A micrometer is used to measure ________

A micrometer is an precision instrument designed to measure small dimensions with high accuracy. In the context of brake components and their specifications, it is particularly useful for measuring the thickness of rotors, which directly relates to safety and performance.

When measuring rotor thickness variation, a micrometer can provide accurate readings to ensure that the rotor maintains consistent thickness across its surface. This is crucial because variations can lead to issues such as uneven wear, vibrations, and brake performance problems. By using a micrometer, technicians can detect any deviations in thickness that may compromise the brake system's effectiveness.

In contrast, while a micrometer can indeed measure thickness accurately, it may not be the best tool for assessing rotor runout or caliper piston clearance, which involve different measurement techniques and tools more suited for those specific tasks. Likewise, measuring brake pad thickness is typically done using vernier calipers or specialized tools designed for pad measurement, as the dimensions and tolerances differ from those of a rotor. Thus, the primary application of a micrometer in this scenario is best represented by its ability to measure rotor thickness variation precisely.