Hi, I just acquired and old electric guitar apparently in decent shape. This guitar had apparently been sitting unstrung for several years. First thing I wanted to do was check to see how level the frets are. I checked the neck for straightness and found it had quite a bit of back bow. I loosened the truss rod, counter clock wise, a little at a time letting the neck sit for a few minutes between adjustments. Eventually I reached a point where the truss rod adjusting screw loosened up. The neck still had back bow so for the heck of it I gave the adjusting screw an addition 1/4 turn counter clockwise at which point I checked the back bow again and it appeared to be reduced even further. I stopped at this point because I didn't want to damage anything. I looked truss rods up on line was reminded there are both single and duel action truss rods. I had assumed this guitar would have a single action truss rod but now I'm not so sure. Are single action rods still in common use today and if so how can I be certain of which type, single or duel, is in this particular neck before proceeding further?