Screws that are difficult to loosen

Abstract

To provide a screw that overcomes the drawbacks of preventing loosening and loosening of screws, and that is effective in preventing loosening even for small screws. [Solution] A screw that is difficult to loosen is composed of a shank 10 and a head 19, with a threaded portion 11 and a threaded portion 12 formed on the shank 10. The pitch 17 of the threaded portion 11 and the pitch 18 of the threaded portion 12 are equal, and the lead angle of the threaded portion 11 and the lead angle of the threaded portion 12 are also equal, but the helix of the thread 13 of the threaded portion 11 and its extension do not coincide with the helix of the thread 14 of the threaded portion 12 and its extension, as shown by 15c. The male thread of the threaded portion 11 advances while forming a root of the female thread in the fastener, and because the male thread of the threaded portion 12 is misaligned with the male thread of the threaded portion 11, it approaches the flank of the female thread, comes into contact with it, and advances while applying pressure. After fastening, the flank of the male thread applies pressure to the flank of the female thread that it comes into contact with, and the frictional resistance generated by the pressure makes the screw difficult to loosen.

Description

[Technical Field]

[0001] This invention relates to screws that are difficult to loosen. [Background technology]

[0002] Conventional locking screws and screws that prevent loosening are achieved by applying locking agents, forming protrusions to prevent loosening, using flat washers or spring washers, or covering the threads with seals or covers. However, there is room for improvement in the above methods in terms of manufacturing costs, convenience during use, and applications where the screws are repeatedly loosened. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 6-330928 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional locking screws and screws that prevent loosening have problems such as high manufacturing costs, poor convenience, and being unsuitable for applications where fastening screws are repeatedly loosened. [Means for solving the problem]

[0005] To solve the above problem, this invention provides a screw that is difficult to loosen by pinching the threads of a female screw with the threads of a male screw, or by using the threads of a male screw to spread the threads of a female screw toward the tip and head, so that the slope of the threads of the male screw applies pressure to the slope of the threads of the female screw, and the frictional resistance generated by the pressure makes it difficult to loosen, solving the problem.

[0006] The screw that is difficult to loosen according to the present invention as set forth in claims 1 and 2 will be explained using Figures 1 to 8. In the following explanations, the component on which a male thread is formed will be referred to as a screw, and the component on which a female thread is formed will be referred to as a fastener.

[0007] The loosening-resistant screw 1 in Figure 1 is a screw to which claim 1 applies. Screw 1 is composed of a shank 10 and a head 19, with threaded portions 11 and 12 formed on shank 10. In Figure 2, which shows the helix of the screw shaft of screw 1 expanded from a cylinder onto a plane, the lead angle 11a of threaded portion 11 and the lead angle 12a of threaded portion 12 are equal, and as shown in Figure 1, the pitch 17 of threaded portion 11 and the pitch 18 of threaded portion 12 are also equal. However, as shown by dimension line 15c, line 11b indicating the crest of the thread on threaded portion 11 and line 12b indicating the crest of the thread on threaded portion 12 in Figure 2 do not coincide, and line 12b indicating the crest of the thread on threaded portion 12 is shifted toward the tip from line 11b indicating the crest of the thread on threaded portion 11.

[0008] The loosening-resistant screw 2 in Figure 3 is a screw to which claim 1 applies. Screw 2 is composed of shank 20 and head 29, with threaded portion 21 and threaded portion 22 formed on shank 20. In Figure 4, which shows the helix of the screw shaft of screw 2 expanded from a cylinder onto a plane, lead angle 21a of threaded portion 21 and lead angle 22a of threaded portion 22 are equal, and as shown in Figure 3, pitch 27 of threaded portion 21 and pitch 28 of threaded portion 22 are also equal. However, line 21b indicating the crest of the thread of threaded portion 21 in Figure 4 and line 22b indicating the crest of the thread of threaded portion 22 do not coincide, as shown by dimension line 25c, and line 22b indicating the crest of the thread of threaded portion 22 is shifted toward the head from line 21b indicating the crest of the thread of threaded portion 21.

[0009] The loosening-resistant screw 3 in Figure 5 is a screw to which claim 2 applies. Screw 3 is composed of shank 30 and head 39, with shank 30 formed with threaded portion 31, threaded portion 32, and intermediate threaded portion 35. In Figure 6, which shows the helix of the screw shaft of screw 3 expanded from a cylinder onto a plane, lead angle 31a of threaded portion 31 and lead angle 32a of threaded portion 32 are equal, and as shown in Figure 5, pitch 37 of threaded portion 31 and pitch 38 of threaded portion 32 are also equal. However, line 31b indicating the crest of the thread of threaded portion 31 in Figure 6 and line 32b indicating the crest of the thread of threaded portion 32 do not coincide, as shown by dimension line 35c, and line 32b indicating the crest of the thread of threaded portion 32 is shifted toward the tip from line 31b indicating the crest of the thread of threaded portion 31.

