High-grade pens are interchangeable, and all kinds of pens are different in thickness. Generally, EF is suitable for fine print, and f is suitable for daily writing (not suitable for students, because the space given by that exercise book is really. . . ), m is suitable for signature. The rubber stick pen holder is made of rubber and the steel stick is made of stainless steel, so the rubber stick is soft to hold and the steel stick is heavy.