I don’t know what it is, but I’ve never gotten on with anything wider than 22mm. If I had to guess, it’s probably because I wear my watch high on the wrist rather than further down the arm. I find that wider straps just are uncomfortable. I purged my collection of anything above 22mm years ago. I suppose I could take the bracelet off of my GMT and try some of my existing NATOs on it to see if 22mm NATOs are an issue. Generally, I like to have as much taper as possible on a bracelet or strap because I find it much more comfortable than having a thick, wide strap on my wrist. I have lovely, sweet dreams about bracelets that taper from 20mm to 16mm.