No idea sorry Houghy, but I do have a Question regarding the item though. What are these used for primarily, is it to stop unwanted dust ect... reaching your EP or Camera?
Just a "normal" 2" filter thread Hough?
If so I probably have one, or can get one or two for you. So can you, all you need is an "older" camera store, one which used to sell "real" cameras. The 48mm filter size that was a Canon standard for many years is the same. I actually use a red, and an orrange 48mm filter on the Denkmeir OCS (this is 2"), while bino-viewing the lunar surface, cuts down the bright glare.
Gary