The QD2 4.15 Blackstix is a large size quad rear with a Ride Number of 8.1. 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.