TWI894955B - Nut loosening prevention structure - Google Patents

Abstract

A nut loosening prevention structure and fixing component thereof are used to solve the problem of self-loosening of a nut during screwing. The nut loosening prevention structure includes: a screw, at least one end of which forms an open end, the screw having a threaded portion with a first thread rotating in a first direction and a second thread rotating in a second direction; a first nut having an internal thread rotating in the first direction on the threaded portion of the screw; a second nut having an internal thread rotating in the second direction on the threaded portion of the screw; and a fixing component fitted on the outer wall of both the first nut and the second nut by an inner wall, preventing the first nut and the second nut from rotating independently relative to the screw. The present invention limit the first nut and the second nut from loosening by means of the fixing component.

Description

Nut anti-loosening structure

The present invention relates to a nut anti-loosening structure, and more particularly to a structure for preventing a nut from self-loosening and its fixing member.

Nuts are used for fastening and are widely used in various applications, including machinery, equipment, vehicles, ships, railways, bridges, and buildings. A conventional nut is threaded onto a screw or bolt. The thread can be left-handed or right-handed, and can be used to secure the object being fastened, either as a single nut or as a double nut. Under static conditions, nuts achieve their purpose of fastening. That is, under static loads, the nut will not loosen or fall out. However, under variable loads such as impact and vibration, the nut may loosen or fall out.

Please refer to Figure 1, which is a patent application of China Publication No. CN 102312899 A, which discloses a "fastening device with bidirectional thread". It includes a screw 9 with a thread on one end. The screw 9 is provided with a clockwise thread segment 9a and a counterclockwise thread segment 9b. The counterclockwise thread segment 9b has a smaller diameter than the clockwise thread segment 9a. Two nuts 91 and 92 have corresponding clockwise and counterclockwise internal threads, respectively, so that the two nuts 91 and 92 can be screwed into the clockwise thread segment 9a and the counterclockwise thread segment 9b, respectively. The forward nut 91, which has a clockwise internal thread, has a groove 93 on its end surface. The reverse nut 92, which has a counterclockwise internal thread, has a bump 94 on its end surface that matches the size of the groove 93. The groove 93 and the bump 94 engage and lock together to prevent the two nuts 91 and 92 from loosening.

Because the two nuts 91 and 92 are screwed into the clockwise and counterclockwise threaded segments 9a and 9b of the screw rod 9, respectively, the protrusion 94 is unable to enter the groove 93 when the counterclockwise nut 92 is rotated. This means that the structure disclosed in the patent is unable to prevent the two nuts 91 and 92 from loosening due to vibration during use.

Please refer to Figure 2, which illustrates a "loose-proof fastener" patent disclosed in China Publication No. CN 108386436 A. The fastener comprises a bolt 8, a first nut 81, and a second nut 82. The bolt 8 comprises a right-hand threaded rod 8a and a left-hand threaded rod 8b. The first nut 81 mates with the right-hand threaded rod 8a, while the second nut 82 mates with the left-hand threaded rod 8b. A docking slot 83 is provided on the side of the second nut 82 proximate to the right-hand threaded rod 8a. A protrusion 84 is provided on the side of the first nut 81 proximate to the left-hand threaded rod 8b, and the protrusion 84 mates with the docking slot 83.

When in use, use a tool to install the first nut 81 with the right-hand threaded rod 8a of the lower half of the bolt 8, so that the first nut 81 is kept in the middle part of the bolt 8, and then continue to use a tool to install the second nut 82 with the left-hand threaded rod 8b of the upper half of the bolt 8, and screw the second nut 82 toward the lower half of the bolt 8 to fix the first nut 81, so that the protrusion 84 is slowly screwed into the inside of the docking groove 83 under the forced extrusion pressure, so that the first nut The first nut 81 and the second nut 82 are tightly connected. Once the fastener is engaged, due to the different thread directions of the upper and lower threads of the bolt 8, any loosening of either nut 81 or 82 will only cause the other nut to rotate increasingly tighter. Furthermore, since the first and second nuts 81, 82 are frictionally bonded, forming a near-integrated whole, their positions are permanently fixed, preventing them from loosening under varying loads.

