Answer
The thrust capacity of a spiral retaining ring is limited by two factors: the shear strength of the ring and the deformation of the groove. The shear-limited thrust $P_r$ is calculated as $P_r = \frac{D T \pi au_s}{K_s}$, where $D$ is the shaft/bore diameter, $T$ is the ring thickness, $ au_s$ is the shear strength of the material (typically taken as $0.6 \times \sigma_{tensile}$), and $K_s$ is a safety factor (usually 3). However, in many cases, the groove material (often aluminum or soft steel) yields before the ring shears. The groove-limited thrust $P_g$ is $P_g = \frac{D d \pi au_y}{K_s}$, where $d$ is the groove depth and $ au_y$ is the yield strength of the groove material. Designers must take the lower of these two values as the assembly's safe thrust capacity.
