I can't tell you what size they are, but I got a pair some years ago. I have EU size 39 and they fit me perfectly. I'm not sure how much they stretch for people with larger sizes though.
There isn’t any selectable to choose the size of the socks. So It seems that they only have a standard size.
For these kind of questions the best option is to contact the community team because they will give you a precise answer.
Just send an email to email@example.com and they will help you.