taut to fully depress. Adjusting the action On some instruments, such as certain guitars, the action can be adjusted by tightening screws at the bridge, which changes the height of the strings. Tune-o-matic bridges use small thumbwheels for this purpose—sometimes accompanied or replaced by flat-head screw fittings. On other instruments, changing the action is more difficult, involving the removal of entire pieces from the instrument. On a typical steel string acoustic guitar, for example, the action is adjusted by carefully sanding the guitar's saddle so that the strings sit closer to the fretboard. The action on a guitar is also slightly affected by the adjustment of the truss rod. Tightening the truss rod bends the neck backwards, lowering the action—and loosening the rod lets the neck bow forward, raising the action. Action on a guitar is usually measured at the 12th fret. Typically preferred action on an electric guitar is around 1/16" (1.6mm) on the high E string and 3/32" (2.4mm) on the low E string when in standard tuning using standard gauge strings. Sometimes a straight neck works best for guitar action, but many luthiers and musicians favor a slight forward bow—called the relief—to reduce buzzing by accommodating the shape of a vibrating string. Adjustment to the action should be done using all the aforementioned truss adjustments, in addition to modifying or adjusting any elements on the bridge of the guitar. Truss rod access References Musical instruments