I wanted to buy a good quality set of Luthier's nut files to very slightly deepen the string slots in the white composition nut on my Fender American Standard Precision Bass.
When holding the string down at the 3rd fret, clearance between the bottom of the string and the top of the 1st fret, should be the thickness of a thin piece of paper. (.006" or 0.15 mm)
These files are double edged.045" / .085" - .065" / .105" - and .075" / .130" perfect for the string sizes on the majority of 4 and 5 string basses.
I sorted out my P bass in less than 5 minutes. Excellent.