Guitar Neck Notched Straight Ruler - Made of stainless steel, rustproof, sturdy enough for your long-term use. Size: 16.5 x 1.45 x 0.15 inch, Dual scale design, works well with most guitar, specially suits for Gibson(24.75 inch ) and for Fender(25.5 inch ) electric guitars, pressed steel, may benefit from initial fettling,

The Neck Notched String Measurement Ruler is designed to check guitar neck straightness of the fretboard and frets. Fritz Ruler Use To Measure: Nut / String / Bridge / Pickup Pole Piece / Saddle Height Plus Saddle Slot/ Fret Slot Depths    
 

these are stamped steel 3mm thick and can need a slight straighten

now and again.