When To Use Each Grit?
Nail files are graded according to the grit per square inch. For instance, 80 grit will have 80 pieces of sand in a square inch. A wrong choice of grit could damage your clients nails. Using the correct grit for every situation is crucial for your nail protection.

80 grit: Extra Coarse-This grit level is helpful for removing gel overlays or for shortening artificial nails. It is not recommended to use it for natural nails.
100 grit: A bit coarse but still can be used for shaping the sidewall of artificial nails or for shaping hard toenails.
150 grit: If you want to blend your nail tips, then 150 grit is a great option. You can use it for over-the-top filling.
180 grit: This one is the medium file, and its used in the nail plate preparation. You can use it to give a beautiful shape and nice, smooth finishing to artificial nails. However, if your nails are hard, then dont use it for natural nails.
240 grit: It is the softest and finer grit. You can use it to shape your hard natural nails. You can use it in the nail plate presentation before the enhancement product.
4000 grit: This grit is the smoothest one and is used to remove ridges and make the nail surface smooth. These are the finest files and consider as finishing files.

*Keep out of reach of children