In addition, if the width is less than 2, the effect of writing Gothic is not obvious. 2.4-3.8 is recommended unless there is special need.
To sum up, if you usually use normal capitalization, use about 2.4, if you use millet, use about 1.5, if you use oversize, use about 3.8, and if you have special purposes, you can choose a bigger one.
Ps: I haven't used speedball. I went to see it yesterday. I recommend C2+C3. If you need to choose one, it depends on whether you are used to writing in big letters or small letters. C3 is 2mm smaller and C2 is 3mm wider.