I want to verify that the rear brake line flare nut on the 89-91 hatchback is a 10mm?

Everyone I know personally has said it is, but mine seems to have enough play when I put a 10mm flare on it that I’m causing some rounding. It almost seems like it should be a 9mm, which seems extremely odd to me. I had to hunt for a long time just to find somewhere that had a 10mm flare wrench for me to use. If it’s actually something smaller Id like to return it and go hunting for the right size. If it is supposed to be a 10mm, then it may be time for another plan..

I think I’m going to have to use vice grips to remove it, unless anyone has any little tricks for it they want to share?