Tie Rod won't torque?

[swissarmychainsaw]

I am replacing all the tie rods, idler arm, pitman arm on my 1975 GMC c15 Rwd 350/350.

I got everything back together, all aligned (shade tree version), and the last
tie rod (outer, passenger side) when I go to torque it down, the stud turns!

I can see the cotter pin hole moving around with the castle nut.

Does this mean I have a bad tie rod, or a bad Steering Knuckle?

I'm thinking that the two mating surfaces of the Tapered stud (tie rod) and the Knuckle are what keep it from turning? So am I not getting enough contact, or is it just a bad tie rod?

Thanks!
Nick