I think my hair is mostly 3a/b. I do have a few tight 3c ringlets but they are a little bit like my white hairs and kind of get lost in the curly jungle. When my hair was short, my curls were tighter and more strongly 3b. The length now pulls the curl out quite a bit so it usually ends up looking like 3a at the ends but merely wavy or even straight toward the scalp.
3a/b, fine, lots of it