These are truss rod adjustments. Stings that are made from steel will exert a greater force on the neck, pulling it forwards. Tightening A Truss Rod (Righty Tighty) If a neck has too much relief (upward bow) tightening the truss rod will straighten the neck. NEVER adjust the truss rod in order to lower the strings. We need truss rods for instruments that have steel strings. The truss rod is actually compressing the neck exerting pressure against the backside of the neck which causes it to bend backwards. Loosening A Truss Rod Whichever setup you prefer, a straight neck is a good starting point. A little truss rod adjustment goes a long way, as you can see by measuring your string height before and after with a string action … A truss rod runs the length of the neck and is located underneath the fretboard. This technique is useful because it eliminates the bridge and nut (the overall string height, or action) from the equation and lets you look only at the shape of the neck. This is why, in the 1980s, double-action truss rods began to be used widely. Turn it about an eighth or quarter of a turn at a time and observe what happens to this string/fret relationship. Which Way Do I Turn? The majority of string height adjustment is done at the bridge on either the bridge posts or individual saddles depending on your guitar. With a properly functioning truss rod, you probably won’t need more than 1/8-turn in either direction to get what you’re after. The order is important because adjusting the truss rod will affect the action at both the nut and the saddle. However, with a one-way truss rod, if the neck warps away from the string pull, no amount of loosening the truss rod will pull the neck straight, because the truss rod only works against the pull of the strings. Most truss rods have a nut at one or both ends of the neck which we can use to adjust the tension on the neck. How? IF your truss rod is NOTadjusted correctly and is not countering the string pressure enough; it's too loose, your action will be lowered a little by properly adjusting the rod. BUT if it has the right tension for the strings you are using, you will have to lower the action by removing the saddle and sanding it down to the right height. The truss rod is there to do one thing—to keep the neck of your guitar straight and stable, keeping your instrument in tune all the way up its well-aligned neck. In turn, adjusting the nut will affect the action at the saddle.