Eria,

Those aftermarket car parts stores like AutoZone and the like may be misunderstanding the style of Montero Sport you have. Mitsubishi made 2 different LS styles in 2000; The LS and the LS 4WD model. You should make sure to be very specific when ordering. The rotors on the LS 4WD model are probably bigger than the LS model. Mitsubishi also made an XLS style. The parts store may be getting those models confused, and assume they are interchangeable.

Now, you didn't specify whether you're replacing your front rotors, rear rotors, or both. The rear rotors for just about every vehicle are smaller than the front. Those part stores maybe assuming your just replacing the rear, so they send you smaller rotors than you're expecting.

And it is possible they are sending you the correct rotors for your car as to their knowledge. Mitsubishi could have supplied incorrect cross-reference numbers to the major parts store. There are a lot of 'maybes' and 'if's' in this situation.

If you want to be absolutely positive you're gettting the correct sized rotors, write down your VIN number, call your local Mitsubishi dealership and ask them for the part numbers for the rotors you need. The parts department at dealerships usually ask for the VIN so they can be sure of the exact model and style of the your car. You can either purchase the rotors right from the dealership (which can be pricey) or use the part numbers they give you to cross-reference them with the aftermarket parts from the AutoZone stores.

I hope this was helpful. Good Luck!