| 摘要 |
A tube 2 is composed of a first plate 6 and a second plate 7 which are opposed and engaged with each other. In a region C on both end sides of the tube 2 , the first plate 6 is formed into a shape in which an edge portion 6 a of the first plate is laid along a bent portion 7 b of the second plate so that an outer wall face of the tube will be composed of continuous face. In a region D except for both end sides of the tube 2 , the first plate 6 is formed into a shape in which the edge portion 6 a of the first plate 6 is laid between the edge portion 7 a of the second plate 7 and the bent portion 7 b.
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