Answer
The thrust capacity of a spiral retaining ring is usually limited by the shear strength of the groove material rather than the ring itself. The allowable thrust load $P_g$ is calculated using the formula $P_g = \frac{D d \pi \sigma_y}{K S F}$, where $D$ is the shaft/bore diameter, $d$ is the groove depth, $\sigma_y$ is the yield strength of the groove material, and $KSF$ is a safety factor (typically 2). For the ring itself, the shear capacity is $P_r = \frac{A \tau \pi}{K S F}$, where $A$ is the shear area and $\tau$ is the shear strength of the ring material. In soft materials like aluminum, the groove will almost always fail first by 'dishing' or deforming, which allows the ring to twist and pop out. Therefore, deepening the groove or using a harder housing material is more effective than using a thicker ring.
