| 摘要 |
PROBLEM TO BE SOLVED: To provide bolt head fall preventing structure for preventing the fall of a bolt, head, even if a bolt is broken, thereby maintaining the soundness of a structure and preventing the hindrance of operation of a device and a plant. SOLUTION: This bolt head fall preventing structure is provided with a flange part provided projecting at the lower part of the bolt head; an annular flare part formed thin at the outer periphery of the flange part and turned upward; a counterbore provided a the upper part of a bolt hole to allow the bolt head to recede therein; a sidewall groove of a side wall of the counterbore provided having a larger inner diameter than the outer diameter of the flange part, at the side of the flare part, up to the height of the flare part of the fastened bolt or slightly higher; and an upper edge projecting from the upper end of the side wall, with a step on the inside of the counterbore. In the fastened state of the bolt, the flare part is fitted into the sidewall groove so as to engage the upper end of the flare part with the upper edge, and to hold the bolt head in the counterbore.
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