Ultra high rebound urethane formula. Sets of bushings and washers. The bottom bushing provides stability, the top bushing provides deck lean / turnability.
Replace your stock truck bushings for your preferred performance. Hardness is measured in durometer, with the softest bushing being 88A, going up to the hardest bushing, 96A.
Soft - Easier turns, big carving
Hard - Stiffer turns, great for larger / heavier riders to prevent wheel bite
Medium - In - between. A great place to start if you don't have a preference.