Hacklinger Caliper 1-12MM Measuring range 1 -12 mm.  Patented gauge for measuring the wall thickness of unopened instruments.  The small magnet is placed inside the instrument and allows measurements accurate to within 0.1mm.  The new version of this popular measuring tool features a wear-resistant rubber tip and 2 magnets to allow a greater measuring range.  Suitable for all non-metallic hollow forms like stringed instruments, pianos, containers, boats, ceramics, etc.  Includes instructions for use and leather case.