Flexible Couplings consist of a contoured flexible disc moulded in tough yet resilient new type polyurethane. The contoured disc gives clearance for the bolt heads, and is able to flex freely to take up any temporary misalignment of the engine and shaft, due to flexing of the boat structure or the engine moving on its rubber vibration isolation mountings. Flexible couplings install simply and quickly, No cutting or machining is required. And, you don't have to haul your boat out of the water. just separate the drive flanges, insert the coupling, align coupling and bolt together.