Because the anti-loosening fastener requires the protrusion 84 on the first nut 81 and the engaging groove 83 on the second nut 82, the choice of the first nut 81 and the second nut 82 is limited by the manufacturer, and the manufacturing cost of the first nut 81 and the second nut 82 is relatively high. In particular, the first nut 81 and the second nut 82 may loosen due to vibration during use. Due to the different spiral directions of the right-hand threaded rod 8a and the left-hand threaded rod 8b, the first nut 81 and the second nut 82 may rotate in different spiral directions. This prevents the first nut 81 and the second nut 82 from rotating in opposite directions when one nut loosens due to movement, thereby causing the other nut to rotate increasingly tighter. Instead, the first nut 81 and the second nut 82 may rotate in opposite directions away from the ground. Therefore, the structure disclosed in the patent cannot effectively prevent the first nut 81 and the second nut 82 from loosening due to vibration during use.

In view of this, the conventional nut anti-loosening structure does need to be improved.

To address the aforementioned issues, the present invention aims to provide a nut anti-loosening structure that can be used to tighten the object being fastened, ensuring that the nut will not loosen due to vibration during use.

A second object of the present invention is to provide a nut anti-loosening structure that can be applied to existing nuts, thereby avoiding restrictions on manufacturers and reducing overall costs.

Another object of the present invention is to provide a fixing member that can be used to restrict the two nuts from rotating independently relative to the screw rod, thereby ensuring that the nuts will not become loose due to vibration during use.

Throughout this disclosure, directional terms or similar terms, such as "front," "rear," "left," "right," "upper (top)," "lower (bottom)," "inner," "outer," and "side," are primarily used with reference to the accompanying drawings. These directional terms or similar terms are intended solely to facilitate description and understanding of the various embodiments of the present invention and are not intended to limit the present invention.

The use of the quantifiers "a" or "an" in describing elements and components throughout this invention is for convenience only and to provide a general understanding of the scope of the invention. They should be interpreted as including one or at least one, and the singular also includes the plural, unless it is obvious that it means otherwise.

The nut anti-loosening structure of the present invention comprises: a screw having a first end and a second end, at least one end of the screw forming an open end, the screw having a threaded portion, the threaded portion including a first thread screwed in a first direction and a second thread screwed in a second direction; a first nut having an internal thread and an outer wall, the internal thread being screwed in the threaded portion of the screw in the first direction; a second nut having an internal thread and an outer wall, the internal thread being screwed in the threaded portion of the screw in the second direction, the first nut and the second nut being screwed in the threaded portion of the screw in the second direction. The outer wall has a cross-sectional shape of the same polygon and dimensions; and a fixing member, having an inner wall that fits over the outer walls of the first and second nuts, prevents the first and second nuts from rotating independently relative to the screw. The fixing member is a hollow cylindrical body, the inner wall of which has a plurality of slots, each of which opens at the bottom edge of the inner wall. The number of slots is a positive integer multiple of the number of sides of the outer walls of the first and second nuts. The polygonal corners of the first and second nuts are respectively engaged with the corresponding slots.

The nut anti-loosening structure of the present invention comprises: a screw having a small diameter portion and a large diameter portion adjacent to each other, the small diameter portion having a first thread portion, the large diameter portion having a second thread portion, the first thread portion and the second thread portion being screwed in opposite directions; a first nut having an internal thread and an outer wall, the internal thread being screwed into the first thread portion of the screw in a first direction; a second nut having an internal thread and an outer wall, the internal thread being screwed into the second thread portion of the screw in a second direction, the internal thread of the second nut having a larger diameter than the outer diameter of the first thread portion, one end of the small diameter portion forming an open first end, and the other end of the small diameter portion being aligned with one end of the large diameter portion. Adjacent to the other end of the large diameter portion is the second end of the screw, which has a cap head. The outer walls of the first and second nuts have the same polygonal cross-sectional shape and dimensions. A fixing member is provided, with an inner wall that fits over the outer walls of the first and second nuts, preventing the first and second nuts from rotating independently relative to the screw. The fixing member is a hollow cylindrical body with a plurality of slots on the inner wall. Each slot has an opening formed at the bottom edge of the inner wall. The number of slots is a positive integer multiple of the number of sides of the outer walls of the first and second nuts. The polygonal corners of the first and second nuts are respectively engaged with the corresponding slots.

