FriXion Synergy Knock is equipped with a proprietary "Synergy Tip" that has a smooth writing, good writing and a strong nib. The "Synergy Tip" combines the best of pipe tip and cone tips, and has a high quality nib with "smoothness" while fine writing. The ink color is represented in the grip and the body is unified with a smooth matte gray feel. Universal design for long lasting use. The color of the eraser rubber on the back varies by diameter of the ball so you can easily distinguish the pen with multiple ball diameters. 0.01 inch (0.3 mm) type with the finest friction history.