Chevrolet Repair: 1991 Corvette Rotors, rotor diameter, chevrolet corvette

Question
Hello,

I have a 1991 Chevrolet Corvette.  I need to replace all four rotors and I am ordering these parts from a catalog.  I was asked if I need 12 inch or 13 inch rotors.  I was also asked if I need these in the heavy duty option.  I do not know the answer to any of these.  The customer service representative states that the only way to really find out is to measure the rotor diameter.  Since I am not a mechanic, is there any other way to determine what type of rotors to order?  I did try to get the information through a local Chevrolet dealership parts department and I was told this information is not available through their department.

Answer
On the backside of the rotor under the rust there is a STAMPED part #. You can give them this number and they can cross reference it.

OR, You can remove one of the rotors and take it into any auto parts store and they can tell you by matching the rotor with their rotors that they have in stock.

QUESTION: WHY are you ordering them out of a catalogue ?.

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