Official Answer
Answer
A scalloped groove is a design modification where the bore leading to the groove is slightly tapered or features intermittent recesses. This allows the spiral ring to be compressed more easily as it travels down the bore. For internal rings, the ring must be 'wound down' to a smaller diameter than the bore. The scalloped design reduces the friction $F_f = \mu \cdot F_n$ between the ring and the bore wall, preventing the ring from scratching the honed surface of a hydraulic cylinder during the installation stroke.
