From Team Associated:
This new top shaft screw replaces the stock steel version found in the B6.1, B6.1D, T6.1, and SC6.1 Team Kits. It reduces the rotating weight and comes with preinstalled pin for easy assembly.
Compatible with layback, laydown, and standup gearboxes when using the slipper clutch. Weighs 40% less than the stock steel screw.