Nut file

A narrow abrasive file ground to the exact width and profile of a string gauge, used for cutting or deepening nut slots.

Using an undersized file produces a slot that pinches the string, and an oversized one makes it rattle; a set of files in graduated sizes is the normal way to keep the slot matched to the gauge. The cut must also slope down towards the headstock, so the string bears on the front edge of the nut and the break angle is right. Because the amount removed is small and irreversible, the work is done a little at a time with the string rechecked constantly.

Example: a nut slot cut a hair too low will buzz on the open string and cannot be undone without filling and recutting the slot.

Nut file

See also