UNEF Thead form

"Limits" makes sense to me.

I certainly don't claim to understand the whole subject either. For instance, the thread tables aren't sufficient to completely specify a good thread. It seems at least one more toleranced dimension is required. I suspect the key is the illustration in my MH that shows the proportions of internal and external thread at maximum material condition, but I've never had a good enough reason to take the time to work through it.

Quite so. That's why I wrote the software, partly to make sure I understood the specification properly, and partly to yield practical machining specs, as opposed to abstract geometry that are all the standards give.