The Hosco Groobar is a the perfect aid to help you cut nut slots. Simply choose your thickness, slide against the nut, and file away until you see marks in the groobar. That's when you know you've reached your desired depth. Never file your nut slot too deep again!
Sold in a set of 4 for Guitar
Features
https://youtu.be/XEpUi398_Fk