Every PDF I have just skips by that information.
I'm going to undertake a proper Internet search on this one. Prepare to scream ... all articles that I could find, including the vfaq.com references in the turbo section, show everything but that spec. Very frustrating I know, but wouldn't it be best to tighten the nut to the spec that such a nut and material are designed for? I've gotten away from those specs but most repair manuals, like the infamous Haynes ones, show this type of info in the first 20 pages or so. It, then nut, looked like a locking type of sorts when I last saw my setup. Sorry I couldn't be of more help on that one.