Ranger rear assembly thread size

I have a hard time to confirm the specifications of the thread. Originally, I tend to think it's M77 since the objective lens cell has M77, but now I believe that it's not:

First of all, I think it's more like 3 inch rather than 76mm or 77mm:-


The hardest part is the thread pitch, if the diameter is 3", the thread pitch should also be in inch?


And here is how it looks when measured against centimeter:


This is how it looks like when unthreaded, basically, all you need to do it to slide the dovetail outward and you can see a screw directly under the dovetail, loosen it and you can unthread the rear assembly very easily.


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Two more shots: