The Olfa UltraSharp black heavy-duty snap off blades are exclusively designed for maximum cutting performance and are ideal for applications where excellent sharpness is required. Made from a high-quality carbon tool steel, the Olfa black blades are double honed for extreme sharpness and are 25% sharper than the Olfa silver extra 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.