| 摘要 |
PROBLEM TO BE SOLVED: To secure enough strength of locking a lower side plate W1 of work W with a piercing nut 1, driven into the work W comprising double-layered plates W1 and W2; in the bottom of the pierce nut, an inner cylinder 1b concentric with the screw hole 1a and an outer cylinder 1d, shorter than the inner cylinder 1b, are provided to form an annular groove 1c in between, and the inner cylinder 1b has a tapered periphery for larger outer diameter downward. SOLUTION: An inner volume of the annular groove 1c, located above the bottom of the outer cylinder 1d, is set to be larger than the volume of the work W pushed into the groove 1c, so that a pushed-in portion W1a of the lower plate W1, is completely taken into the annular groove 1c. In addition, the inner periphery of the outer cylinder 1d is formed to be concaved more outward than its lowermost periphery non-cylindrically, so that, the part of the outer corner portion W1c of the pushed-in portion W1a of the lower plate W1, is further extended radially by the outward drift by caulking within the annular groove 1c.
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