This was really interesting and useful.
When I upgraded my refractor with 2.5" flatfield flattener and later a 3" I had big problems until I got the right parts.
You can read here what threads I had to use.
2.5" ff + reducer:
http://astrofriend.eu/astronomy/proj...refractor.html
and
For the 3" ff:
http://astrofriend.eu/astronomy/proj...flattener.html
I will later upgrade the 3" ff with an off-axis adapter, then it starts all over again to find correct parts, not only the threads, they must be of the correct lenght also.
Maybe I shall collect all threads in a table later?
ps.
I think I have a 1/2" bolt to my EQ6 Synscan Pro mount, not M12, at least I bought a 1/2" recently. I will check it up later.
/Lars