When permanent precision is key, go with a Japanese Pigma Micron ink pen. Their archival quality pigment ink is water-based and quick-drying on porous surfaces. Fade resistant, waterproof, and chemical resistant, the ink does not bleed through most papers and won't smear or feather when dry. The pens come in six point sizes.
005 = 0.20mm line 01 = 0.25mm line 02 = 0.30mm line 03 = 0.35mm line 05 = 0.45mm line 08 = 0.5mm line
Capped barrel measures 5 5/16" long, 3/8" in diameter. Cap has a metal clip. Made in Japan. Not refillable.