The quad setup is four fins, two on each side, the fronts are typically larger than the rears but this is not always the case. The rears are nearly always inboard and aft of the fronts. This setup is relatively stable and is often used to provide more lift, control and speed. Some say adding a fourth fin is like add a nitrous booster to your rig. Perfect for performing speedy manuvers and great for the trickster.