Truss Rod Screw Drivers
All modern electric and acoustic guitars have truss rods inlayed in their necks. Truss rods were developed over 60 years ago to help reinforce guitar necks and keep them straight. Over time due to environmental conditions, guitar necks can warp or bow. The truss rod helps correct this natural tendency. Basically it's a rod that is inlayed down the center of the guitar neck. When pressure is applied to the truss rod, tightening the truss rod, the truss rod bends inside the neck forcing the neck to bend with it. Loosening or tightening the truss rod will bend the neck in the proper direction to keep it straight. Generally speaking, the straighter the neck the more comfortable the guitar is to play.
Truss rods come in all different shapes and sizes, so do their access points. They have all different types of ends. The most common ends can be adjusted with screwdrivers, allen wrenches, and nut drivers. Some truss rods can be access through the truss where the fretboard ends. Others can be accessed at the bottom of the neck where the neck and body meet. Still other odd truss rods must be accessed through a back panel on the back of the guitar.
That is why there is no all-purpose truss rod adjustment tool. You will need a kit of truss rod tools if you plan on adjust many different guitars. Many guitars require a screw driver to adjust the truss rod. Fender Telecasters are a great example. The Tele access point is in the bottom of the neck. You will notice that half of the screw head is covered by the guitar body. In order to access the truss rod, you will have to unscrew the neck screws. Since it's a huge pain to have to take the entire neck off to adjust the truss then put the neck back on, test it, and probably take if back off. To save time, you can unscrew them half way and just tilt the neck back until the screw head is visible. This is where you need your screw driver. It is important to use a special screw driver to adjust this truss rod. Normal screw drivers flare out toward the end. These flares can dent the body. Either you need to get a special straight screw driver or you need to file down a normal one. Either one of these options will work.
You will also need screw drivers to remove truss rod covers and loosen neck screws. There are so many uses for a full set of screw drivers. You can't afford not to have a set. I would try to sell you on a set of screw drivers, but I think it is pretty obvious that you have to have a set in your guitar repair bench. So many repairs require screw drives that you can't really do much without them. Go pick up a set if you don't have one. If you would like more information about how to adjust your guitar truss rod, please see my truss rod adjustment article.