Pandora and Troll - are the charms interchangeable?

[TracyK]

My friend has a pandora bracelet - and we were chatting and neither of us knew if you could buy - say - a troll bead charm and use it on her Pandora bracelet?

I think they say that they are not interchangeable, however I think pandora beads would fit on a troll but not the other way around. The only problem is they are very different style wise iyswim.