Official Answer
Answer
Spiral retaining rings often include a small notch at the end to facilitate removal with a screwdriver. In high-speed turbomachinery (e.g., turbochargers), this small mass imbalance can lead to significant vibration. To counteract this, engineers can specify a 'balanced' ring, which adds a compensating mass or a second notch $180^{\circ}$ from the first. The centrifugal force $F_c = m \cdot r \cdot \omega^2$ must be calculated for the notch volume, and the assembly must be dynamically balanced after the ring is installed to ensure G-grade compliance.
