On my KitchenAid attachment, that would be setting 6 or 7.
For pasta sheets for lasagna or ravioli, stop at the 2-3 settings from the thinnest setting. On my KitchenAid attachment, that would be setting 6 or 7. I find I don’t use setting 8 because at the point the dough is so thin it’s hard to work with without it tearing.