A: If you have a Jeep manufactured for use in the US or Canada, you will have a Dana 30 front axle.
Your rear axle will be either a Dana 35c or a Dana 44. To tell them apart, the Dana 35c has an oval shaped differential housing with a rubber fill plug on the differential cover. The Dana 44 has a 10 sided differential housing with a metal threaded fill plug on the diff cover. CLICK HERE TO SEE.
If you have A 2003 Rubicon, you have Dana 44 axles front and rear. (I HOPE you knew this already). The Dana 44 is the stronger of the 2 rear axles, but is available only on the Sahara and Sport as an option and as stated above, standard on the Rubicon. If serious off-roading with a locker or tires larger than 33", it is highly recommended to have the Dana 44 in the rear.