Here is some info from page 8 of the pandora thread in the gallery, posted by Amy (girlarchitect):
I use Santa Fe Jeweler's Supply http://www.sfjssantafe.com, and have been really happy with their quick service, online ordering and online pricing. I use the#18200 silver tubing with my 3/16" mandrels it has a 5.03mm OD and a 4.3mm ID. The walls are pretty thin. If you use the size smaller, it will flare and fit the bead, but won't fit over the Pandora/Biagi bracelet end, but will fit Troll. Hope that gives everyone another option.
Another Amy (Steamer) replied that the 5mm O.D. tubing she bought did not quite fit her Pandora. So, it looks like you need this slightly larger 5.03 O.D./4.3mm I.D. size.
I've been searching the LE threads for the answer to this question, too!
If anyone has more info, please share!