| 摘要 |
A pair of similarly transversely bowed and superposed panel members are secured together and are V-shaped in plan. The apex portion of one panel member disposed to the concave side of the other panel member is sharpened and the panel members are secured together along their base edge portions with the remaining portions of the panel members disposed in slightly spaced apart relation. The opposing surfaces of the spaced apart portions of the panel members include coacting projections for frictionally clampingly engaging the portion of a flexible cover disposed to one side of a slit formed in the cover through which the aforementioned one panel member extends.
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