Official Answer
Answer
A spiral retaining ring is designed to work against a sharp-cornered mating part. If the retained component has a large radius or chamfer at its base, it will contact the ring at a point further from the groove wall. This increases the 'lever arm' of the thrust load, creating a large bending moment that encourages the ring to 'dish' and fail. If a radius is unavoidable (e.g., due to stress concentrations on a shaft), a hardened 'back-up washer' with a sharp corner should be placed between the radiused part and the retaining ring. This ensures the load is transferred to the ring as close to the groove wall as possible, maximizing the shear capacity.
