KUM Artists Sharpeners are without peer with regard to materials and manufacture. KUM sharpeners are equipped with blades manufactured with ultra-hard (65 hrc) and razor-sharp high carbon steel. The blades on a KUM sharpener are harder than ball bearings or any high-quality knife, providing you with the ideal instrument to sharpen the hard, quality graphite found in Artists pencils. KUM blades are slightly curved rather than dead straight. The curved blade means the edges are under constant tension and not lifted by pressure during sharpening. This provides a consistent sharpen to the pencil and prevents the pencil tip from springing out or tearing. Additionally, the pressure against the screws prevent them from loosening.