Nail files carry a number that most people ignore. It describes something specific, and matching it to the task prevents most of the damage attributed to filing.
What the number counts
Grit refers to how many abrasive particles occupy a given area of the file surface. A higher number means more particles, each of them smaller.
More, smaller particles remove material more slowly and leave a finer finish. Fewer, larger particles cut faster and leave deeper scratches behind.
The scale is therefore inverse to what people often assume: a low number is aggressive and a high number is gentle.
Why natural nails need high grit
The natural nail plate is built from thin layers of keratin bonded together, and it is far softer than any artificial enhancement.
A coarse file tears through several of those layers at once rather than cutting cleanly, which separates them at the free edge.
That separation is what appears later as peeling and splitting, and it is usually blamed on diet or products rather than on the tool.
Enhancements need lower grit
Acrylic and hard gel are considerably denser than natural keratin, and a fine file barely marks them however long it is used.
Shaping those materials requires a coarser file, and technicians move through progressively finer grades to remove the scratches left by the previous one.
Using an enhancement-grade file on a natural nail is the single most common misuse, because the two look almost identical in a drawer.
Direction matters as much as grade
Sawing back and forth pushes the layered edge in alternating directions, working them apart even when the grit is appropriate.
Filing in one direction from the side towards the centre keeps the layers pressed together and produces a cleaner edge.
The difference is most obvious on nails that are already thin or that have been through repeated enhancement cycles.
Buffers are a separate category
Buffing blocks operate at very high grit numbers, and their purpose is smoothing and shining rather than removing length or shape.
Even at that fineness they remove surface material, so repeated buffing thins the plate over time and makes it more flexible and prone to bending.
Files also wear out. Particles dull and detach with use, so an old file cuts unevenly and requires more pressure, which reintroduces the damage the correct grade was meant to avoid.
Glass and crystal files sit outside the grit scale entirely, since their abrasive surface is etched rather than particle-coated and does not shed material as it is used.