This nail file will use when trimed your nail's shape or made a even nail's surface. Because of named grit with a thickness of particle, so the low-number's side uneven , the high-number's side more even. you should be use even side when trimed your real nail's shape, and you should be use uneven side(100 grit) when take off residual artificial nails or you want make a even nail's surface. should be use 180 grit file when you want make even the whole of artificial nail's surface. It was most comfortable way that take one side with a thumb and then take the other side with the rest of the finger.