For 1990-2009 cars

Check thickness variation by measuring the rotor thickness at four or more points around the circumference of the rotor. Use a micrometer calibrated in centimeters (ten-thousandths of an inch). Make all measurements at the same distance in from the edge of the rotor.

Important: When refinishing brake rotors the maximum thickness variation should be no greater than 0.013 mm (0.0005 in).

A rotor that varies in thickness by more than 0.025 mm (0.001 in) can cause pedal pulsation and/or front end vibration during brake applications. A rotor that does not meet these specifications should be refinished to specifications or replaced.