Twist mechanism missing something? Ballpoint.

[Liuna]

Greetings. I've acquired 3 nice Cross Classic Centuries. The matte black ones are alright, have very little scratches, they work fine.

There is a sterling silver one which I can't screw together, as if its twist mechanism was too long into it. Maybe it's not its own twist mechanism? I've also noticed there was some threading within the black one's mechanism, the sterling's doesn't.

What could be done to repair it? These 3 are my first Cross pens. 

 

I attach some photos. Thank you in advance.

[Liuna]

It turned out it was missing this part of the mechanism (the pen on the photo is a different one, not the sterling). The copper part.