PURPOSE: To prevent a foreign matter from entering into cooling medium, by superposing, on a bracket having an injecting hole as a through hole and a blind internally threaded hole, a packing having a projection to be inserted into the injecting hole and a plate, while fixing the packing and the plate to the bracket by means of the thread.

CONSTITUTION: A bracket 12 is provided with an injecting hole 12a consisting of a through hole and with a blind internally threaded hole 12b. A bracket 12 is further provided thereon with a silicon packing 13 having a projection 13a, which is inserted into the injecting hole 12a so as to seal the same. A metal plate 14 is further mounted on the silicon packing 13, and the metal plate 14 together with the silicon packing 13 are fixed to the bracket 12 by engaging an external thread with the internal thread 12b of the bracket 12. Since the injecting hole, which is a through hole, is not required to be engaged by the external thread 15, cut scraps of the bracket 12 can be completely prevented from entering into cooling medium.