This is totally fine for use on natural nails. Emery is a very hard rock that is ground into an abrasive powder which is used to make the boards. The grit is usually 150 - 180, but they vary.
Accordingly, what is a 240 grit file used for?
240 grit: This is a softer grit file and is frequently used to obtain a smooth finish or buffing artificial nails. 500 grit: A file with this grit is extremely soft and usually only used to polish the surface of acrylic or gel nails.
Are metal nail files bad for your nails?
Because this is one of the most abrasive nail tools, using it on natural nails is not recommended. The coarse grit used in metal files tends to cause nail damage. So, if you're using this type of nail file on your natural nail, we beg you to stop.
Is there a difference between an emery board and a nail file?
A nail file is a tool used to gently grind down and shape the edges of nails. They are often used in manicures and pedicures after the nail has been trimmed using appropriate nail clippers. Nail files may either be emery boards, ceramic, glass, crystal, plain metal files or metal files coated with corundum.