Koh-I-Noor Hardtmuth Graphite Leads are made of the highest quality graphite; Lead Diameter - 3.2 MM ; Grade - 6B is suitable for use with mechanical clutch pencils. Ideal for use on newsprint, Bristol, colored paper or heavily textured surfaces. 8B-3B are for Graphic and artistic purpose, 2B-F are for Office & School Supply, H-10H are for Technical Drawing and Lithographic purposes.