| 摘要 |
To ensure positive inter-engagement of the free edge of a male rib at one side of a roof or wall cladding sheet with an internal shoulder formed in, and longitudinally of, a female rib at one side of an identical sheet, the said free edge has a series of outwardly displaced abutments formed on it so that engagement between the two is confined to those points at which the abutments are placed.
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