Designed to check bass guitar neck straightness of the fretboard and not just the frets. This is the only true way to check for straightness before leveling your frets. Essential for proper truss rod adjustment. 1/8″x1.5″x23.25″ Machined Edge 6061 Aluminum. This is very rigid and will last for years without bending. One side is for 33 ¼” scale for standard Rickenbacker basses(4001-4003 and more), the other side is a standard straight edge machined flat with no fret notches.* CNC precision machined for a flatness of +/- .001″ Good to use with 18 or 20 fret necks..doesn’t matter. Use with strings on or off. Notched to the 19th fret with clearance for more frets and clearance for the nut on the other end. Covers the entire length of the neck . *Will not work with short scale basses.