Paul, I just had a look at mine. I have a GSO 2" 90° diagonal that I unscrewed the barrel off. I screwed the barrel from my 30mm Bintel (GSO) EP into it. They are a perfect match. I did a quick measure of both bits and they are identical.
The first picture is with the diagonal's own barrel. The second is with the one from the EP. Even the file size is the same.
