Do I have Cast Iron or Composite rotors?

I am replacing the front wheel bearing on my 99 cherokee sport and there are 3 parts for it.. One of which I bought and installed because it was the only of the 3 they had in stock. It was for a composite setup and everything bolted on fine, but the length of the hub was shorter than the OEM part.

I spoke with Jeep and according to them, the only differernce in the 3 parts is the length of the hub. Not the diameter or the hub or anything like that.

So my main question is, there is 2 more parts available, one for composite and one for cast iron. How can I confirm which of the rotor types I have before I special order this part?

Thanks in advance for your help....

Don't forget to use the search function at the top of the page. This topic has come up before and somebody has posted a description of both types and some pictures.
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There were different unit bearings used in XJ's. 1984 - 1990 had a smaller wheel flange, 1991 - 2001 had a larger wheel flange. The '01 uses full cast, but at a different back spacing than the early style.
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http://www.naxja.org/forum/showthread.php?t=58865&highlight=composite+rotors