I think it was Superlift that I bought the u-joint kit for when I swapped in the 60 that came with studs. They had the 5/8" course thread to go into the housing on one end, then the fine thread (same as the u-bolts) on the other end. The first problem was that they were way too long.....mainly that the unthreaded center section was too long and you couldn't get the top nuts tightened down. I guess the Superlift springs are really thick, because I had 5 leaf Skyjackers and probably still 1.5" away from tightening it up. I used a dye and rethreaded it down further to make them work.
In any case, both of those studs broke at different times around 5-6 wheeling trips later. No, they didn't break where I added the thread and they were always tight (checked them before every trip), they broke just inside the holes in the D60 housing (what a PITA). I replaced them with grade 8 bolts and have run probably 20 trips with no issues.