Contrast the impact of a 'Sharp-Cornered' groove versus a 'Radiused' groove on ring stability.

A sharp-cornered groove (maximum radius of $0.005$ inch) is ideal for spiral retaining rings because it provides a solid vertical ledge that prevents the ring from 'rolling' or 'dishing' under load. If the groove has a large radius, the ring will contact the radius rather than the flat wall, creating a wedge effect. This pushes the ring radially outward and induces a twisting moment. If a radius is necessary for shaft fatigue strength, a 'back-up washer' should be used between the ring and the radiused component to provide a flat mating surface.