9: Non-destructive Examination

9.3.2.2 Mechanical Aids
a. Steel ruler—available in a wide selection of sizes and graduations to suit
the needs of the inspector (considered a non-precision measuring
instrument).
b. Vernier scale—a precision instrument, capable of measuring in decimal
units to a precision factor of 0.0001 in. The Vernier system is used on
various precision measuring instruments, such as the caliper, micrometer,
height and depth gages, gear tooth and protractors.
c. Combination square set—consisting of a blade and a set of three heads:
Square, Center and Protractor. Used universally in mechanical work for
assembly and layout examination.
d. Thickness gauge—commonly called a “Feeler” gauge is used to measure
the clearance between objects.
e. Levels—tools designed to prove if a plane or surface is truly horizontal or
vertical