A 1 oz silver Canadian Maple is 38 mm in diameter, so you might think that a plastic coin capsule with an inner diameter of 38 mm would be the perfect fit. Right? Wrong. It might work for other coins, but for the 1 oz Canadian Maple, the fit is so tight that the case cracks when you put the lid on.
So I got a 39 mm capsule and it works, though there is a little space around the sides of the coin.