The Pro Series II has the same strength as the original Pro Series, but is designed to give an alternative option to suit the needs of different applications and conditions such as mud and endurance racing. The Pro Series II features a sealed outboard CV with RCV's new accordion style boot made from high strength materials! Tests prove the Pro Series XP1000 rear axles to be 2 times stronger than the OEM shafts. Direct OEM fit replacement. 100% manufactured and assembled in the USA.