| 摘要 |
The hollow bar (1) has a U-shaped cross-section with its ends joined, giving it a curved outer face (5) and a flat inner face (4) to which horizontal members are fixed. It can be made from a metal such as steel or aluminium, composition or synthetic materials, and the flat face extends along its whole length. The cross-members (2) are of smaller section than the bar and are joined to it by welding in the case of metal or adhesive for the composition and synthetic materials.
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