A weird thing happened to my Sheaffer Prelude

[akapulko2020]

Its a lovely pen I have received as parting gift from co-workers some good 10 years before coming back to my fountain pen hobby. It writes lovely, or at least,used to..
I recall cleaning it and not putting it back together some time ago, but now it seems I *can't* put it back together as it looks like the black part has become too wide (??) to enter the nickel colored part properly ( I'm not entirely sure of the proper terms for them in English)
See pictures.

Any ideas what could have happened and how do I fix it?

Thanks in advance

Pens. And Notebooks

[Jon Szanto]

What you are saying is that you can no longer thread the section (black part) into the barrel (silver/nickel) of the pen? It should simply 'screw' into place with a clockwise motion. I would look straight into the empty barrel and make certain that the opening hasn't gotten compressed any, so that it became out-of-round (or oval). It would need to be round for the section to fit in. If that is the case, gently flatten it in the opposite direction to try to put the opening back into round shape. You should then insert the section and screw it back in. Sometimes it helps to rotate counter-clockwise until you feel a little 'click', which means the threads have caught, and then screw it in clockwise.

If it really can't fit inside the barrel, I'm not sure what to say. Plastic usually shrinks, and doesn't expand, so I'm a bit at a loss if that is what has occurred.

[akapulko2020]

Yes, that's exactly it. The section actually only can get right before the threading starts on the barrel. :/

Pens. And Notebooks

[akapulko2020]

Yessss. Tried to flatten it this and that way and no idea whether that was the problem or there was something small and clear stuck on the threads but I can screw it on now. Thanks a bunch @Jon!!

Pens. And Notebooks