Zipperfoot,,
5.O comes with 3.0 shafts. They are smaller than the previous 4.0. Most guys on clay liked the 4.0 shocks better than the 5.0 as it seems to handle better. Tlr came up with a conversion for the 5.0 shocks to make them the size of the previous 4.0 shocks. You could just run 4.0 shocks if you had some laying around to see which you like better. The advantage to the conversion kit is that you keep most of the parts of your current 5.0 shocks and just change the shaft and bodies. As someone above mentioned you keep the screw on pistons, lower collars, and locking bottom spring cups. Hope this helps. It was mentioned in the video that a lot of drivers prefer the current 5.0 shocks(3mm) for carpet but prefer the 5.0(3.5) conversion for high bite clay.