A half-moon hand file in 100/180 grit. The half-moon shape follows the curve of the free edge, so you shape in one pass instead of correcting a flat file into a curve.
Reading the grit numbers
Two numbers means two sides. The lower number is the coarser face, for shaping and taking length down; the higher one refines the edge afterwards. 100/180 is the working pair for shaping natural nails and gel; 180/240 is finishing only, too fine to remove much length.
