A while ago someone (sorry but I don't know who) posted a layout here that showed how to make a parametrically controlled helix shape. I thought that would be a good basis for making threads so I added some additional components to do this. Here is my first print:

And here is a short video: https://youtu.be/N9wKgQTBH3A

I had to reprint the nut part 4 times to get the proper clearance value for the threads to work smoothly. So I set up a slider to control this. The attached GH file is set for a 6-sided nut and bolt because that is what's standard, but here in the US fire hydrants use 5-sided bolts so normal people can't mess with them.  I think any odd-numbered of sides would produce an interesting and quizzical result.

The thread helix on this part is a 6-fold one; I did that to match the number of sides on the bolt and nut.  But the script allows any number of layers for the helix; more would produce a finer and perhaps more interesting thread.

Since plastic nuts & bolts are not particularly useful I think my next print of this part will be a really big one. Perhaps with contrasting colors for the bolt and the nut.