Durango axle question - 8.25 vs 9.25

Looking at the Dodge web site, the 'build your Durango' part refers to a choice of a 'Corporate 8.25' vs. a 'Corporate 9.25 LD' rear axle. Can
someone explain? I know about gear ratios, but this is a separate item. Is it the size of the axle, and therefore the weight-bearing capacity?
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