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Luthier Tools - Guitar Nut Filing System


GMC Luthier Tools Guitar Nut & Saddle Tools includes a unique system for shaping a new nut, marking out the precise string spacing and filing the nut action.


Most guitars are supplied with uniform string spacing. With uniform string spacing, the space in between the strings decreases as the strings get thicker towards the bass. This can be quite significant for adjacent roundwound and heavy gauge strings.


The system uses compensated string spacing. With compensated spacing, the string spacing is incrementally increased so that the space in-between adjacent strings is similar across the fretboard. This allows a little more room for easier playing on the heavier gauges and in many cases, it is also possible to increase the overall 'E' to 'E' for even greater comfort.

To get the best spacing for your guitar, we recommend setting the overall string spacing to the maximum that the guitar will allow. A small increase without encroaching on the fret chamfers is often achievable.

This system is accurate and repeatable. A specially made string position marker and guiding template ensure the strings are precisely positioned along the nut. This avoids any discrepancies with individual hand marking out of each slot as all of the slots are cut in the same setting.

The most unique feature of this tool is its comparison of the instrument. The jig is set up directly from the guitar. Different string spacings can be easily experimented with and fretboard offcuts make ideal test pieces for practice nuts.

Should you need to do so, a precise re-make/copy of the nut is simple & quick with the jig already setup for the guitar.

Please see the Workshop Guitar Repair Blog for short videos of the tools application.


The central component of the jig is the Guitar Nut & Saddle Vice.


The vice makes a comparison of the instrument by gauging the bottom of the nut slot using a sliding plate arrangement (similar to using a vernier depth gauge).


After making the comparison, the jig plates are locked together. This creates a datum reference on the jig identical to the guitars nut slot depth.

Gauging the Guitar Nut Slot Depth
Jig For Setting Correct Guitar Nut Height


The nut is placed in the jig and locates on the vice datum. The nut is clamped using the top profile template. The choice of template will  depend on the radius of the fretboard.

The purpose of the template is to provide an accurate reference for the top profile of the nut and leave a minimal amount of material for nut filing.

The nut top profile template is designed with an increase in height from treble to bass. This will leave approx 0.5mm (0.020”) stock material for nut filing at the treble side, and 1.0mm (0.040”) at the bass side. (See photo below - String Action Template).

The jig backplate is lower than the height of the template and will allow the top of the nut to be angled/shaped for relief as shown in the photo.


After shaping the nut, it should be removed from the jig and the overall string spacing marked on the top with reference to the instrument.

Setting the overall string spacing
Guitar nut top profile


The nut is re-fitted to the vice and the the String Action Template fitted.

Note - as the string action templates are smaller than the top profile templates, the top face of the nut profile can be seen with an increase in height from 0.5mm at the treble to 1.0mm at the bass.


The spacing guide is supplied with a string position marking saw. Charts are provided for easy reference to the spacings obtainable.

The system ensures precise positioning and avoids discrepancies with individual hand marking out of each slot.

Guitar string spacing template
Guitar nut string spacing sizes

The guide is adjusted left or right until the required string spacing is found (2-slots on the spacing guide line up with previously marked overall positions on the nut - see photo below left). The charts can be used for reference to confirm the overall string spacing selected. Moving the string spacing guide 1-pitch to the right in the photo would decrease the overall string spacing and moving 1-pitch to the left would increase this.


The compensated increase in spacing can be seen in the example shown below by comparing the initial spacing (8.0mm) with the subsequent spacings ~ (the cumulative spacings being greater than multiples of 8mm). 

Slotting a guitar nut with compensated string spacing
Guitar nut string spacing with rule showing proportional increase

The spacing guide is removed and each string slot filed using the string action template as a guide to final depth.

Slotting a guitar nut with a gauged nut file
Adjusting the guitar string action at the nut
Checking the string slots for binding when slotting


The system can be used for 12 string guitars.


After marking the 1st group of six slots, the guide is then moved along to the next pitch (increased overall 'E' to 'E' on the guide) to mark the 2nd group of six.

The nut can be fine tuned in the jig with occasional reference to the instrument. Using an offcut of the same gauge will also assist this.

The nominal action achieved using the jig before any final adjustment on the guitar will be approx 0.020” (0.5mm). This is a general guide and will be subject  to other factors including the fret heights and string gauges.

Guitar Nut Shaping and Slotting Jig
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