The Fouruster, compared to the standard  quad fin placing, has the rear fins moved to the tail and  off the rail towards the centre of the board. More like a thruster with two tail fins, than a quad ...advantages are that  they surf tight around the pocket, and because the fins are not triangulated, they're free to surf out on the face. Typically the rear fins are quite smaller. Suggested fins sizes would be the CGB Quads