specific, but something tells me they are from a tuning standpoint as Kevin wanted to know if I had a 12 or 9s before the SS version build