Abstract: Fastening art with double nuts for a dual-threaded screw structure is provided, in which loosening is not created even if the structure is subjected to vibration. A spring washer is caused to intervene between the nuts, when double nuts of an inner nut and an outer nut are screwed onto a thread portion on which dual-threaded screw is formed. Only by tightening the outer nut, also the inner nut is tightened and the spring washer is compressed. Both axial force for clamping the fastened member and axial force between the nuts can be secured with the spring washer, so that loosening does not occur easily.

Abstract: A dual-threaded screw structure having two kinds of threads formed on a shank, namely, a first thread consisting of one or more threads and a second thread having a lead larger than a lead of the first thread is provided herein. The claimed configuration has a beneficial effect of preventing looseness when the screw structure is fastened with double nuts. One embodiment of the present invention exhibits an example of a dual-threaded screw structure, in which a root diameter between the ridges of the hill-like second thread ridges is formed to be larger by 10% of a height of the ridges than an effective diameter of a first thread. In this case, an inner diameter of an internal thread of a second nut for preventing looseness is formed to be larger than the effective diameter of the first thread by 10% of the height of the ridges.

Abstract: The dual-threaded screw structure 1 has a first thread (S1) and a second thread (S2) with various leads formed on the dual-thread portion and has a function of preventing loosening without insufficiency in strength of the dual-thread portion. This dual-thread portion is composed of a first thread (S1) consisting of a coarse thread with a standard pitch P and a specific second thread (S2). The second thread (S2) is formed continuously on the thread ridge of the first thread (S1). The second thread (S2) has a sectional shape of this thread groove same as or substantially same as the first thread (S1), has a same twisting direction as the first thread (S1) and is a multi-threaded thread having threads with a triangular sectional shape and having a lead (L=n*P) a determined number (n)-times of a standard pitch P.

Abstract: The dual-threaded screw structure 1 has a first thread (S1) and a second thread (S2) with various leads formed on the dual-thread portion and has a function of preventing loosening without insufficiency in strength of the dual-thread portion. This dual-thread portion is composed of a first thread (S1) consisting of a coarse thread with a standard pitch P and a specific second thread (S2). The second thread (S2) is formed continuously on the thread ridge of the first thread (S1). The second thread (S2) has a sectional shape of this thread groove same as or substantially same as the first thread (S1), has a same twisting direction as the first thread (S1) and is a multi-threaded thread having threads with a triangular sectional shape and having a lead (L=n*P) a determined number (n)-times of a standard pitch P.