Development of Anti-loosening Screw Fasteners

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The authors propose a new type of helix for anti-loosening screw fastener, the way to manufacture it and the evaluation of its performance. Loosening tests for conventional screws and so-called anti-loosening nuts are first reported and discussed. It is shown that human beings have not yet succeeded in the prevention of loosening of screw fasteners without sacrificing some of their important features. The mechanism of loosening is discussed and the two main factors that cause loosening are outlined. The first is due to the relative slip between the bolt threads and the nut threads, while the second is due to the relative slip between the bearing surface of the nut and the surface of the fastened material. A new screw shape that aims at suppressing the former factor is proposed and a method for producing the appropriate threads on the bolt is discussed. The new shape is named "Step-Lock Bolt." The performance of the bolt with this shape is examined to prove the efficacy of the idea.