A cover is mounted to a heat-generating electronic part (T) for electrical insulation and heat dissipation purposes. The cover comprises a hollow cover body (20) of rectangular prism shape having a top wall (23), bottom wall (24), side walls, open front wall (21) and closed rear wall (22) and defining a hollow interior (27) into which the electronic part (T) is to be inserted. The interior has sufficient dimensions to accommodate the electronic part. The top and bottom walls are formed flat for slidable contact with the electronic part. The bottom wall is at least 0.1 mm thicker than the top wall.