Choose the nib based on the width and inkiness of the line you want, then size up one grade from what you would pick in a Western pen. Sailor cuts its nibs to the Japanese standard, so a Sailor medium lays down a line closer to a fine on a
Lamy or Pelikan. Most Pro Gear Slims here come in extra-fine, fine, medium fine, medium, broad, zoom, and music, while other designs like the Shikiori series pens are sold in medium-fine only. Medium fine is the safe middle: it feels crisp on everyday paper without being scratchy.