Khiro barrel cup washers (set of 2)

These washers are sold per two. For two trucks you need four washers. Depending on the model of your bushings you need large (barrel shaped) or small (cone shape) cup washers.

Cup washers allow for the bushing to perform how they were meant to be. The cup washer restricts the bushing just enough in order to increase the rebound. 

Use the cupped washer on the board side and on the road side.

Barrel Bushings are cylinder-shaped. 
Cone Bushings are... cone shaped!