TOOL
Action gauge
Reads string height at the twelfth fret without arguing about it.
| Range | 0 – 3 mm or 0 – 0.125 in |
|---|---|
| Graduations | 0.1 mm / 0.001 in |
| Material | Stainless steel or anodised aluminium |
| Features | Notches for string seating, fret slots marked |
| Size | Credit-card sized, pocketable |
| Reference marks | Common action targets printed on the card |
| Action at 12th | Electric 1.2 – 1.6 mm; acoustic 2.0 – 2.8 mm |
|---|---|
| Measurement point | Top of the fret to the bottom of the string |
| Fret state | Measure with relief already set |
| Repeatability | Take three readings and use the middle |
| Units | Record in one unit consistently |
| Price band | Low |
An action gauge is a graduated card or steel rule marked in the small increments action is actually set in — thousandths of an inch, or tenths of a millimetre. It sits on the fret and reads the gap under the string.
Setup targets are small enough that a general-purpose ruler is useless. Action at the twelfth fret for an electric is commonly 1.2 – 1.6 mm, and the difference between a guitar that plays easily and one that fights back lives inside that range.
At this stage
Action is measured after relief is set and the nut is cut. Measuring before either means measuring the wrong thing.
Suits these instruments
- All guitars and basses
Works with
- Feeler gauge
- Notched straightedge
- Truss rod
- Nut file set
- Slacken the strings before inserting a metal gauge under them if the gap is tight, so you do not scratch a fret or the underside of a string.
- Do not lever a gauge against a fret crown. It marks the fret.
Working notes
- Measure at the twelfth fret, between the two strings of a pair on a twelve-string.
- Write the numbers down. Setup is a sequence, and memory is unreliable.
- A gauge that reads in both millimetres and thousandths saves conversion mistakes.
- Check the action at the first fret with a feeler gauge as well — they are different adjustments.
Related
Feeler gauge
The only honest way to measure relief and nut height.
Notched straightedge
Reads the fretboard itself, not the tops of the frets.
String winder
Turns a fifteen-minute string change into five.
Capo
Clamps the strings at a fret — and shows up any setup problem.