Yes Gekko , I think you are right , it is an M5.
And buying a saw carriage might be cheaper than making one .
I notice that one of the cross strut braces underneath has broken at the pivot bolt . Mine broke just recently , so I am going to install a cross beam like the M7 mills have .
My local aluminium supplier has 100x50 mm C section that I will use . It's not cheap tho.
I will then use the broken cross struts as braces from the cross beam to the legs .
looking forward to seeing photos of you and your mill at work ,
cheers ,
Jock