FCS II Mayhem Tri Fins The MB template offers freedom to perform tight turns in the pocket with an emphasis on speed. Sitting in the reactor family, the MB is considered a high performance fin because it responds incredibly fast, but still offers enough control so you can confidently lay into a turn with plenty of force. Ideal Conditions A wide range of conditions, particularly good in critical overhead waves. Board Types Designed to fit the FCS II Fin System. Performance shortboards and hybrid models. Fin Family Reactor: Find Speed. Speed, tight turns & snaps. Sizing Medium (65Kg - 80Kg / 145 - 175 Lbs) Large (75Kg - 90Kg / 165 - 200 Lbs)