Hard to tell, but it looks like a m42x1mm thread on the back... (looks too course to me for a T2 or M42x.75)
A few questions...
1. Does the rear thread measure 42mm?
2. Does this thread on the back unscrew, revealing a finer M42x0.75 thread?
3. Does the focus control go past the infinity mark?
Being a mirror lens and if the thread is for direct connection to a camera, the problems are going to be :-
1. Getting focus with a star diagonal attached.
2. Adapting (if its a M42x1mm thread) with the even shorter backfocus.
You can get adaptors (for either thread) to 1.25" that will focus "straight through", but unless it focuses past the infinity mark it will be difficult to use a 1.25" star diagonal.
One possibility would be to use a Barlow modified to fit inside the diagonal nosepiece, but this has the disadvantage of increasing the focal ratio. (which can be handy for the Moon/Planets, but not so good for wide field)
Another possibility is that a 0.965" diagonal has less backfocus and might come to focus without modification.
If you have diagonals and eyepieces to try out, then best bet is to simply offer them up to the back and see what focuses and what doesn't.
Edit: - I've just seen some pictures of them online and read a post above - It appears they did come with a diagonal and eyepieces - so the chances it will focus are looking good!
I adapted my Vivitar 500mm F8 mirror lens, (62mm aperture) to make a miniature ultra portable scope :-
This is a T2 mount designed to couple directly to a camera via T adapter. The backfocus was therefore very limited. To get it to focus I had to modify both the diagonal and the mirror lens.
The diagonal had the nosepiece removed and a T2 to M39mm stepping ring was 'melted' into the plastic housing. Also note I used a Prism diagonal, as the backfocus required is less than a mirror type.
I then had to modify the focus assembly (by filing away some metal) to allow the focus to go past infinity (i.e. screw in further).
Edited by andycknight, 22 May 2019 - 01:21 PM.