Turning Point's Hub Kit Systems are engineered to withstand typical wear and tear over time without risk of spinning or failure under normal operational use. Hub kits feature a unique patented one-piece hub with glass-filled nylon over brass splines to eliminate failures commonly seen in multi-part "sleeve and spline" designs and pressed-in rubber hub systems. Glass-reinforced high-tech polymer construction increases flexibility, eliminating potential stress fractures. High flow-through barrel exhaust system maximizes exhaust flow to increase horsepower and top end speed. Clear step-by-step instructions make installation easy. Turning Point's 500 series hub kits (for 4.25" and 4.75" gearcases) will upgrade and replace Mercury Flo-Torq II, Michigan Wheel XHS, and Solas Rubex hub kit systems. Propeller Housings are sold separately. MasterGuard 506 Hub Kit Only - 13 tooth spline. MasterGuard 506 Applications: Suzuki• 60 - 140 HP engines with 4.25" gearcase One-piece hub design Glass-reinforced polymer for flexibility Maximizes exhaust flow for more horsepower | MasterGuard 506 Propeller Exchangeable Hub Kit