| 摘要 |
PROBLEM TO BE SOLVED: To provide a screw without tearing an opening hole even if weight of the whole board material increases by an external factor, by coping with flapping by releasing the extension-contraction of the board material without requiring labor of work when fastening the board material of an election poster billboard to a frame material. SOLUTION: This screw has the center in a shaft part at a predetermined interval further to the head part side from a head part side tail end part of a screw thread, and is parallel to a plane vertical to the screw axis, and has an annular projection having a diameter larger than an outer diameter of the screw thread. The annular projection forms a shape of converging an upper surface and an under surface for separating from a peripheral surface of the shaft part, and becomes a diameter smaller than an outer diameter of the shaft part at a predetermined interval further to the head part side in succession to the annular projection. An annular recessed part having its center in the shaft part is arranged up to a tapered part under a head part. COPYRIGHT: (C)2006,JPO&NCIPI
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