danoglide65 It came with the camera for use of the fish eye camera.
Yep; that's similar but may not match the filter thread. Notice that the thread for a C-mount camera lens is different from that of a 1.25" filter thread -- if I recall, C mount lenses are based on Imperial units 1"/32 tpi (approximately 25.4mm with 0.79mm pitch), while the 1.25" filters are based on Metric units 28.5mm/0.6mm pitch. Close, but no cigar.
The link I gave is for a T2 to 1.25" filter (I use a couple for my guide scopes to attach 1.25" filters to the ZWO pancake cameras).
Depending on how old that adapter is, you may also have to tape off the holes.
Notice in the picture from my link that the holes go all the way through and will cause really bad light leaks. You need to tape them off with electrical tape to avoid light leak. The image is probably from a ZWO documentation from a couple of years ago.
ZWO has since learned the lesson (obvious to us, but not to them, I guess) and the holes in the current versions are now countersunk (two from one surface and the other two from the other surface) instead of going all the way through. Be sure to check.
Use a "lens spanner" to install and remove the adapter. It is worth getting one if you don't already have one since they will be useful for removing the "zero optical length" male-to-male tube adapters too. And also to remove glass filters from their holders.
Chen