[0010] Between the threaded portion 31 on the tip side and the threaded portion 32 on the head side in Figure 6, an intermediate threaded portion 35 is formed to connect the threaded portion 31 on the tip side and the threaded portion 32 on the head side, and the crest line of the thread of the intermediate threaded portion 35 is positioned as shown in 35b, connecting the threads of threaded portion 31 and threaded portion 32 so that the threads of threaded portion 32 can be fastened and unfastened without damaging the female thread of the fastener.

[0011] The loosening-resistant screw 4 in Figure 7 is a screw to which claim 2 applies. Screw 4 is composed of shank 40 and head 49, with shank 40 formed with threaded portion 41, threaded portion 42, and intermediate threaded portion 45. In Figure 8, which shows the helix of the screw shaft of screw 4 expanded from a cylinder onto a plane, lead angle 41a of threaded portion 41 and lead angle 42a of threaded portion 42 are equal, and as shown in Figure 7, pitch 47 of threaded portion 41 and pitch 48 of threaded portion 42 are also equal. However, line 41b indicating the crest of the thread of threaded portion 41 in Figure 8 and line 42b indicating the crest of the thread of threaded portion 42 do not coincide, as shown by dimension line 45c, and the line indicating the crest of the thread of threaded portion 42 is shifted toward the head from the line indicating the crest of the thread of threaded portion 41.

[0012] Between the threaded portion 41 on the tip side and the threaded portion 42 on the head side in Figure 8, an intermediate threaded portion 45 is formed to connect the threaded portion 41 on the tip side and the threaded portion 42 on the head side, and the crest line of the thread of the intermediate threaded portion 45 is positioned as shown in 45b, connecting the threads of threaded portion 41 and the threads of threaded portion 42 so that the threads of threaded portion 42 can be fastened and unfastened without damaging the female thread of the fastener.

[0013] In the case of the screw of this invention, if the threaded portion on the head side is misaligned towards the tip, the male threads of the threaded portion on the tip side and the male threads of the threaded portion on the head side will apply pressure so that they pinch the adjacent female thread in the center, and if the threaded portion on the head side is misaligned towards the head, the male threads of the threaded portion on the tip side and the male threads of the threaded portion on the head side will apply pressure so that they push the adjacent female thread apart towards the tip and head. [Effects of the Invention]

[0014] Conventional locking and loosening prevention functions require costs such as forming protrusions, applying locking agents to screws, and incorporating flat washers or spring washers, but these costs are not necessary with the screws of this invention, which do not require any special components.

[0015] The screw of this invention is a screw in which the threads of the male screw pinch the threads of the female screw of the fastener, or the threads of the male screw push the threads of the female screw of the fastener apart, so that the slope of the male screw thread applies pressure to the slope of the female screw thread, and the frictional resistance generated by the pressure makes it difficult to loosen, and it does not require any protrusions, so it can be easily applied to small screws and miniature screws.

[0016] Previous methods of preventing loosening or preventing loosening have been to dig a protrusion into the fastener or to glue the screw and the female thread of the fastener together. These methods have the potential to damage the female thread of the fastener when it needs to be unscrewed, and if the female thread of the fastener is damaged, re-fastening may result in a loss of the effectiveness of the locking or preventing loosening. The screw of this invention is designed not to damage the female thread of the fastener when it is unscrewed, and will maintain its effectiveness in preventing loosening even after repeated tightening and unscrewing. [Brief explanation of the drawings]

