The sky sharpening paper used Sumitomo 3M's Tri-Ait, but we changed it. Abrasive grains are firmly peeled off so it will cut long. 3M has poor possession. However, because the abrasive material is different, I think it is coarser than the display granularity. Specifically, the motor sign # 240 is 3 M's # 120, the motor's # 320 is 3 M's # 240 feeling. If you care about choosing the number, it will expire long and it is cheap, so I will do the next one.