Or I can just measure them...
Just as an example.. I have some Tibetan shos and skars, some of them are 29¼ mm .. They certainly don't fit US Small Dollar holders and if I put em in US Large Dollar holders, they'll be 1 cm loose!
Another easy example are the old canadian 5 cents. They are 15.5 mm in diameter... They would better be in 17.5 mm with 2 mm spacing than in 20 mm (1 cent) where they would be like almost the third of the coin loose...
But well, this is just my opinion... I think a collection in holders would look better if the window of the holders were not more than 2 mm larger than the coins. Pure aesthetical matters, I agree...
Max