Hosco Japan Nut File 024″

A high quality nut file. A string seated in a properly filed nut will have the correct height and will also prevent extraneous string noise from the nut.

0.024″ / 0,61 mm width.

A typical set for classical guitar would contain the following files:

0.028″, 0.032″, 0.036″, 0.042″

A typical set for electric and acoustic guitars will depend on the string gauges. Always check the package for the string gauges and use the same file gauge accordingly.
A great aid in filing nuts is the H-GB4 Hosco GrooBar. This will prevent you from filing the string slot too deep.