Adjustable truss rods are amazing. Seriously. They’re amazing. They allow us to tailor the neck relief to suit a player’s style. Without them, we’re more limited in what we can do during a setup (As an aside, while Vigier make great guitars, I’d happily give up all the carbon fibre solidness for the chance to tweak the truss rod when needed).
Hurrah for adjustable truss rods.
However, things haven’t always been like this.
In the very old days*, guitars had no truss rods at all. This wasn’t so much of a problem with gut strings but, once steel strings came along, a neck had to be huge to stand a chance of resisting their tension (and even then, most didn’t).
Builders realised that some sort of strengthening was required and so various things began to be inserted into guitar necks to help make them stronger.
The Early Days — Ebony Reinforcement
At its simplest, a square-section fillet of harder wood — say ebony — was inlaid along the centre of the neck, under the fingerboard. Martin Guitars began reinforcing their necks with ebony around 1920.
Better than nothing, but surely they could do better.
They got serious: Steel. Yeah! Nothing beats steel, right? But what’s it look like?
A while back, I realised I had a couple of Martin guitars of different vintages in for neck resets. So, with the necks off, I took a photo showing Martin’s different steel truss rods.
The Martin T-Bar Truss Rod
Starting in the 1934, Martin replaced the ebony strips out a T-shaped steel bar. Rumour has it, this bar stock had been originally used for blades on snow sleds.
It worked pretty well, too. Thumbs up for the T.
The War and The Return of Ebony
During World War II, steel was in shorter supply because it was being made into helmets and ships and ration tins and stuff for killing enemy soldiers. The ebony reinforcement made a comeback. It's all a bit hit-and-miss, though — some guitars still had T-bars and some had ebony. A magnet can be a useful thing to have with you if you're checking guitars of this vintage.
As the war shortages eased, the T pushed out ebony and reigned supreme for another twenty years or more. Until…
The Martin Square Steel Tube
Martin switched from T-bar to square steel tube truss rods in 1967.
That’s what everyone in the guitar world calls it; the ‘square tube’. It’s a length of ⅜” (9.5mm) square tubing (or ‘box section’.
Square tubing is lighter than using a solid square bar and still manages to remain pretty strong. That said, most consider that the square tube wasn’t as strong as the T-bar that preceded it. Dan Erlewine even has a clever trick for inserting a carbon rod inside the tube to give it some more strength — effectively reinforcing the reinforcement.
The Age of Adjustability
The square tube continued for almost twenty years. It’s only since 1985 that Martin have been installing adjustable truss rods across their range. While they arrived to the adjustable rod party relatively late compared to many manufacturers, at least they got there.
And that gets another ‘hurrah’ as far as I'm concerned.
It's Always More Complicated…
Even after the adjustable rod was pretty much standard across most Martin models, a few 'special order' models were still being made with the square tube. The world of guitars is rarely straightforward.
*I say ‘very’ old days because I’m mainly talking about Martin Guitars here. There were instruments made without any truss rods, or with rudimentary/token rods, much, much later. And yes, you could shoot arrows from many of them.