This document discloses an exhaust gas turbocharger, which includes a turbine disk connected to a turbine disk hub. The turbine disk hub extends distally away from the turbine disk and towards a shaft that connects the turbine disk to a compressor. The shaft includes a proximal end that includes a shaft hub that extends proximally away from the shaft and towards the turbine disk hub. The turbine disk hub is coaxially connected to the shaft hub at a joint. The turbine disk hub and the shaft hub form a cavity between the turbine disk and the proximal end of the shaft. The turbocharger also includes a sleeve having an inner surface that surrounds and engages at least part of the turbine disk hub, at least part of the shaft hub and that further surrounds the joint and partially surrounds the cavity. The sleeve provides structural reinforcement for the joint and additional cooling functions beyond the cooling function provided by the cavity.