This grooved ring is the drive element inside the brake pump assembly. It transmits rotational force from the pump shaft to the piston mechanism that pressurizes the brake circuit. The ring sits on the pump shaft and engages with the internal bore of the pump housing; its grooves match the spline pattern of the original shaft so that torque is transferred without slippage. Wear on the ring teeth causes a loss of pump output pressure, leading to a soft or unresponsive brake pedal. As an original-manufacturer component, the ring is machined to the same spline geometry and hardness as the part it replaces, preserving the engagement depth and clearance that the pump relies on for consistent fluid displacement.