Black ballpoint has a medium 1.0 mm tip
Blue ballpoint has a fine 0.5 mm tip
Smooth ballpoint ink refills are for all Moleskine ballpens, roller and click roller pens.
As an international size, it also fits other pens like Parker ballpen.
Clean, bright, developed specifically for the paper used in Moleskine notebooks.
Roller gels are larger "Plus" size and have a medium 0.7 mm tip