Do you know what a mandolin nut is? No, it’s not a musician who absolutely loves mandolins to the exclusion of everything else. It’s actually a part of the mandolin.
A nut is the piece at the end of the fingerboard that keeps the strings properly spaced apart (and at the right height). Most stringed instruments have a nut.
Purpose of the nut on a stringed instrument
The most obvious reason that an f-style mandolin (or other stringed instrument) has a nut at the end of the fingerboard is to keep the strings spaced apart at proper intervals. Without it, the strings would wander around, rolling out of the way every time you tried to fret a note.
But there is more to it than just keeping the strings where they belong.
It is also a crucial part of the instrument in the context of keeping the instrument in tune. The strings ride in grooves that are sawn into the nut. If these grooves are too deep, the strings will be too close to the frets and they will buzz and rattle when plucked. But if they ride too high, there will be too much of an intonation change when a string is fretted. In fact, each string — or set of strings — requires a groove of a different depth to ensure proper intonation.
Why do some mandolins have a zero fret?Because of the difficulty in cutting the grooves of a nut just right, some luthiers use a zero fret. This is a fret that’s located adjacent to the nut; it holds the strings at just the right height and does away with the need to precisely set the depth of the nut grooves.
When an instrument has a zero fret, it the nut serves simply to space the strings, nothing else.
Generally, the presence of a zero fret on a fretted instrument like a mandolin or guitar indicates that the luthier is saving himself some time and effort. It’s probably unfair to say that it’s the mark of a craftsman who lacks skill, but this isn’t something you will find on high-end instruments.
Mandolin nuts can be replaced
Nuts are replaceable. A luthier can easily remove a worn or damaged nut and slide in a new one. He may need to make it himself, but this isn’t particularly difficult.
Odds are, you’ll never need to replace your mandolin’s nut, so you can sleep well at night!