Our crowning and dressing files have Diamond Files with specific profiles for the given job. 

The fret crowning files have a concave profile  to achieve the round profile required of the fret

The fret dressing files have a flat profile with all edges ground so the abrasive diamond surface of the file only contacts the fret and nothing else.

These files last for many fretboards: diamond is the hardest substance known and many little diamonds are embedded in a surface plating. As the surface wears new diamonds are exposed. They are equally long lasting on stainless frets and normal nickel silver frets.