Trussrod for Music Man or similar. It works both ways. The disc-shaped nut (19 x 5.5 mm see photo) can be adjusted with a 4 mm Allen key or a 3 mm rod. Guitar model: 46.5x9x6mm Bass model: 61.5x9x6mm Always test the trussrod before assembling it, in case of breakage we can only replace the trussrod and not take on any damage resulting from the possible breakage of the trussrod itself