Hygear dual rate spring kit for and Ski-Doo REV snowmobile with SC-4 rear suspension. I used this on a 2005 MX Z X 800 and it worked for better than stock setup especially if you ride rough trails. 

Comes complete with spring spacer and crossover rings to adjust when it changes from one spring to two. 

The main spring is 6" long and .350" wire diameter.

The tender (shorter) spring is 2.5" long, gray in color with white stripe and .288" wire diameter.

The black ring in pics goes between the two springs.

This spring kit will fit your stock center shock or aftermarket shock as well.

Hygear part #30-11-003S. Hygear cost $149.99