Answer
The thrust capacity of a spiral retaining ring assembly is fundamentally limited by the groove depth $d$. The formula for allowable thrust load based on groove deformation is $P_g = \frac{D d π σ_y}{S}$, where $D$ is the shaft/bore diameter, $d$ is the groove depth, and $\sigma_y$ is the yield strength of the groove material. Increasing $d$ increases capacity but also increases the stress on the ring during installation, as the ring must be expanded further to clear the shaft. Optimization involves finding the 'sweet spot' where $d$ is deep enough to provide a safety factor of $2$ against the applied axial load while ensuring the installation stress $\sigma_i = \frac{E t (D_{groove}-D_{free})}{D_{groove} D_{free}}$ does not cause the ring to set. For a 2-turn ring, the effective thickness $T$ is doubled, but the groove depth $d$ remains the primary constraint for the housing's integrity.
