The Olfa Ultrasharp Black Heavy-Duty Snap-Off Blades Are Exclusively Designed For Maximum Cutting Performance And Are Ideal For Applications Where Superior Sharpness Is Required.Made From A High-Quality Japanese Grade Carbon Tool Steel, The Olfa Black Blades Are Double-Honed For Extreme Sharpness And Are 25% Sharper Than The Olfa Silver Heavy-Duty Hb Blades. Long Lasting, Durable Snap-Off Blade - A New Sharp Edge With Just A Snap. Blade Container Locks For Safety. Fits Olfa Extra Heavy-Duty Handles. 7 Cutting Edges Per Blade. 20 Blades Per Pack. Good For: Cutting Drywall, Roofing, Leather, Rubber, Etc.