| 摘要 |
An improved fastener assembly includes helical internal and external thread convolutions. A generally helical insert having a plurality of turns is disposed between the internal and external thread convolutions. This insert is resiliently twisted or flexed from a first condition to a fully deflected condition under the influence of torsion forces applied to the insert by the internal and external thread convolutions. In one embodiment of the invention, the insert has four side surfaces. When this insert is in the first condition, one pair of side surfaces is disposed in abutting engagement with the leading flanks of the internal and external thread convolutions. At this time the other side surfaces of the insert are spaced apart from the trailing flank surfaces of the thread convolutions. As used herein, the leading flank surfaces of the thread convolutions are the flank surfaces which, when the thread is about to be assembled with a mating thread, face the mating thread. Upon twisting of the insert to a deflected condition, the side surfaces of the insert move away from the leading flanks of the thread convolutions and move into abutting engagement with the trailing flanks of the thread convolutions. Under conditions in which it is desired to pretension the internal thread convolution, the internal thread convolution is formed with a smaller pitch than the external thread convolution. In another embodiment of the invention, the insert is provided with an arcuate surface which engages one of the thread convolutions and a pair of side surfaces to engage the flanks of the other thread convolution. The internal and external thread convolutions may have different pitches to provide a locking action between the insert and the thread convolutions.
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