Keeps jointer knives and planer sharp without removing them from the machine. You can quickly and easily restore jointer knives to crisp, sharp edges with Diamond HONE:MATE. Diamond HONE:MATE has two different grits which do a finer job of sharpening (180 & 400 grit) Positive index system keeps sharpening angle accurate and does not bind knife in the stone. Use oil for cooling and lubrication. THE COMPETITION:Both stones are the same grit. Single grit stones do not provide same sharpness as two-stone systems. Indexing system is not as accurate or positive and knife binds in the stone. USA.