The general guidline for threaded fasteners is that they achieve 100% of maximum strength with engagement equal to the diameter. If you look at most commercial nuts, you'll note that their thickness is usually equal to the thread diameter, or close to that, because there's no point to making them thicker.
The reality is that you reach 100% or very close to that before the full engagement. So 4.7mm of true engagement on a 6mm bolt is borderline, but most likely close enough to pass. But there's a catch. The threads on the bolt don't usually go to the end, and odds are there's a chamfer, so while you may think you're engaging 4.7mm, in all likelihood, you're only engaging 3.7mm and that's kind of pushing it.
OTOH- I suspect you may have the nut upside down. Usually Nylok nuts are installed, thread first so the nylon ring ia the last to engage. In your case, it may not engage at all, but better thread engagement is preferable to the nylok feature. If you're concerned about loosening, you can use a nylon paint or even trap a bit of dental floss in the threads to serve as the "nylok".
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