These are the back fins (rear fins) for a quad fin setup. For changes in setup from a thruster to a quad, etc. Size M, brand new, unused. Thank you. #FCS2 #FCS #Performer #Surfing #Surfboard #Fin #QuadFin #QuadFin #Shortboard Accessories...Fins Type...Fins Fin System/Fin Box...FCS2 Number of Fins...Quad Fins Fin Material...Glass Flex Model Name...FCS II Performer