Guitar Tech Tools – Essential or Extraneous?

When just starting out as a guitar tech you need tools, but which ones? Many newbies put their trust in places such as StewMac and buy things such as a notched straight-edge or a set of radius gauges.

But SM tools are pricey, and funds can be limited, especially when starting out. Buying one tool can mean having to pass on another tool. Do you need the notched straight-edge? What about the radius gauges?

According to StewMac’s product page for “Understring Radius Gauges”, they allow for “Fast, accurate bridge saddle adjustment”. Really? How?

SM doesn’t explain in writing but in the video, Erlewine states that “radius gauges are critical measuring tools..” and at about 0.28 in the accompanying video, he shows the radius gauge held over a bridge with six saddles and says that it is to be used during setup to ensure the saddles match the fretboard radius.


(Ok, excuse the outdated phrase and you’re free to Google it if needed.) I’m afraid D.E. may have sold his soul to SM. I hope he got a ton of money and that’s why StewMac has to charge us so much!

So here’s the problemS (yeah, I did capitalize that “S”!) with Erlewine’s “understring radius gauge” method.

  • It doesn’t include any measurement, nor even state a point from which to make such a measurement
  • It doesn’t allow having treble strings a bit lower than bass strings.
  • Fretboard radius is absolutely irrelevant for string height settings!* (You’ll see why in a moment!)
  • It is extremely difficult to accurately tell between two radius amounts, such as 14″ and 16″.
radius gauge for leveling frets
Frets on left have been crowned

The purpose of saddle height adjustment is to set your action (string heights) to a comfortable, yet buzz-free, heights. This means needing to measure the gap between the bottom of each string and the top of a particular fret – often the 12th fret, sometimes the 17th.

Usually, we’ll want the bass (wound) strings a tad (technical term!) higher than the treble (solid) strings. Since we measure directly beneath each string to the top of the fret, this automatically takes radius into account. But since we want slightly different heights for solid strings and wound strings, we do NOT want string bottoms to just follow the radius of the fretboard.

*Speaking of fretboard radius – the fretboard is irrelevant! That’s right. I said the fretboard radius does not matter. Why not? Well, do you know who did the last level/crown on this guitar? Are you sure he was a guitar tech guru?

It’s not uncommon for a tech to misjudge radius and, for instance, level crown frets to a 12″ radius on a 14″ fretboard. In such a case, if you then come back and level with a 14″ block, you’ll be taking too much material off the middle of the frets, likely making them wider in the center than toward the ends.

So it’s the radius of the frets, not the fretboard, that matters. But those silly radius gauges are not the answer!

You’ll feel like Mr. Magoo!

(Sorry again, younger folks – feel free to use Google again!)

One reason for mistakes is that these gauges are notoriously difficult to read accurately. I’ve often seen techs put a radius gauge on a fretboard, or on a fret, and confidently state, “That’s it – a ____” radius!” (Fill in with any number) Then, when asked to try another gauge amount, “Just to be sure.”, you get a long pause, a puzzled look, then he goes back and forth between the two gauges and ends with a big shoulder shrug!

Pic on right shows removing frets ->

Yes, I know to put a white index card behind the gauge or have a light at the far end, blah, blah. Those things are not very readable.

OK, so Google the radius. Ha! In my experience, the internet (even when on the manufacturer’s own website!) has an accuracy rating of about .600 – great for a baseball batter but not good enough to start filing a customer’s frets.

Goldilocks & the 3 Radius Blocks

radius blocks

So what’s the best way to figure the fret radius? Mark the tops of frets with a Sharpie, then take your best-guessed radius block and lightly go over the tops. If it took off ink just at the ends, it’s too sharp a radius, if the middle, then it’s too flat. If it gets middle and ends… then it’s just right!

What better way than to “measure” with the same tool that “needs to know” the radius?

Buy Or Pass?

They even want you to buy three sets of understring radius gauges to cover different situations. That adds up to over a hundred dollars. My verdict? (Betcha can guess!) It’s a hard pass for even one set! These things are useless and more likely to lead you to trouble than to be an aid.

Just this morning, I had a debate with a tech who has 14 years of experience about the usefulness or uselessness of a notched straight-edge. If you’d like to hear that one, I’ll post in a future blog rant.

hanks guitar shop
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