Though, on first blush, the Peterson shape number system can seem enigmatic, it really is pretty organized and logical. In this regard the "B" series sits a bit outside the fence. Generally they are larger than Peterson's standard shapes and yet a tad smaller than most XL designations. In addition, if a shape seems like it would be out of place within the English standard chart, there's a good chance that the model will have a "B" in front of it. This straight sitter Rhodesian (the 'B2' shape) is a perfect example of that, meeting both criteria.
-- Sykes Wilford