Installed mine. Sits nicely horizontal, is not tilted and got it for 236+ shipping.
This has 3" OD, the ID is roughly 2.75-2.8", except the pipe that goes into the axleback is 3" ID (that's rare).
However, the axleback tip has a cone that is welded into the muffler can and that cone necks inside the can to lower than 2.75", I'd say 2.65-2.7".
An axleback that is completely 3" inner diameter would flow more, but would be louder.
I wish they trimmed that cone to where it was at 2.75" ID, to have everything even, but maybe it was too loud that way.