Mudd Mutt

I put a new pitman arm on my truck and my dad screwed up my steering box putting it back together so I bought a new box from the junkyard and it came with a almost new pitman arm so I just used it and kept the one I bought. That was about a year ago. My dad decided to put the pitman arm on I bought and we couldn't get the old one off. He needed his truck for work so I decided to put it all back together but the pitman arm stud just turned with the nut. I finally got the pitman arm off and put the new one on after breaking my hand doing it and now the stud on the new pitman arm just spins. It's a 91 4x4. Am I doing something wrong or did I buy a bad pitman arm? I bought it new from oriellys a year ago so the receipts long gone for taking it back. It's the stud that goes into the steering shaft.

cleveland63b

the balljoint part that goes into the centerlink spins? or the gearbox?