man, that's some ugly welding! oh, wait, I did that!
Without referring to my notes, I believe I used a 5/16 bit to make the hole, then used the corresponding size bolt to attach through that tube.
Doing it over, I'd use some bearings for a tighter fit.
If you're talking about the fork tubes attaching to the "box", that is just welded. HOWEVER, someone recently gave me an improvment on that, which was to use the hole saw to cut holes in the flat stock and run the fork tubes through that hole.