A straight hand file in 100/180 grit, slim profile. The straight profile is the one for squaring off and for filing along the sidewalls where a curved file rocks.
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.
