Which tool can be used to check for rotor thickness variation?

The dial indicator is the appropriate tool for checking for rotor thickness variation because it measures the runout, or deviation, of the rotor's surface as it spins. This tool uses a probe that makes contact with the surface of the rotor; as the rotor rotates, any variation in its surface will cause the dial indicator's needle to move. This precise measurement allows a technician to identify discrepancies in rotor thickness or flatness that could lead to brake issues, such as vibration or uneven wear.

Other tools mentioned, such as a caliper gauge and a micrometer, are more suited for general thickness measurements rather than assessing variations over the surface area. A torque wrench, while essential for applying the correct amount of force during installation, does not measure rotor thickness or variations, making it unsuitable for this specific checking task.