Everyone, or almost everyone, loves guitars. One way or another, they’re present in almost every genre. Combine this popularity with the fact that it’s not that hard to learn basic stuff on it, you’ll often see beginners taking up guitar as their first instrument. But when you get a guitar, be it an electric or an acoustic, you get some tools with it. So you may wonder, “Why did I get an Allen key with my guitar?

The first thing you need to know is that guitars evolved a lot since the first half of the 20th century. Be it acoustic or an electric one, they come with a neck that has a truss rod going through it. This is literally a metal rod that helps you keep your guitar’s neck straight. The tension caused by the strings, plus various other types of stress, tend to bend your guitar’s neck in one direction.

So what does that have to do with this Allen key that you got with your guitar? Well, the Allen key that you got, or hex key, is there to help you set the truss rod. This way, you can keep your guitar’s neck completely straight.

Additionally, electric guitars also come with a smaller Allen key. Well, at least some guitars.

Look, if you’re a beginner, all of this probably seems a bit confusing to you. Why do you need an Allen key? Why do some electric guitars come with an additional smaller Allen key? We’ll get to all of this and clear things up for you.

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What is the Allen Wrench for on a Guitar?

So‚Ķ What’s it for and how do you actually use it? As I’ve already mentioned, almost exclusively, all guitars today come with a truss rod. In some cases, we even have dual-action truss rods, but we’ll get to that.

Truss Rod

If we’re talking about acoustic guitars, you can find one end of the truss beneath the soundhole, on the side that’s facing the instrument’s neck. If you look closely, you’ll see what looks like a top of a screw. But instead of a regular screw, you see a hexagon-shaped indent, usually about 5 millimeters in diameter. This is where you’ll want to use the Allen key that came with your acoustic guitar. However, it’s important to note that classical nylon-string guitars don’t come with a truss rod.

As for electric guitars, the main end of the truss rod is located at the headstock. It can either be uncovered, where you see the hole with the screw head, or it can be hidden behind a plastic cover. Electric guitars usually feature truss rods that are adjusted using a 1/8-inch Allen key. There are also some other examples, although they’re not as common.

Dual-action Truss Rod

More expensive and prestigious electric guitars can come with so-called dual-action truss rods. What this means is that the metal rod going is adjustable on both of its ends. This allows for a much more detailed setup and it’s usually present on guitars that are designed to work with super-low string action. They’re not that common, but can be useful for such a setting.

If you’re playing an average mid to high-priced electric guitar, there’s a high chance that you won’t need it. There are some acoustic guitars with dual-action truss rods, but they’re even less common than electric guitars with the same kind of setting.

Gibson Truss Rods

Gibson is one of those brands that prefer (for better or for worse) to be different than everyone else. This also goes for their truss rods. But instead of female ends, they have male ones. This means that they’re adjusted with a hex box spanner wrench instead of a hex key (a.k.a. the Allen key). These wrenches are usually made by Gibson and they basically look like pipes.

Instead of the standard 1/8-inch diameter, these come with a very specific measure, 5/16 of an inch. In some cases, Gibson truss rods come with a hex screw that is 1/4 of an inch. Either way, you’ll need to have this kind of a wrench if you own a Gibson guitar. As someone who plays a Gibson Les Paul, I can safely say that this is yet another unnecessary cost of owning a Gibson guitar.


Additionally, hard-tail bridges or Fender-style bridges on guitars also come with screws that are adjusted using an Allen key. However, these are much smaller in diameter and are in most cases 0.05 inches, which is 1.27 millimeters.

If we’re talking about Fender-style bridges, be it tremolo or hard-tail ones, you can notice two individual screws on each saddle. For those who don’t know, the “saddle” here is the metal block on the bridge that holds each individual string. Screws are located left and right of each string and you can adjust them with these small Allen keys. In this case, adjusting saddles is all about string height or string action.

Floyd Rose bridges, or any similar types, don’t have these screws that are adjusted using small 0.05-inch Allen keys. Instead, they require two types of Allen keys. One is 2.5 millimeters in diameters and it’s used for the saddle-mounting screws. The other one, which is 3 millimeters in diameter, is for the string clamps and other similar components. Setting up a Floyd Rose or a Floyd Rose-style bridge is a story of its own. And, according to Floyd Rose users, it’s kind of a nightmare, but that’s a whole different topic.

Tune-o-matic Bridges

As far as tune-o-matic bridges go, they feature no components that are adjusted using Allen keys. Instead, you just need two flat-head screwdrivers, one smaller and one larger, and some patience. If you bought a guitar with a tune-o-matic bridge, you’ll just get an Allen key for the truss rod.

Why Do Guitar Necks Bend Over Time?

All guitars are susceptible to their environments and various factors. Strings pull the neck towards the body over time. Knowing that wood is flexible, it can warp over time due to this pressure.

Electric guitar neck

On the other hand, if your strings are too loose, or if you keep your guitar standing without stings for too long, the neck can go the other way.

Additionally, both acoustic and electric guitar necks are sensitive to temperature changes and moisture. This is especially noticeable in substantially arid or wet areas. While you should also find ways to keep your guitar safe from these external factors, adjusting a truss rod after a while is a must.

How Truss Rods Work

A truss rod goes through an entire length of a neck. In most cases, the truss rod gets loose. In order to turn it back into a straight position, the truss rod screw should be turned clockwise. If it’s too tight, meaning that the neck has a concave shape, then you’re supposed to turn it counterclockwise.

However, adjusting a truss rod is something you need to be careful with. You’re supposed to make very small turns and check what’s going on with each turn. It’s tricky, but it gets easier with experience.

Setting Up Your Truss Rod: What You Need to Know

So let’s see how you’re supposed to set a truss rod. These rules apply to both acoustic and electric guitars, as well as different types of truss rod screws, standard or the Gibson type.

While the perfect setting requires a specialized bench, you can improvise a little. You’ll need a flat surface and a blanket or a towel, something soft to cover this hard surface. Lay your guitar onto it, and if you have a guitar with an angled headstock (like standard Gibson guitars), make sure that the headstock is hanging from the surface. You don’t want to lay it on the same surface as the body since it can potentially damage your guitar’s headstock or neck.

Next up, you’ll be doing the “tap test.” Press the 1st fret with your fretting hand or a capo and the fret near the body and neck joint with the pinky finger of your picking hand. Then, with any of the index fingers that are available, press the bottom string right in the middle of these two points.

If you feel that there’s a lot of space between the string and the fret, then your neck is forward-bowed. If there’s not much space, or if the string is already pressed against the fret, then the neck is back-bowed.

Forward-bowed or relieved necks need some tightening up. Necks that are too tight, or back-bowed, need to be loosened up. It’s as simple as that.

Keeping Your Guitar Safe

But despite all of this, you should always keep your guitar safe. This goes for factors like temperature, humidity, and proper placing. Controlling humidity levels is easy with today’s tool, which includes different types of humidity control systems. If you’re living in extremely arid or wet areas, these can save your instrument in the long run.

As for the placing, it’s important to put your guitar on proper guitar stands. This means that the instrument’s weight should never be supported on its neck. The only exception is when you’re using wall-mounts, which are designed to safely hold the instrument to its headstock, but the whole weight pulls straight down.