This is the height the strings are set above the fretboard. This is why we straightened the neck first. Measure the height of the strings at the 12th fret on the fretboard. The strings should be above the fret about 1/4 of an inch. A low string action is about 5/32 of an inch and the high string action is about 5/16 of an inch at the 12th fret. The string action must be in this range or you get string buzzes with too low an action, or the notes will be stretched out of tune when fretted from too high an string action. Too high a string action may cause finger tip damage (blisters), and it reduces the speed at which you can play easily. If the string action is too low or too high, it must be adjusted to make the strings more playable. Last, the string action height at the top nut. This height can be measured with feeler gauges or the skinniest guitar pick. This string height above the fret is the most critical for easy playing.
The strings must be above the first fret by at least twenty-thousands (.020) of an inch or the strings will buzz. If the strings are higher, then the strings are much harder to push down than necessary. Lowering the string height on the top nut is best done by an experienced person. This is where the string grooves in the nut are cut with a small saw blade that is the thickness of the string. The string angle in the nut is critical to provide accurate noting and prevent buzzing.
In the next article, I will discuss adjusting the string action height using the coordinator rods in the back of the banjo, and correct placement of the bridge.