The Dunhill Group sizes always make me smile. There may be actual standards for these somewhere, although I believe they might be pretty shaky with so many different chamber configurations. It would take someone adept at calculus to categorize every pipe to standards. I joke that the Group sizing system was designed to frustrate engineers and other technicians who like quantitative data that makes sense. Whereas, if you are a non-techie and just learn how various pipes are sized, after you own a few, you can somewhat get it right by intuition. I think it is or was Iwan Ries who noted Group size on their online inventory, and that gave me a pretty good feel for it after a while. And it was a "feel," and not a precise measure. For this survey, I say a bowl is a bowl. Whether it's Brad with his megapipes or members sipping flake in their Group Ones.