With the introduction of high-carbon stainless steels, comes the need for a more aggressive sharpening surface than a conventional whetstone can provide. The DMT line of sharpeners incorporates a monocrystalline diamond face embedded in a nickel base for a lifetime of durable, dependable service. The blue DMT sharpeners are rated at 325 mesh, while the red is rated at 600 mesh. These diamond sharpeners are a must for anyone who wishes to sharpen a steel in the 60+ Rockwell hardness range.