Better than the usual:
Sapphire files from Pfeilring.

The Pfeilring factory in Solingen has made a name for itself worldwide with the production of manicure tools - the good reputation of its sapphire nail files is still unchallenged. Two-thirds of the sapphire stones are embedded in the galvanised steel blanks, so they cannot break out even after long use; the file surface is sealed with chromium plating (hence the blue glow) - nail calluses do not stick and they are easy to remove. The corners are smoothed to achieve a continuous surface. Pfeilring manufactures its nail files with black galalith handles exclusively for us.