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: A fastener assembly is provided and includes a fastener member and a washer member. The fastener member includes an end, an opposing head, and an elongated threaded body portion extending therebetween. The threaded body defines a center axis. The head includes a pawl arm having a pawl tooth and a flange. The washer member includes an axial aperture formed therethrough and a lock tab extending therefrom. The lock tab is configured to be received within a recess defined in a substrate member to rotationally fix the washer member relative to the substrate member. The washer member further includes a plurality of lock teeth. The pawl tooth is configured to intermesh with the lock teeth to allow rotation of the fastener member relative to the washer member in a first direction about the center axis, and substantially prevent rotation in an opposite second direction about the center axis.