Since I retired I am back into my lifelong passion for working on my vehicles, I'm up to 5 now. I've been buying automotive primary wire at the parts store but we all know how expensive that is, and the rolls are small. So I have a lot of stranded THWN left over that I'll probably never use, today I used some of my #10 THWN for a fan circuit on the RV. Not much difference that I can see, the strand count looks a bit less on the THWN but the insulation feels tougher. They both seem to have about the same flexibility and unruliness wink I sleeve it all in corrugated split loom anyway.
Anyone else do this or see a problem?