These superfine technical illustration pens feature waterproof, archival india ink that will not smear, feather, or bleed on most papers. When used with a light hand, Microns always provide smooth, consistent, and skip-free lines. Perfect for illustration, mix media, journaling, drafting, or accounting. The 3-pen set comes with the following sizes: 01 (.25mm), 03 (.35mm), 05 (.45mm) The 6-pen set comes with the following sizes: 005 (.20mm), 01 (.25mm), 03 (.35mm), 05 (.45mm), 08 (.50mm)