Ian, I need to check that measurement, I said I "think" that it was 7.17. 9:45 pm here, I'll check it tomorrow. One thing certain, that is a strong thread. In any case that is .17 of a mm, it works good.
Digital caliper, not the most expensive in the world, but the drill size is definitely 19/64. Only 1/64 less than the "correct" size.
Anyhow, it works fine and I am more than happy with the bolts/nuts.