I've never found a pen point, even the Extra Fine designations, that would write as fine a line as I see rod inscriptions produced routinely. However, a long time ago I found a way to produce a very fine line inscription. I used a sharp point bodkin (a large, sharp needle should also work) and carefully wrote/dug the script lettering into the surface of the graphite blank, then wiped away the dust. Of course, you have to write slowly and carefully, as there's no erasing mistakes.
Then I smeared gold paint into the lettering, with the little brush in the bottlecap, and immediately swiped away the excess with a rag. The script lines stood out nicely, gold-filled. Then, of course, I covered it with rod finish. It still looks good over twenty years later.