The different types of nails files are designed for different uses, so it is important to select the right one. For natural nails, a fine-grit cushion file is gentle yet effective. Basically, the higher the grit number, the smoother the file. Coarse files (80-100 grit) are best for acrylic nail extensions. Medium files (180 grit) are best to shape extensions of medium thickness, like most tips and wraps, and to shape the free edge of toenails. Fine files (240-600 grit) are best for removing small bumps, ridges or discolorations and for shaping the free edge of natural nails. Ultra fine files (600-2400 grit) are used for buffing and shining all types of nails. Files come in a variety of materials including padded cushion files, glass, mylar and ceramic. Avoid metal files as they are harsh and can even split nails.