Final answer:
The splined sleeve is the component internally splined to match external splines on a transmission or transfer case's output shaft, enabling torque transfer within a vehicle's drivetrain.
Step-by-step explanation:
The component that is internally splined to fit with external splines on the output shaft of a transmission or transfer case is the d) Splined Sleeve. Splined sleeves are used to join together two rotating shafts within a mechanical system. These sleeves are designed with internal splines that match the external splines on a shaft, allowing for a precise fit that can transmit torque effectively. This connection facilitates the transfer of power through the drivetrain in vehicles, from the transmission to the wheels or from the transfer case to the axles in four-wheel-drive systems.