Finally success! I went to a friend's home and he did it with me, basically, it's not the problem about insufficient force, but it's because we didn't have tool to fix the black part in place, tonight we use our foot and our body weight to fix it, and a "slight" turn make it.
Here're the results:-
A PST without all the important components, i.e. the etalon and the blocking filter:-
The etalon module:-
I was told the thread size is "M50 x 1mm ISTR", sounds good.