[0017] [Figure 1] This is a diagram of a screw of this invention that does not have an intermediate threaded portion, and the threaded portion on the head side is shifted toward the tip. [Figure 2] This is a diagram of the screw helix in Figure 1 expanded from a cylinder onto a plane. [Figure 3] This is a diagram of a screw of this invention that does not have an intermediate threaded portion, with the threaded portion on the head side shifted toward the head. [Figure 4] This is a diagram of the screw helix in Figure 3 unfolded from a cylinder onto a plane. [Figure 5] This is a diagram of a screw of this invention that has an intermediate threaded section, but the threaded section on the head side is shifted toward the tip. [Figure 6] This is a diagram of the screw helix in Figure 5 expanded from a cylinder onto a plane. [Figure 7]This is a diagram of a screw of this invention that has an intermediate threaded section, but the threaded section on the head side is shifted toward the head. [Figure 8] This is a diagram of the screw helix in Figure 7 unfolded from a cylinder onto a plane. [Figure 9] This is a diagram of a screw without an intermediate threaded portion used to explain the form for implementing the invention. [Figure 10] This is a diagram of the spiral wire of screw 5 in Figure 9 unfolded from a cylinder onto a plane. [Figure 11] This is a diagram of the male thread of the screw shaft of screw 5 in Figure 9 and the female thread of the fastener. [Figure 12] This is a diagram of screw 5 in Figure 9 with threads 61 to 67 screwed in. [Figure 13] This diagram shows the action and reaction of pressure acting on the slope of a screw thread. [Figure 14] This is a diagram of screw 5 in Figure 9, with all male threads tightened and the pressure balanced. [Figure 15] This is an example of settings when rolling a screw to apply pressure so that the male thread pinches the female thread. [Figure 16] This is an example of settings for rolling a screw that applies pressure so that the male thread spreads the slope of the female thread. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following explains the mode for carrying out the invention. The mode for carrying out the invention assumes a tapping type 1 screw that conforms to claim 1.

[0019] Screw 5 in Figure 9 is a screw shank according to claim 1, characterized in that it has a threaded portion on the screwing side and a threaded portion on the opposite side of the screwing side, the pitch of the threaded portion on the screwing side and the pitch of the threaded portion on the opposite side of the screwing side are equal, the lead angle of the threaded portion on the screwing side and the lead angle of the threaded portion on the opposite side of the screwing side are also equal, but the helix of the threads on the screwing side and its extension do not coincide with the helix of the threads on the threaded portion on the opposite side of the screwing side and its extension. Note that the screw 5 used in this explanation has a configuration in which the threaded portion on the head side is offset toward the tip, so that the male threads pinch the female threads, making it difficult to loosen. This explanation will be given in Figure 13, which enlarges the area surrounded by the dotted line 90, showing the engagement of the male thread of screw shaft 50 of screw 5 with the female thread of fastener 70. Also, in all of the diagrams used, the left side shows the tip side of the screw and the right side shows the head side of the screw.

[0020] Figure 10 is a diagram of the helix of the screw shaft of screw 5 expanded from a cylinder onto a plane. Although not shown in Figure 9 to avoid complication, the pitch of thread portion 51 of screw 5 and the pitch of thread portion 52 are equal, and in Figure 10 the lead angle 51a of thread portion 51 and the lead angle 52a of thread portion 52 are also equal, however, line 51b indicating the crest of the thread of thread portion 51 and line 52b indicating the crest of the thread of thread portion 52 do not coincide as shown by dimension line 55c, and line 52b indicating the crest of the thread of thread portion 52 is shifted towards the tip more than line 51b indicating the crest of the thread of thread portion 51.

[0021] The mechanism that makes it difficult to loosen is explained using Figures 11 to 14.

[0022] The first feature of the screw of this invention is the tip-side thread portion 51, depicted in the lower left of Figure 11. Tip-side thread portion 51, formed at the tip end of screw shaft 50, serves to form a female thread in fastener 70. Threads 61 to 62 of tip-side thread portion 51 rise while changing from small threads to a regular thread shape, similar to the threads of a typical self-tapping screw. In screw 5 of this invention, threads 65 to 64 on the unscrewing side of thread portion 51 are also formed to change from small threads to a regular thread shape, and threads 65 to 64 are formed as if the shape of threads 61 to 62 is the inverse of that of threads 61 to 62. This shape allows screw 5 to be fastened and unscrewed without damaging the root of the female thread of fastener 70.

[0023] The second feature of the screw of this device is the head-side thread portion 52, depicted in the lower right of Figure 11. The position of the crest of the thread on the head-side thread portion 52 is offset distally from the center of the thread root of the female thread of the fastener by the width indicated by dimension line 57. In Figure 10, which shows the helix of the screw shank unfolded from a cylinder to a plane, the crest line and its extension of the tip-side thread do not coincide with the crest line and its extension of the head-side thread, as indicated by dimension line 55c. Therefore, the crest line 52b of the thread on the head-side thread portion 52 is offset distally from the crest line 51b of the thread on the tip-side thread portion 51. This is why the crest of thread 67 on the head-side thread portion 52 in Figure 11 is offset distally from the center of the thread root between thread 76 and thread 77 on the fastener 70. This offset applies to all of threads 66, 67, 68, and 69 on the head-side thread portion 52. Furthermore, if the helix of this screw is misaligned, the threaded portion on the head side may collide with the female thread and cause damage when it is screwed in. For this reason, thread 66 changes from the small thread shape to the regular thread shape as it is screwed in, from thread 67. When unscrewing, it is loosened in the reverse order, from thread 69, which has the small thread shape, to thread 68, which has the regular thread shape. This change in thread shape allows screw 5 to be fastened and unscrewed without damaging the root of the female thread of fastener 70.

