It is hard to imagine others haven't encountered the same problem. Clearly, the designer was aware of the issue, or else there wouldn't be holes for a tool. It is unfortunate that a removal tool isn't supplied by ZWO with each electronic filter wheel. I'm still stuck, or should I say, the adapter is still stuck.
If you still can't unscrew it, you could return it for fix. But it pays a lot.
There is one way we can help you, that is return it back, then we can fix it. But this way will cost a lot.
Shipping back to ZWO is not a helpful solution. It would be cheaper to remove the T2-T2 adapter destructively by grabbing the exposed threads in a vice, and purchasing another T2-T2 adapter which is a $12 part if I recall. Unfortunately, I could still run into the same problem again in the future. Clearly the engineer who drew up the part was aware that it could get stuck, because s/he put the pair of holes in the part. My opinion is that it would be appropriate to include a removal tool with every motorized EFW and any other ZWO device which can suffer the same problem.
I spoke with a friend who works in a metal shop. He recognized the name of the tool that I want as an adjustable pin spanner. The tool is most often used in angle grinders, and it is often used to tighten/loosen retaining disks in the bicycle world. At the very least, ZWO should be advising its customers of the tool needed. ZWO support confirms that the pin holes in the T2-T2 adapter are 3mm. I have ordered a Park Tools SPA-1 adjustable pin spanner with 2.9mm holes from Amazon.
https://www.amazon.com/Park-Tool-SPA-1- ... 107&sr=8-1
I shouldn't have to purchase a 3rd party tool. I suggest that ZWO start including a fixed pin spanner matched to the pin holes of the T2-T2 adapter. It would not be an expensive part.
And we are glad that you have solved the problem. Also we will consider your suggestion.