Nut files: If you want to do serious
guitarbuilding, there's no way around expensive nut files.
These special files, which are available from most suppliers of
instrument-making tools, have teeth on their edges only and produce
accurate, round-bottom nut slots. You don't have to buy all
the different file sizes for making slots of different widths:
wider slots can also be formed by simply rolling a file
side-to-side. The thinnest nut files available are as thin as
sawblades and therefore very fragile. The following four file sizes
would make a good starter set: .016"/ .025"/ .032"/
.042" (0.4 / 0.6 / 0.8 / 1mm). It is also possible to cut out
the slots with a saw first and to continue with a nut file.