For 1990-2009 cars

Thickness variation can be checked by measuring the thickness of the rotor at 4 or more points around the circumference of the rotor. All measurements must be made at the same distance in from the edge of the rotor. Use a micrometer graduated in ten-thousandths of an inch (0.0001 in [0.002 mm]).

A rotor that varies in thickness by more than 0.013 mm (0.0005 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.