Set of varying (No.) degree Shims to alter your riding experience. Changing shims alters the amount of stabilising downforce provided by the tail, and also impacts the balance point of the foil and responsiveness.
Beginners should start with 1 or 2 and adjust based upon preference. Lower shim numbers allow faster speeds without too much front foot pressure, higher shim numbers create more stability and responsiveness, but lead to more lift at high speeds.