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.

A reciprocating die roll forming machine for forming a pattern such as a thread form on the outer surface of a cylindrical blank includes at least one set of reciprocating dies operating upon the blank which rotates in place. The machine includes a slide and bearing combination to support the dies belt driven by a servo-motor controlled by a central processing unit. Mechanism is provided to deliver and position a blank for engagement by the dies. In one form, the machine includes multiple die sets to produce multiple parts during one die reciprocation cycle. In another form, the machine employs separate drive mechanisms to independently drive each die of a set.

A reciprocating die roll forming machine for forming a pattern such as a thread form on the outer surface of a cylindrical blank includes at least one set of reciprocating dies operating upon the blank which rotates in place. The machine includes a slide and bearing combination to support the dies belt driven by a servo-motor controlled by a central processing unit. Mechanism is provided to deliver and position a blank for engagement by the dies. In one form, the machine includes multiple die sets to produce multiple parts during one die reciprocation cycle. In another form, the machine employs separate drive mechanisms to independently drive each die of a set.

A crack-proof screw includes a thread formed around a shank. A helical notch continuously and helically extends along the shank and is indented into the shank and the thread. The helical notch is proximal to but spaced apart from a tip of the shank. The notch is trapezoidal in cross section, and has a notch bottom, an open end opening at an outer peripheral surface of the shank oppositely of the notch bottom, and two opposite notch walls extending divergingly from the notch bottom to the open end. The open end is larger in width than the notch bottom. A method of making the screw is also disclosed.

A crack-proof screw includes a thread formed around a shank. A helical notch continuously and helically extends along the shank and is indented into the shank and the thread. The helical notch is proximal to but spaced apart from a tip of the shank. The notch is trapezoidal in cross section, and has a notch bottom, an open end opening at an outer peripheral surface of the shank oppositely of the notch bottom, and two opposite notch walls extending divergingly from the notch bottom to the open end. The open end is larger in width than the notch bottom. A method of making the screw is also disclosed.

[Problem to be Solved] A thread-rolling flat die for a threaded fastener capable of long life and a thread-rolling method using the thread-rolling flat die for a threaded fastener are provided.

[Means for Solving the Problem] A thread-rolling flat die 1 is provided with a first partial bite surface 15 having an inclination with an angle with respect to a finishing surface 13, and a second partial bite surface 16 formed between the first partial bite surface 15 and the finishing surface 13 and having an inclination with an angle with respect to the finishing surface 13. A crest angle 1 of a processing tooth 31 at a thread-rolling starting point 17 in the first partial bite surface 15 is larger than a crest angle 2 of a processing tooth 31 in the finishing surface 13. Therefore, loads applied to dies 10, 50 can be reduced, and this allows a longer life of the thread-rolling flat die 1.

[Problem to be Solved] A thread-rolling flat die for a threaded fastener capable of long life and a thread-rolling method using the thread-rolling flat die for a threaded fastener are provided.

[Means for Solving the Problem] A thread-rolling flat die 1 is provided with a first partial bite surface 15 having an inclination with an angle with respect to a finishing surface 13, and a second partial bite surface 16 formed between the first partial bite surface 15 and the finishing surface 13 and having an inclination with an angle with respect to the finishing surface 13. A crest angle 1 of a processing tooth 31 at a thread-rolling starting point 17 in the first partial bite surface 15 is larger than a crest angle 2 of a processing tooth 31 in the finishing surface 13. Therefore, loads applied to dies 10, 50 can be reduced, and this allows a longer life of the thread-rolling flat die 1.

An electric discharge machining electrode is shaped to form a die for roll forming a dual threaded screw. The electrode is oriented with a face thereof adjacent to a forming surface of the die and placed within an electric discharge machine to cause electric discharge via the electrode to the forming surface of the die, to shape the die to have the geometry required for roll forming of the dual threaded screw. The EDM electrode face has a plurality of troughs and tips substantially matching coarse threads of the screw. Grooves are formed in the tips. The grooves are angled relative the tips and have a geometry substantially matching the fine threads of the screw. The face of the electrode has a form which shapes the forming surface of the die so that the die can roll form the dual threaded screw.

A thread-rolling apparatus includes a base, a feeding unit, a thread-forming assembly, and a distance-sensing assembly. The base mainly includes a movable portion, a first body, and a second body between the movable portion and the first body. The thread-forming assembly includes cooperating first and second dies and a working passage formed between the dies. The distance-sensing assembly includes at least one sensing unit disposed on the first body and a processing module connected to the sensing unit. The cooperation between the sensing unit and the processing module senses changes in a first distance between the first body and the second body in a non-contact manner whereby abnormal variations can be quickly observed and properly coped, and a second distance of the working passage can be in a normal state. Accordingly, the yield rate of the thread-rolling apparatus can be efficiently increased.

The invention relates to methods of stabilizing bone implants, comprising inserting a self-tapping implant having at least two helical grooves running in opposite directions around the implant.