Official Answer
Answer
External spiral retaining rings are limited by their ability to 'cling' to the groove at high speeds. Centrifugal force causes the ring to expand radially. The speed $N$ at which the ring will lose its grip is given by $N = ± π \sqrt{\frac{E · g · (D_g - D_i)}{4 · ρ · R_m^3 · (1 + ν)}}$, where $E$ is the modulus, $g$ is gravity, $D_g$ is the groove diameter, $D_i$ is the free-ring ID, $ρ$ is the material density, $R_m$ is the mean radius, and $ν$ is Poisson's ratio. For high-speed applications, 'Self-Locking' features are used, where a tab on one turn locks into a slot on the other, mechanically preventing the ring from expanding. This allows the ring to operate at RPMs far exceeding the theoretical limit of a standard ring.
