In a stator core assembly composed of a plurality of steel punchings, and a plurality of fastening devices including bolts holding the punchings together in a stack and pressing adjacent punchings against one another, the bolts being of a material having a coefficient of thermal expansion different from that of the steel punchings, the bolts are constituted by hollow tubes and the assembly further includes a temperature control device for introducing a fluid having a selected temperature to the interior of the tubes in order to minimize temperature dependent changes in the compressive force exerted by the fastening devices on the stack.