With a few simple hand tools and a lot of patience, you can adjust a banjo nut. Take precise measurements of the fret height on your banjo neck to begin. After you’ve measured the height, stack a set of feeler gauges to that height, then add another very thin feeler gauge on top of that. The string grooves in the banjo nut can be deepened with a small file to allow the strings to ride closer to the banjo neck. You must decide how close your strings should be to the nut in relation to the frets in order to avoid buzzing.
Because the instrument is shipped this way from the factory, the typical adjustment of a banjo nut is high off the frets. This makes the instrument difficult to play and can cause finger soreness after just a few minutes. The high adjustment is commonly used to eliminate fret buzz caused a nut that is too close to the height of the fret. Many music stores offer professional setup on new purchases; however, with a little effort and patience, you can do it yourself. Working slowly and taking frequent measurements and trial tunings for each string position to be worked on is the key.
The key is to take precise fret height measurements, which is the distance between the fingerboard and the top of the wire frets. After being measured, a set of feeler gauges stacked to the proper height is placed directly behind the nut on the fingerboard of the banjo neck. You’ll need to decide how much extra height you want your strings to have above the frets, and then place that size feeler gauge on top of the stacked feeler gauges.
Start removing one string from the banjo nut’s groove and running a small file through it at a right angle to the banjo’s tilted head stock. Stop filing when the file reaches the feeler gauges, and replace the string in the groove. Tighten the string and tune it while keeping an eye out for any signs of fret buzz. Continue filing the remaining grooves in your banjo nut to the same depth if you’re happy with the new action of your banjo strings. It’s also important to remember to do the same thing with the fifth string banjo nut.