To reduce the number of components and facilitate attachment with light weight, without sacrificing sealing property, by using a soft different thermoplastic elastic body which can be integrated with cured resin of a main body part by thermal fusion bonding, in an attachment part.

A main body part 2 is composed of hard synthetic resin, and constitutes an almost converging column which has a flange part 3 in the middle part. From the lower surface of the flange part 3 to the lower part of the main body part 2, an attachment part 5 is formed. The part 5 is formed integrally with the part 2 by thermal fusion bonding of thermoplastic elastic body which is softer than synthetic resin of the part 2 and different from the resin. The seal part of the attachment part 5 including a protruding part 5a for improving the sealing property to a seating face, a protruding part 5c for sealing the pressure of cooling liquid, and a protruding part 5b for bracing which is formed in the middle part. The protruding parts 5a-5c are forcedly inserted and crashed, so that sealing force is increased. In particular, the protruding part 5 is caught in the aperature of a fixing hole 9 and has the effect for preventing coming-out.