[0024] Next, the female thread formed in fastener 70 will be explained using Figure 11. The female thread of fastener 70 is formed by the male thread of threaded portion 51 at the tip end of screw shaft 50. The pitch of the roots of the formed female thread all matches the pitch of the male thread of threaded portion 51 at the tip end of screw shaft 50.

[0025] Figure 12 shows the state when thread 61 of thread portion 51 to thread 67 of thread portion 52 are screwed in. Male thread 64 is located in the thread root between female thread 75 and female thread 76, and male thread 67 is located in the thread root between female thread 78 and female thread 79. At this time, the distance on dimension line 54 from the top of thread 64 to the top of thread 67 is shorter than the distance on dimension line 56 from the center of the thread roots of female thread 75 and female thread 76 to the center of the thread roots of female thread 78 and female thread 79, so thread 67 approaches female thread 78, and the slope of the thread on the tip side of thread 67 comes into contact with the slope of the thread on the head side of thread 78, applying pressure.

[0026] Figure 13 shows an enlarged view of the state in which thread 67 is screwed into thread 61 on screw shaft 50 in Figure 12. When screw shaft 50 rotates clockwise in the direction of arrow 81, dimension line 54, which indicates the distance between the center line of the crest of thread 61 on male thread 64 and the center line of the crest of thread 67 on male thread 64, is shorter than dimension line 56, which indicates the distance from the center of the thread roots of female threads 75 and 76 to the center of the thread roots of female threads 78 and 79. When thread 66 on screw shaft 50 is screwed into the thread root between female threads 78 and 79, its small size does not apply pressure to the flank of the female thread. However, when thread 67, which has a regular thread shape, is screwed into the thread root between female threads 78 and 79, the flank of the thread on the tip side of male thread 67 approaches and comes into contact with the flank of the thread on the head side of female thread 78, applying pressure toward the tip on the flank of the thread on the head side of female thread 78. This pressure creates frictional resistance, making the screw difficult to loosen.

[0027] Next, using the same diagram in Figure 13, we will explain the flow of pressure acting on the thread slopes of each thread. Screw shaft 50 rotates clockwise in the direction of arrow 81. As a result, the thread slope at the tip of thread 67 applies pressure (arrow 82) to the thread slope at the head side of female thread 78. This force is transmitted (arrow 83) to the thread slope at the tip side of female thread 76, which is integrated with female thread 78 in fastener 70. The thread slope at the tip side of female thread 76 applies pressure to the thread slope at the head side of adjacent male thread 64. Because male thread 64 is integrated with male thread 67 in screw shaft 50, the pressure of female thread 76 is returned to female thread 76 as a repulsive force (arrow 84). The repulsive force received by female thread 76 is transmitted (arrow 85) to female thread 78, which is integrated with fastener 70, and is transmitted as a repulsive force from the thread slope at the head side of female thread 78 to the thread slope at the tip side of male thread 67. This repetition of pressure and repulsive force compresses the slope of the thread on the tip side of the female thread 76 of the fastener 70, which is softer than the material of the screw shaft, and the slope of the thread on the head side of the female thread 78 of the fastener 70, and when the balance of pressure and repulsive force is achieved between the male thread 67 and the female thread 78, and between the male thread 64 and the female thread 76, the tightening state becomes stable while maintaining the frictional force.

[0028] Figure 14 shows the state when all the threads of the screw part 50 are screwed in, and the pressure and repulsion forces are balanced between the male thread 62 on the tip side and the female thread 72 of the fastener, the male thread 63 on the tip side and the female thread 73 of the fastener, the male thread 64 on the tip side and the female thread 74 of the fastener, the female thread 76 of the fastener and the male thread 67 on the head side, and the female thread 77 of the fastener and the male thread 68 on the head side. The frictional resistance caused by the pressure on the slopes of the threads that come into contact makes it difficult for the fastener to loosen.

