I had the same experience. I've been frustrated that the internal measurements of this and other products don't seem to reflect reality. Like the 1.5 mm cord. I tried this one on a 1.5 mm chain and it wouldn't fit eather.
Good but not what I needed
The quality of the end cap is great - it's very dainty and small. I bought these, thinking 2m would accommodate my 1.5m leather cord, but the cord doesn't fit at all ... however this is probably my fault as I don't have any experience with leather and cord end caps, so maybe I needed to allow more room.
However there doesn't seem to be a bigger cord end cap at Artbeads that might fit the 2m leather cord they sell ... maybe a link from one to the other (i.e. this cord end would fit this particular leather cord, etc) would be really helpful!