Mercury - Flo-Torq SSR HD Propeller Hub Kit High-Performance Prop System Precision Marine Construction 8M0101603. Overview. When you run a powerful Mercury fourstroke in the 200 to 400 horsepower range, small details start to matter in a big way. You feel every vibration, every change in water texture, every shift of the prop as it loads and unloads. That is why the Flo-Torq SSR HD Hub Kit 8M0101603 feels like such a welcome upgrade. It brings calm to the chaos, smoothing out the transitions tha