[0029] Next, we will explain the flat dies used in thread rolling. We recommend using flat dies to manufacture the screws of this invention. To achieve the goal described in claim 1, it is important that the pitch of the thread at the tip end and the thread at the head end are the same, and that the lead angle of the thread at the tip end and the thread at the head end are the same, but that the helix windings of the thread at the tip end and the thread at the head end are mismatched and the amount of misalignment can be adjusted. For this reason, we recommend creating separate flat dies for the thread at the tip end and the thread at the head end, and using jigs or spacers to adjust their position vertically and horizontally.

[0030] Figure 15 shows an example of a setting for rolling a screw in which the male thread pinches the female thread toward the center and the slope of the male thread applies pressure to the slope of the female thread, making it difficult to loosen.By shifting the flat die 111 that rolls the thread portion on the head side forward, the spiral of the thread on the thread portion on the head side of the rolled screw is shifted toward the tip.

[0031] Figure 16 shows an example of settings for rolling a screw in which the male thread spreads the female thread toward the tip and head, and the male thread's flank applies pressure to the female thread's flank, making it difficult to loosen. By shifting the flat die 211 that rolls the head side of the thread backward, the spiral of the thread on the head side of the rolled screw is shifted toward the head. [Explanation of symbols]

[0032] 1. A screw of this invention that does not have an intermediate threaded portion and the threaded portion on the head side is shifted toward the tip. 2. Screws of this invention that do not have an intermediate threaded portion and the threaded portion on the head side is misaligned toward the head. 3. Screws with an intermediate threaded section, but with the head side threaded section displaced toward the tip. 4. Screws with an intermediate threaded section of this device, but with the head-side threaded section displaced toward the head 5 Screws without intermediate threads used to explain the mode for carrying out the invention 10 Shank of screw 1 11 Threaded portion at the tip of screw 1 11a Lead angle of thread portion 11 on the tip side of screw 1 11b A line that develops the top of the thread of the threaded portion 11 at the tip side of the screw 1 12 Head side thread of screw 1 12a Lead angle of the screw part 12 on the head side of the screw 1 12b A line showing the top of the thread of the screw part 12 on the head side of the screw 1 13 Thread of the threaded portion 11 on the tip side of the screw 1 14 Threads of screw part 12 on the head side of screw 1 15c Misalignment of the helix between the threaded portion 11 on the tip side of the screw 1 and the threaded portion 12 on the head side 17 Pitch of threaded portion 11 at the tip of screw 1 18 Pitch of thread part 12 on the head side of screw 1 19 Head of screw 1 20 Shank of screw 2 21 Threaded portion at the tip of screw 2 21a Lead angle of the threaded portion 21 on the tip side of the screw 2 21b A line that develops the top of the thread of the threaded portion 21 at the tip side of the screw 2 22 Threaded portion on the head side of screw 2 22a Lead angle of the screw part 22 on the head side of the screw 2 22b A line showing the top of the thread of the screw part 22 on the head side of the screw 2 23 Thread of the screw portion 21 on the tip side of the screw 2 24 Thread of screw part 22 on the head side of screw 2 25c Misalignment of the helix between the threaded portion 21 on the tip side of the screw 2 and the threaded portion 22 on the head side 27 Pitch of the threaded portion 21 at the tip of the screw 2 28 Pitch of the threaded portion 22 on the head side of the screw 2 29 Head of screw 2 30 Shank of screw 3 31 The threaded portion 31 at the tip of the screw 3 with the intermediate threaded portion 31a Lead angle of the threaded portion 31 at the tip side of the screw 3 with an intermediate threaded portion 31b A line that develops the top of the thread of the thread portion 31 at the tip side of the screw 3 that has an intermediate thread portion 32 Head side thread portion of screw 3 with intermediate thread portion 32 32a Lead angle of the screw part 32 on the head side of the screw 3 with an intermediate thread part 32b A line showing the top of the thread of the screw portion 32 on the head side of the screw 3 with an intermediate thread portion. 