An issue that gave me some problems early on with these kits was that the plastic threaded insert was not well fastened to the metal hardware.
If the nib end was pushed while threading it, the plastic would slip up into the cap end. It seemed like the threads stripped but it was just that the threads were now too far from the end to engage. My solution was to CA glue the plastic insert to the center band metal part, before any assembly.
The newer Artisan kits seem to have the plastic firmly pressed into the metal but I always check anyway.
Another solution is to use a small dab of epoxy around the outside of the plastic section before assembly. I've seen this on some directions.
As I recall, and don't quote me on this, but this is different than the very early ones that were the less expensive apprentice variety that had painted metal threads, which was a bad idea.