Is that missing an oring?
Easy, UFS parts. UFS is larger than 23mm so nothing else!
Here is one for you guys. I got the piece on the left from a guy with an iAtty I purchased. He didn't know what is was and I certainly dont. The piece on the right is an Ithaka clear window for size comparison. The OD of the piece in question is 24.5mm if that helps.
I am not even sure its a GG item, but just looking at the quality of the threads I think it might be.