On the zBar of a b body there is a steel clip that attaches to the bar itself out near the frame side of the zbar. When you insert the mounting ball and the plastic bushings that go into the Zbar, Is the groove in the plastic bushings supposed to be held into place by the two metal tabs that protude into the inside of the Z bar from the clip, or are they just there to act as a stop so the bushings don`t go in too far??

I'm wondering the exact same thing.

The ends of the clip should engage the groove in the plastic bushing, locking it in place.

Great, thank you for your help. Makes sense now.