| 摘要 |
A first outer surface is a convex surface, and constitutes a first cylindrical surface drawn by moving a first curved line defined on a flat surface P in the direction perpendicular to the flat surface P. A second outer surface is a concave surface and constitutes a second cylindrical surface drawn by moving a second curved line defined on the flat surface P in the direction perpendicular to the flat surface P. The second outer surface includes a pair of end areas drawn by moving the respective end portions of the second curved line and extending toward a middle side beyond the respective areas opposed to the seal, and a middle area drawn by moving the middle portion between the pair of end areas. The second support presses the pair of end areas, while avoiding the middle area.
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