PURPOSE: To attain fixed sealing in the seated position of an annular metal plate part by providing a protruding part at the inner end part of a leg, turned in an axial direction, of the annular metal plate part provided with hermetic coating, and engaging this protruding part with a groove on the opposite side.

CONSTITUTION: A second metal plate ring 3 is provided with hermetic coating 6 at the peripheral surface of a leg 3' so as to attain airtight closeout to a shaft 5. In order to prevent the hermetic coating 6 from being scraped off at the time of assembling the metal plate ring 3, a radial protruding part 7 is integrally formed at the inner end part of the leg 3'. This protruding part 7 enlarges the diameter of the leg 3' provided with the hermetic coating 6 during assembly. The hermetic coating 6 is not pressed to the shaft 5 until the protruding part 7 is engaged with a groove 8 of the shaft 5, and the protruding part 7 closes a possible clearance depending on occasions. After the protruding part 7 is fitted into the grove 8, the metal plate ring 3 is axially fixed onto the shaft 5.