33 Thread of the tip side thread portion 31 of the screw 3 with the intermediate thread portion 34 Threads of the head side thread 32 of the screw 3 with the intermediate thread 35 Middle thread of screw 3 with middle thread 35b A line showing the crest of the middle thread 35 of the screw 3 with the middle thread 35c Misalignment of the helix between the tip side thread 31 and the head side thread 32 of the screw 3 with an intermediate thread 36 Thread of the middle thread 35 of the screw 3 with middle thread 37 Pitch of the threaded portion 31 at the tip of the screw 3 with an intermediate threaded portion 38 Pitch of the threaded portion 32 at the tip of the screw 3 with the intermediate threaded portion 39 Head of screw 3 with intermediate thread 40 Shank of screw 4 41 The threaded portion 41 at the tip of the screw 4 with the intermediate threaded portion 41a Lead angle of the threaded portion 41 at the tip side of the screw 4 with an intermediate threaded portion 41b A line that develops the top of the thread of the thread portion 41 on the tip side of the screw 4 that has an intermediate thread portion 42 Head side thread part of screw 4 with intermediate thread part 42 42a Lead angle of the screw part 42 on the head side of the screw 4 with an intermediate thread part 42b A line showing the top of the thread of the screw portion 42 on the head side of the screw 4 with an intermediate thread portion 43 Thread of the tip side thread portion 41 of the screw 4 with the intermediate thread portion 44 Threads of the head side thread 42 of the screw 4 with the intermediate thread 45 Middle thread of screw 4 with middle thread 45b A line showing the crest of the middle thread 45 of the screw 4 with the middle thread 45c Misalignment of the helix between the tip side thread 41 and the head side thread 42 of the screw 4 with an intermediate thread 46 Thread of the middle thread 45 of the screw 4 with the middle thread 47 Pitch of the threaded portion 41 at the tip of the screw 4 with the intermediate threaded portion 48 Pitch of the threaded portion 42 at the tip of the screw 4 with the intermediate threaded portion 49 Head of screw 4 with intermediate thread 50 Shank of screw 5 51 Threaded portion at the tip of screw 5 51a Lead angle of the threaded portion 51 at the tip side of the screw 5 without an intermediate threaded portion 51b A line that develops the top of the thread of the thread portion 51 at the tip side of the screw 5 that does not have an intermediate thread portion 52 Threaded portion on the head side of screw 5 51a Lead angle of the screw portion 52 on the head side of the screw 5 without an intermediate screw portion 51b A line that develops the top of the thread of the screw portion 52 on the head side of the screw 5 that does not have an intermediate thread portion 53 Threaded portion of fastener 54 Dimension line showing the distance from the center of the crest of thread 64 to the center of the crest of thread 67 55 Dimension line showing the distance from the center of the thread roots of threads 73 and 74 of the fastener to the center of the thread roots of threads 76 and 77 55c Misalignment of the spiral between the threaded portion 51 on the tip side and the threaded portion 52 on the head side of the screw 5 without an intermediate threaded portion 56 Dimension line showing the distance from the center of the thread root of thread 75 and thread 76 of the fastener to the center of the thread root of thread 78 and thread 79 57 Dimension line showing the error between the center of the thread root of the fastener and the crest of the threaded portion 52 on the head side of the screw 5 59 Screw 5 head 61, 62, 63, 64, 65 Each thread of the screw part on the tip side of screw 5 66, 67, 68, 69 Each thread of the screw part on the head side of screw 5 70 Fasteners 71, 72, 73, 74, 75, 76, 77, 78, 79 Threads of fasteners 81 Arrow indicating clockwise rotation of screw 5 82 Pressure exerted by male thread 67 on the flank of thread 76 83 Pressure Arrow 84 Repulsive force generated on the slope of the head side of the male screw thread 64 85 Repulsive Arrow 110 Flat die for rolling the threaded part at the tip 111 Flat die for rolling the screw part on the head side 112 spacer 113 Spacer 114 Blank 115 Screw products in which the male thread slope is sandwiched between the female thread slope 210 Flat die for rolling the threaded part at the tip 211 Flat die for rolling the screw part on the head side 212 Spacer 213 Spacer 214 Blank 215 Screw product in which the male thread flank expands the female thread flank

Claims

1. A screw shaft is formed with a screw portion on the side where it is screwed in and a screw portion on the opposite side of the side where it is screwed in, and the pitch of the screw portion on the side where it is screwed in and the screw portion on the opposite side of the side where it is screwed in are The pitches of the screw portions are equal, and the lead angle of the screw portion on the side where the screw is screwed in is also equal to the lead angle of the screw portion on the opposite side of the side where the screw is screwed in, but the helix of the thread of the screw portion on the side where the screw is screwed in and its extension do not coincide with the helix of the thread of the screw portion on the opposite side of the side where the screw is screwed in and its extension.

2. 2. The screw shaft according to claim 1, further comprising an intermediate threaded portion that connects the threaded portion on the screwing side with the threaded portion on the opposite side to the screwing side.

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