I specifically mentioned “Mexico” because the Nicholson files that were made in Mexico were completely unusable ****.
The steel used for the Mexican made files seemed yo have had the surface decarburized, preventing the steel from being hardened.
I don’t know whether the grinding/sanding step used after forging was skipped, (this removes the outer decarburized layer of steel), or whether the files were simply heated wrong at some point during manufacture, but it was possible to shave steel off the surface of the Mexican Nicholson files using a Swiss Army knife, which normally should be softer than the file teeth.
I believe Apex/Nicholson realized the issue, and shifted production, or maybe fixed the process somewhat, but the Mexican made files were basically unfit for use on metal.