/r/ wasn't of any assistance; can anyone help me identify this pen?
Post stuff with what they used?
It makes sense to just demonstrate what you made your work with (there's always someone that asks), but personally I think it's better if they do it in a description or something.
It's a technical drawing pen. You refill them yourself and they can do seriously thin lines. I own a Faber Castell tg1-s 0.25mm, a 0.18mm, and used to have a 0.12mm, but that one broke. They are about the sexiest thing in the universe, and if you like to ink shit, get one.