Nut is better than loctite, as the latter will make future adjustments difficult, you'd need to heat with soldering iron each time. I can't recall size of nut, but if I had to take a wild-@ss guess, it would be same as rack braze-on threads, so 5mm dia x 0.8mm pitch? Don't disassemble the latch on carpeting, as I recall there is a tiny circlip holding the pivot pin, don't lose that. While you're at your local bolt and nut monger, good idea to pick up a couple spare circlips for there and other hinges.

It's amazing how a few tiny improvements make a big difference on these folders.