safety wire. .
There is a pin/dimple in there that keeps the nut on the inner shank.
I think Mike is correct
JoopSJMike said:*after*[/B] the nut is tighten, or is the swiveling action only intended to align things properly before tightening?
If you're talking about a Heim joint ( the pic link doesn't work ) it's witness hole. It's so you can see the threads minimum depth.