We've already discussed what is a truss rod in another article, but did you know that there are two main types of truss rods -- single-action vs dual-action truss rods. So, let's find out more about them.
Single-Action Truss Rod
As the name suggests, single-action truss rods only function in one direction to balance the string tension and keep the neck straight. They are a simple design with a single piece of steel rod that is threaded on one end to receive an adjustment nut (which can be removed) and a washer. The other end has an anchor which needs to be installed in a curved channel. Unlike dual-action truss rods, they can only bend the neck backward.
Dual-Action Truss Rod
Double action rods, also known as 2-way rods, are typically made of a fixed flat bar and an adjustable round bar that are welded together with threads on both ends. To enable accurate adjustments, the adjustment nut is often welded to the end of the rod and can't be removed. They can not only counter string tension, but add to it. As you screw the nut of the truss rod, the round bar will bow backward to counter the tension of the strings, and as you loosen the nut, it goes back to the flat position.
Typically, a neck will be straight when there are no strings attached, and bow as the tension of the strings takes effect.. In this scenario, a single-action truss rod is all that is required. However, if you have a more rigid neck or are using thinner strings with less tension, the force exerted on the neck might not be enough. In this case, a double-action truss rod would be required to add the required tension.
