A few Victorinox Swiss Army knife models include a special version
of the hook which has a rough spot
on one side, designed to be used as a nail file.
This tool was introduced in the mid-1990's.
Uses: The file surface is not quite as big as the regular nail file found on many of the smaller Victorinox knives, but its position on the back of the narrow hook often makes it more convenient to use than a flat file.