PIC are interesting stands. All of them I encounter were very skinny and very portable. Old school, but totally usable today. Still have 4 or 5 of them. Very easy to maintain and fix. If you can't fix it, just buy another for $5 and keep dysfunctional one as donor for parts.
The problem I seem to keep encountering is the proper screw. I've tried various thumb screws but non are doing the trick. But, the thought of a machinist might be fruitful. I'm going to give that a try - someone who knows what other parts might work.
Working on screw should not be a problem. If a proper one is not at hand, any mechanic should be able to shorten one, cut a new thread, weld another head on etc. up to machining a complete new one.
You might show us a photo of your problem.
Fwiw, I'd just wander over to the hardware & try some regular screws It was US made & won't be metric.
That'll give you the proper size.
Now ya gotta find the file of specialty screws, knurled, thumb & wing. The key there is to just ask someone
where they keep 'em. Some might come from from an auto parts store.
Going back to the first sentence, once you know the size you can probably order it from Grainger.
Filmtools sells t-handles (the sort of knobs that are on pro light stands) in a couple sizes - the 1/4-20 ones are fairly small, and it's a common hardware and tap size. Most big hardware stores have smaller threaded screws with plastic handles, too, usually in parts drawers… handy for fixing stands or making oddball camera rigs.