Leaf Spring Shackle Spring/Shackle Bushing Spring/Shackle Bushing Kit. Black. Front And Rear Main Eyes. FEATURES: Premium Grade Polyurethane Components Precision Fabrication Assures Perfect Fit. PROTHANE Motion Control has become synonymous with innovative, hi-performance polyurethane or urethane for short, based bushings and driveline components. From bushing, bump stops and body mounts to stressed driveline components like motor and transmission mounts and lift kits, PROTHANE engineers are constantly developing innovative new hi-performance polyurethane based parts. As enthusiasts and racers, we take great pride in being the first to bring you better polyurethane bushings, transmission and motor mounts to enhance the performance of your vehicle.