The ball joints have 1/2" (13mm) threaded rods (male) and the shaft is threaded 7/16" (11mm) to receive them (female). Alt 1.

Measurements:

The shaft is 20mm in the middle.
The shaft is 18mm at the ends, from the end to 60mm toward the middle from each side.

I list them this way because the ball joints seemed closer to imperial dimensions and the shaft seemed closer to metric but I am not a machinist and I couldn't say. I measured them with a digital caliper so I did notice that about them though, although they were not far off from either unit system i guess with tolerances.

Also, there are approximately 10 threads every 12mm so maybe it is metric?

Finally, while measuring I saw a stamp in the shaft W740. Is this a 740 center link? If so I am in the wrong forum. ;)

Thanks!