This is an optional Yokomo Ventilated Dual Slipper Set. This advanced slipper provides YZ-2 and B-MAX2 series owners the option of a dual slipper design to provide smoother operation to help improve rear traction. In addition, the outerside plate has been finely crafted from aluminum alloy material to become a heat sink structure, enhancing the heat dissipation effect at the time of slipper clutch actuation.