I actually posted about this in a different thread, too:
As for the stick sizes, those terms are so broken and misleading it befuddles me. Just look at the spread in 5A diameters you have from four major stick manufacturers: Vic's are .565, Pro-Mark's are .551, Vater's are .570, and Regal Tip's are .580. Pro-Mark's 5Bs are .590- they're actually closer to a Regal Tip 5A than that same RT5A is to Pro-Mark's 5A. None of the designations are standardized, every company has their own special ones that don't make any sense, and it's all a huge cluster. The only actual order seems to be a very general one of higher numbers indicating smaller diameter, which, like... what? Even bra sizes make more sense than this stuff.