<Li> On older Fender - style electric guitars with bolt - on necks (and vintage re-issues)--on the heel of the neck . Adjustment of such truss rods can be done by a Phillips screwdriver and requires prior removal of the guitar's pickguard or neck . </Li> <Li> On newer Fender - style electric guitars--behind the nut, uncovered and can usually be adjusted by a 1 / 8" (3 mm) Allen wrench . </Li> <Li> On set - neck electrics--under a cover - plate behind the nut . Gibson & Epiphone guitars have their truss rod bolt covered with a signature bell - shaped plate . Most Gibson electrics have a 5 / 16" (8 mm) or a 1 / 4" (6 mm) hex adjustable truss rod nut that can be adjusted with a hex box spanner wrench . </Li> <Li> On acoustic guitars--inside the guitar body, accessible through the sound hole, or on the headstock . Martins use a 3 / 16" (5 mm) Allen wrench and Gibson uses the same as for the Gibson electrics above . </Li>

How does a guitar neck truss rod work