Quick read: A nut slot should be slightly wider than the string — about 0.002 to 0.004 inch over the gauge for plain strings, and enough to clear the winding for wound strings. Wide enough that the string drops to the bottom and glides on a bend; narrow enough that it can't shift side to side. Too narrow binds and pings; too wide buzzes and slops, and it's the usual cause of an open-string buzz that vanishes the instant you fret. Match the file to the string, cut undersize, and open the slot in small passes — you can't un-file it.
Most nut advice starts with lubricant. That's backwards. A slot cut to the right width and shape barely needs lube, and no amount of graphite fixes a slot that's the wrong size. Width is the first decision, and it's the one most people get wrong in the same direction — they open the slot too far, chasing a binding feel, and trade a tuning problem for a buzz.
So before the file touches anything: how wide should the slot actually be?
The Clearance Rule
A nut slot is a guide, not a clamp. Its only job is to set the string's height and side-to-side position at the open end of the scale, then get out of the way so the string can move freely when you bend, tune, or use a trem. That means the slot has to be wider than the string — but only just.
The rule is: slot width equals string gauge plus a hair. For a plain string, that hair is about 0.002 to 0.004 inch — most luthiers cut with a file three to four thousandths over the string and call it right. For a wound string, the slot has to clear the outer winding, not the core, and a touch more — the winding has to slide without the slot pinching the wraps.
The feel test is more reliable than any number. Seat the string and check two things:
- It drops to the bottom of the slot and stays there. It doesn't perch on the slot walls.
- It glides. Push the string toward the fretboard at the nut, or bend at the third fret — the string should move through the slot without a tick or a ping, and return on its own.
- It doesn't rock. Wiggle the string sideways at the nut. If it visibly shifts in the slot, the slot is too wide.
Glide without slop. That's the whole target.
Width by String Gauge
This chart covers the two most common electric sets and the file size that lands the clearance rule without overthinking it. The file numbers assume gauged nut files, which cut a slot a few thousandths wider than their stated size — that built-in over-cut is your clearance, which is why the recommended file often matches the string number rather than exceeding it.
| String | Gauge (in) | Slot width target (in) | Suggested file (in) |
|---|---|---|---|
| High E (10–46 set) | 0.010 | 0.012–0.013 | 0.012 |
| B | 0.013 | 0.015–0.016 | 0.016 |
| G (plain) | 0.017 | 0.019–0.020 | 0.020 |
| D (wound) | 0.026 | 0.028–0.030 | 0.028 |
| A (wound) | 0.036 | 0.038–0.040 | 0.036 |
| Low E (wound) | 0.046 | 0.048–0.052 | 0.050 |
| High E (9–42 set) | 0.009 | 0.011–0.012 | 0.012 |
| B | 0.011 | 0.013–0.014 | 0.013 |
| G (plain) | 0.016 | 0.018–0.019 | 0.018 |
| D (wound) | 0.024 | 0.026–0.028 | 0.026 |
| A (wound) | 0.032 | 0.034–0.036 | 0.036 |
| Low E (wound) | 0.042 | 0.044–0.048 | 0.046 |
Two notes on reading it. First, the wound-string slots run a little more generous because a winding needs more room to slide than a smooth core of the same diameter. Second, if you fall between file sizes, round down. An undersize file plus a couple of extra passes always beats an oversize file and a slot you can't take back.
Too Wide: The Four Failure Modes
A slot that's too narrow announces itself — it pings, it binds, the string goes sharp when you tune up and won't come back down. That's covered in the string-pinging diagnostic. A too-wide slot is sneakier, and it shows up in four ways.
1. Open-string buzz that disappears when you fret. This is the signature. The string rattles against the walls or front edge of an oversize slot when it's ringing open. Fret the first fret and the nut is out of the circuit, so the buzz is gone. If a buzz follows that pattern, stop checking the truss rod and frets and look at the nut.
2. Sitar rattle. A slot that's both too wide and too flat (or back-sloped) lets the string contact the front edge of the nut as it vibrates, producing a buzzy, metallic, sitar-like overtone on the open string. Width makes it possible; the wrong floor shape triggers it.
3. Side-to-side slop. If the string can shift in the slot, its position over the neck isn't fixed. That moves the speaking length a hair, which nudges open-string intonation, and it changes the string spacing feel under your fretting hand at the first few frets. On a guitar with a trem, the string can settle in a slightly different spot after every dive.
4. Strings that pop out on bends. This one mostly bites the plain G and B. Bend hard at the nut end of the neck and an oversize slot can let the string climb the wall and jump out entirely. It feels like a hardware failure. It's a slot that's too wide to hold the string where it belongs.
Here's the part that surprises people who assume "more clearance is safer": going too wide doesn't just fail to help tuning stability — it can make it worse. A loose string seats in a slightly different position each time it returns from a bend, so the open note doesn't land in exactly the same place twice. The slop that was supposed to cure binding becomes its own tuning problem.
Width First, Then Shape
Getting the width right is necessary, not sufficient. A perfectly sized slot still buzzes if the bottom is flat instead of gently radiused, or if the high point of the slot (the witness point) is at the back instead of the front edge. The string has to break cleanly over the front edge of the nut — the side facing the fretboard — and ramp down toward the headstock behind it. Width sets whether the string fits; the floor geometry sets whether it rings cleanly. The slot geometry guide covers the back angle, bottom radius, and witness point once the width is dialed.
And once the slot is the right width and shape, the lube question gets small. A slot that holds the string snugly and lets it glide doesn't grab in the first place — so the choice between graphite, nut sauce, and the rest, covered here, is a refinement, not a rescue.
If It's Already Too Wide
You can't file a slot narrower, so a too-wide slot means adding material back. The standard shop fix is a paste of thin cyanoacrylate glue and bone dust (baking soda works as a filler too, and accelerates the cure), packed into the slot, leveled, and left to harden. Then you recut the slot to width with the correct gauged file. It's a clean repair for one or two stray slots.
If three or more slots are oversize — common on a factory nut that was cut for a heavier set than you run, or cut carelessly — filling each one is fiddly and the result is a patchwork. Replacing the nut and cutting all six slots fresh to the chart above is faster and more consistent. Either way, the target doesn't change: slightly wider than the string, never loose.
