Identify the tool primarily used for measuring the thickness of aircraft materials.

The tool primarily used for measuring the thickness of aircraft materials is the micrometer. Micrometers are specifically designed for precise measurements, generally up to one-thousandth of a millimeter (0.001 mm) or one ten-thousandth of an inch (0.0001 in), which is essential when working with the materials used in aircraft construction and maintenance, where even minute differences in thickness can significantly affect performance and safety.

Micrometers have a calibrated scale that allows users to achieve highly accurate measurements and often come equipped with a depth gauge feature. This precision is crucial in fields like aerospace, where safety standards are strict, and material specifications must be adhered to meticulously.

In contrast, tools like tape measures and measuring wheels are better suited for larger dimensions, such as length and perimeter, and do not provide the same level of accuracy needed for assessing material thickness. Calipers are versatile and can measure internal and external dimensions as well as depth, but for the specific requirement of measuring thickness, micrometers are the preferred choice due to their high precision.