'01 Brake Help Please

I'm getting ready to replace the front brakes on my '01 XJ, but I'm kinda confused. I haven't had an opportunity to pick up a FSM yet. (I know, I know). Looking at different parts vendors online, there's a 3-1/16" height and a 3-3/16" height rotor for the front. One being cast and the other being composite. What determined which rotors were used? Do I have any options other then pulling off the rotor and measuring? I'd imagine it would be pretty obvious that a composite rotor looks different from a cast rotor, but having never seen one I don't know for sure.

Also, any online guides or tips to doing these? I'm good with this stuff, but considering this is my daily driver I don't want to risk getting stuck with no ride.

Take the rotor off to check, its not hard. The cast rotor has a thicker cross section at the bolt pattern, at least 1/4", whereas the composite rotor use a stamped sheetmetal part for that area and it is much thinner.

Hey, I just went thru this a couple weeks ago, I got a full cast rotor and it fits fine on my 98. Just go get it from carquest. I posted the part numbers back then too.