| 摘要 |
Double nail hard to be loosened is composed of main nail(1) and subsidiary ones(4).The main nail has grooves(7) along which the subsidiary nails can be inserted. After driving the nail, the nail can be fixed tightly by hammering the subsidiary ones more, the subsidiary ones being bent and thrusted in the wood. Ordinary nail can be used as a subsidiary one when the grooves are made rectangulars in their cross section.
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