Is 3mm the standard width of the band on a solitaire with, let''s say, a 2.5 carat center diamond? I am just trying to figure out it out. I have never really thought about the band width before (I always look at the stones), but a friend of mine just got a 3 stone emerald cut ring and she has just gone on and on about how wide the bands are and how that is great. Could anyone clear this up for me?