I think its totally a personal preference. I have seen a lot of people stack the 10mm bracelets and 7mm, they are meant to be worn stacked or alone, which ever you prefer! I personally prefer the same style when stacked togather like 3 bracelets with gemstone tips... I think it just looks a little more uniform that way. For example, a pearl tip, blue topaz tip and amethyst tip would look amazing together in any size...It also depends on your body size, wrist size and personal style...