There are actually seven u-joints on our TJs, two on the axle shafts and five on the front / rear driveshafts.
Two front axle shaft u-joints:
The factory u-joint on standard (non Rubicon models) is a Spicer 5-297. A highly recommended upgrade is the
Spicer 5-760x u-joint which was specially designed for the Rubicon at Jeep's request.
Driveshaft u-joints:
The stock driveshaft u-joints are Spicer 1310. There are three u-joints up front and two in the rear. A highly recommended upgrade is the
Spicer 5-1310x which is sealed, as well as a stronger and more durable directly replacement upgrade for the standard Spicer 1310 size u-joint.
Notes:
The TJ Rubicon uses different driveshaft u-joints and I'll have to recompile my list of those since they vary between 2003-2004 and 2005-2006 Rubicons. All years of the TJ Rubicon came standard with the
Spicer 5-760x front axle shaft u-joints.