There are two sets of nomenclature for describing a file’s “grit”
For American pattern files, there are three classes, Bastard,
Second, and Smooth cuts. These are listed from course to fine.
Gorbet, or Swiss Pattern Files use a numbering system which is
00 14 teeth per inch
0 51 teeth per inch
2 79 teeth per inch
4 117 teeth per inch
While I don’t have an exact conversion from one type to the other,
it would be safe to equate a Bastard to a 00, a Second to a 0, and a
Smooth to a 2. In my years as a machinist and machine repair, I
never saw a 4 grit file until I got into jewelry.