Pens don't have that same gritty resistance on paper like a pencil. And although most don't do this, you can buy pencils in varying degrees of "hardness" beyond the #2 you've been using since grade school.
I like F and HB grades, they are soft enough to make a much darker line, but don't smear anywhere near as bad as the B-grades. Another advantage of softer grades like F is that you don't have to press as hard to get a dark line, so they are easier to erase. I did 2 years of drafting in high school and worked as an architectural draftsman in the late 1980s. I have used everything from 9H - very, very hard lead for making fine guidelines, to 6B very soft for messy sketching.
You know, I took a mechanical drawing class and I loved it. Wasn't required for my CS curriculum, but just playing with the tools and making these precise drawings was a joy. They eventually switched that class to AutoCAD only. Pity.
