FILE UNDER “WHAT’S GOOD” Not all emery boards are created equal.

RULE OF THUMB The higher the grit number the finer the file. Natural nails require a finer grit (about 180 or 240; anything lower could cause breakage). If you have gels, opt for a medium grit (100), and if you’re trying to shorten your Kylie Jenner-inspired acrylics, use a coarser file (80 to 100). THE BIGGER THE BETTER Smaller files require a steadier hand, so if you’re an armchair manicurist, stick with the full-size version. ALWAYS SWIPE RIGHT Filing nails in one direction will avoid tearing and breaking them, says Rorong. CONSIDER

GLASS Glass or crystal files prevent splitting by sealing the keratin at the tip of the nails. From top: Sephora Collection Crystal Nail File ($12.50); Tweezerman Neon Hot Nail File ($6.49); Dimancel Flexible Diamond Nail File #2 Medium ($28); H&M Straight Nail File ($4 for five); Quo Nail File ($15; part of a manicure kit)