Official Answer
Answer
For a spiral retaining ring to reach its rated thrust capacity, the groove wall must be as square as possible (maximum $90^{\circ} + 0.5^{\circ}$). If the groove wall is 'radiused' or 'chamfered' due to improper machining, the ring will have a tendency to slide up the wall under axial load, inducing a radial force component that can cause the ring to expand and 'pop out.' According to Smalley's engineering guidelines, the maximum allowable radius at the bottom of the groove is typically $10\%$ of the ring thickness. If a large radius is required for shaft fatigue strength, a backing washer must be used between the ring and the radiused corner to provide a square seating surface.
