The Chef's Choice 4643 AngleSelect professional manual sharpener is the ideal solution for both 15 and 20-degree class knives. Using 100 percent diamonds, the hardest natural substance on earth, our patented abrasives sharpen edges faster and easier. This sharpener improves cutting performance by creating 2 distinct facets set at different angles to form a sharp, longer lasting, arch-shaped edge. The first stage sharpens 15 degree straight edge knives, while the second stage sharpens 20 degree straight edge knives. In the final stage, specialized diamond abrasives create a polished finish to both 15 and 20-degree knives. Precision angle control ensures accurate sharpening throughout the entire blade length. This unit is designed to work with both straight-edge and serrated knives.