Futures Fins QD2 4.0 Blackstix Quad RearsQD2 4. 0 Blackstix Quad Rears The QD2 4. 0 Blackstix is a medium size quad rear with a Ride Number of 8. 2. Looking to turn your favorite Thruster set into a Quad? This pair of Quad Rears can be combined with any Futures front fins to suit your riding preference, board design and waves. With an 80 20 foil, these rears are a mix of response and control. They will favor boards that have the rear boxes set closer to the rail, away from the stringer.