Cryptic claims a thickness of 2-3 microns for their coatings, but I'm not sure if that's their NiB or not, as they do a lot of other coatings, too. It seems like most NiB coatings are 10-12 microns thick minimum, and go up in the hundreds of microns thick. Between different coating processes and different methods of QC, I wouldn't be surprised if the NiB's too thick, making the bolt fit too tight in the chamber.