Confusion about crochet hook size

I bought a new Crystallite crochet hook in a size N. I got it home and the package said it was a 10 mm. However, my aluminum Boye hook is also an N but it’s a 9 mm. My Boye is an old hook. What’s going on here? Did the mm sizes change for this size over the years?

The sizes may change depending on the brand. I know some of my older boye needles are larger than the newer ones in the same size too.

This is probably why they’re giving me a mm size rather than a letter size on Youtube tutorials.

Yeah, it’s better to go by mm because not all needle sizes are the same mm. In needles, there’s not always the same size in the smaller ones (US sizes 1, 1.5, 2) there’s some mms in between, and Clover’s US 6 is 4.25mm while everyone else’s is 4mm. I imagine the hooks are like that too.

Someone else told me that N hooks are popular. Probably because they make quick blankets. They said that there’s a difference in mm between the two companies, Boye and Bates. My Crystallites are from Bates/Coats and Clark/Red Heart. Then they have the L and M sizes in between that I had never heard of before. It’s been a few years since I picked up a hook. I feel like Rip Van Winkle, asleep for 20 years.