Psy1280
Check the mechanical drawings, here https://astronomy-imaging-camera.com/product/zwo-efw-5-x-2″or-7-x-2″ and here https://astronomy-imaging-camera.com/product/zwo-efw-8x-1-25-inch-or-7x-36mm . Hint: they have wildly different sizes (even the boxes they come in are different).
I don't know though, if ZWO sells a 31 mm filter wheel with 7 slots. I think the 31mm one that you are thinking about has 8 slots, but it has the same outer dimension as the 7-slot 36 mm wheel and the 5-slot 2" wheel. (Only the carousels are different, from what I can tell.
Now, if you want a ZWO 2" wheel that has the same dimension as the 8-slot 31mm wheel, as I mentioned above, there is a 5-slot 2" wheel that has the same outer dimensions.
Chen
