Amtake Stainless Steel Guitar String Action Ruler Gauge Tool,Double Sided Multi Function Guitar Luthier Accurate String Measurement for Electric Bass and Acoustic Guitar Application: electric guitar, bass and acoustic guitar. Ruler size: 8.9 * 5.1cm / 3.5 * 2in (length * width) Scale for string height: 0.01-0.14in / 0.25-3.50mm Scale for bridge saddle slot depth: 0-0.875in / 0-20mm Scale for nuts saddles and polepieces: 0-0.75in / 0-20mm