I've done ball joints before, know how to do it. But just picked up one of them for my jeep and it looks a little odd to me. The treads below the castle nut slide off as well. What are they, what is their purpose?

 

Had the same experience. Bought mine from Autowrong and went back as I figured the counter jockey pooched it. The explanation I got was that the ball joint has other applications where that threaded sleeve is used but you just toss it for a Cherokee which I did. The joints worked fine but top joints aren't easy to getting going in straight. Chamfer the leading edge with a file to help.

 

Yes, you toss that part. The XJ doesn't use it. A Dana 44 uses that style insert.

 

Ok thanks guys. I'm just doing lowers. Uppers are fairly new