These are steel triangles blanketed in a bonding agent then covered in diamond particles. Diamond hard abrasives are recommended when you wish to remove stock, for restoration purposes and to aggressively re-shape, re-bevel and re-profile a cutting edge. Sold in a pair, 204D triangles fit into the 204 Sharpmaker sharpening system. To Clean: rinse in fresh water. By Spyderco.