There are 2 different sizes for most U-joint applications. One is the standard 1310 series which is the smaller bearing and the 1350 ,which is bigger and used in most hi-po applications. They are also journals that have 1310 on one side and 1350 on the other depending on the end yoke on the rear and the yoke which is on the end of the driveshaft. Check out Dana/Spicer