Bass Neck Straight Edge (Notched) Luthiers Tool
This is the only true way to check for straightness before leveling your frets. Essential for proper truss rod adjustment. 1/8"x1.5"x23.5" Machined Edge 6061 Aluminum.  One side is for 34"(Fender) scale basses, and the other side is for 35" (most 5 string) scale basses.  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 for the neck . You can also place on top of the frets (off the cut notches) to use as a Standard Straightedge to check fret wear and level. If you're not sure scale length of your bass... measure from the edge of the nut (headstock) to the center of the 12th fret. It should be about 17" or 17.5" +/- 1/16"