Identify the causes of a retaining ring 'walking' out of its groove during operation.

'Walking' is a failure where the ring progressively moves out of the groove, often without the material actually breaking. The primary causes are: 1) High-frequency axial vibration that exceeds the ring's seated friction, 2) Impact or 'shock' loading that causes the ring to momentarily dish and lose grip, and 3) Excessive 'radiused' or 'chamfered' mating parts that apply a radial force component. To troubleshoot, engineers should check the squareness of the groove and the mating part, and consider increasing the ring's 'cling' by reducing the ring's manufactured ID for an external application.