Rep Power: 0

I changed one of my front axles today. It went fine, until I went to put the castle nut back on the lower ball joint. The problem is that the bolt turns, when I'm trying to tighten the nut, and there's no head on the top of the bolt to hold it. How is that bolt supposed to be held and not turn? Do I have to replace the lower ball joint to get a new bolt? I don't otherwise need a new lower ball joint.

Does anyone have any other ideas? It's a 93 Civic DX.

thanks for any help you can give,
Bill