The Futures Fins QD2 3.75 Quad Rears. If you're looking to turn your favorite Thruster set into a Quad, this pair of Quad Rears can be hooked up with any Futures front fins to suit your riding style, board design and conditions. With a symmetrical foil, these rear fins will suit smooth rail to rail surfing and speed, and will work best in boards that have the rear boxes set off the rail (closer to the stringer).