A driving mechanism is disclosed particularly for use in advancing work pieces in the interior of a vacuum furnace, the mechanism extending through the furnace wall for motor or manual driving from the exterior of the furnace, the mechanism being replaceable as a unit, having provisions for sealing against fluid leakage and for reduction of heat conductivity between hot and cold locations, for liquid cooling at intermediate locations and for effective heat conductivity at cool locations. Provisions are also made for easy separation if desired of portions subjected to seizure at high heat levels, and for evacuation of interior portions subjected to vacuum.