Abstract: A C-shaped retaining ring having an open portion and at least two pairs of cutouts formed in the inner peripheral edge or outer peripheral edge of the ring and arranged symmetrically on the opposite sides of the open portion, the ring being uniform in its width and thickness circumferentially thereof. The cutouts are arranged at apexes of an equilateral polygon formed when the ring is loaded as installed on a shaft or in a bore. In addition, the cutouts are separately spaced apart along the peripheral edge of the ring and have a progressively increasing depth toward the open portion. The remaining width of the portion of the ring defining each of the cutouts satisfies the equation: ##EQU1## where b.sub.n is the remaining width, b is the width of the ring, .alpha. is the angle between the center line and the end face of the open portion, and .PSI. is the angle between the center line and the cutout.