Yeah, just need to loosen this set screw closest to the collar...
Yeah, actually 19mm... Ignore my cheapy calipers, kinda sentimental as I have had them for over 25 years and never saw a reason to "upgrade":
Those calipers are LEGIT. And I would trust them as much as my new harbor freight ones .
I just want to add, cuz I thought it was funny, Astromania pointed me to a different vendor for what they thought would be the right scope (nice of them, and they were correct), and Celestron support said, "I do not think I have ever seen this version of the CG4" (but after providing them measurements from my mount, they also confirmed the 94223 would fit).
Got the 94223 in yesterday and it screwed right in. It does fit the older CG-4 mounts as long as you unscrew the original polar alignment scope fitting. I need to post an answer on amazon to correct the person who said it wouldn't/didn't.
Thanks for the help everyone!!