The stock Dana 30 axleshafts use Spicer 5-260X (left) while the Superior axles come with Spicer 5-297X U-joints. The difference in cap diameter is 1.063 inches versus 1.188, which may not sound like much. The real strength difference is in the larger diameter of the trunnions and cross-shafts. They offer both the sealed type and those with grease fittings. There are plenty of opinions on strength versus longevity, so you can choose which ever you want.