This is an optional set of Team Associated  12mm Rear Spring,blue, 2.30 lb

 
Team Associated's new Factory Team 12mm springs offer top level quality and precision by design. Through rigorous testing our engineers found that a spring with more coils for a given spring rate improves rate tolerances, and proved to be better on the track. The springs are also black oxide coated to reduce corrosion without affecting rate tolerances. Available in two universal lengths. By using different offset spring cups, you can obtain your desired ride height on all platforms with the same front or rear springs (No more truck and buggy sizes).
 
Big Bore Rear Spring Rates:
ASC91335 - 12mm Rear Spring (Black/1.90lbs)
ASC91336 - 12mm Rear Spring (Green/2.00lbs)
ASC91337 - 12mm Rear Spring (White/2.10lbs)
ASC91338 - 12mm Rear Spring (Gray/2.20lbs)
ASC91339 - 12mm Rear Spring (Blue/2.30lbs)
ASC91340 - 12mm Rear Spring (Yellow/2.40lbs)