The fixing member of the present invention is a cylindrical body made of plastic or metal. The cylindrical body has an inner wall whose cross-section is a regular polygon.

Accordingly, the nut anti-loosening structure and its fixing member of the present invention can achieve a primary anti-loosening effect by having the fixing member wrap around the first and second nuts, preventing the first and second nuts from rotating independently relative to the screw. Furthermore, by having a first engaging portion on the first end surface of the screw and a second engaging portion on the inner surface of the top of the fixing member, the second engaging portion can engage with the first engaging portion, thereby achieving a secondary anti-loosening effect by preventing the first and second nuts from rotating synchronously relative to the screw.

The first end of the screw is an open end, the threaded portion is connected to the open end, and the second end of the screw has a cap. Thus, the screw can be selected from various commercially available bolts.

The second nut is closer to the head than the first nut. This creates a gap between the second nut and the head, allowing the flange of the fastener to protrude into the gap, preventing the fastener from falling out.

The fixing member of the present invention is a hollow cylindrical body, the inner wall of which has a plurality of openings, each of which has an opening formed at the bottom edge of the inner wall.

The first end surface of the screw may further include a first engaging portion. The fixing member may include a closed top portion, and the inner surface of the top portion may include a second engaging portion that engages with the first engaging portion. The engagement of the second engaging portion with the first engaging portion further prevents the fixing member, the first nut, and the second nut from rotating relative to the screw.

The fixing member is a shrink film made of PE, PVC, POF, OPS, or PET, and is wrapped around the outer walls of the first and second nuts. This makes the fixing member convenient to use and easily secure to the outer walls of the first and second nuts, while also reducing costs.

One end of the fixing member has a flange protruding from the inner wall toward the center of the fixing member. The flange protrudes into a gap between the second nut and the cap head. This prevents the fixing member from falling out.

The first end surface of the screw may further include a first engaging portion. The fixing member may include a closed top portion, and a second engaging portion may be formed on the inner surface of the top portion. The second engaging portion engages with the first engaging portion. Thus, the engagement of the second engaging portion with the first engaging portion provides a secondary anti-loosening function, preventing the first and second nuts from rotating synchronously relative to the screw.

[The present invention]

1: Screw

1a: First end

1b: Second end

1c: Trail section

1d: Main Path

11: Threaded section

11a: First threaded portion

11b: Second thread portion

12: Hat Head

13: First fitting part

2: First Nut

21: Internal thread

22:Outer wall

3: Second nut

31: Internal thread

32:Outer wall

4: Fixing parts

41: Inner wall

42: flange

43: Top

44:Second chimeric part

5: Fasteners

51: Inner wall

52: Opening slot

53: Top

54:Second chimeric part

55: flange

F: Fixtures

G: Gap area

[Practice]

8: Bolts

8a: Right-hand threaded rod

8b: Left-hand threaded rod

81: First nut

82: Second nut

83: Docking card slot

84: Bump

9: Screw

9a: Clockwise thread segment

9b: Counterclockwise thread segment

93: Groove

94: Bump

[Figure 1] Front view of a fastening device assembly with a bidirectional thread.

Figure 2: Cross-sectional view of the anti-loosening fastener assembly.

[Figure 3] Exploded perspective view of the first embodiment of the present invention.

[Figure 4] A cross-sectional view of the nut of the first embodiment of the present invention when not screwed in.

[Figure 5] A cross-sectional view of the first embodiment of the present invention in use.

[Figure 6] Exploded perspective view of the second embodiment of the present invention.

[Figure 7] A cross-sectional view of the second embodiment of the present invention in use.

[Figure 8] Exploded perspective view of the third embodiment of the present invention.

[Figure 9] A cross-sectional view of the third embodiment of the present invention in use.

[Figure 10] Sectional view along line A-A in Figure 9.

To make the above and other purposes, features, and advantages of the present invention more clearly understood, the following provides a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings.

The directions or similar terms used in this invention, such as "front," "rear," "left," "right," "upper," "lower," "inner," "outer," and "side," are primarily used with reference to the directions in the accompanying drawings. These directions or similar terms are intended solely to facilitate the description and understanding of the various embodiments of the invention and are not intended to limit the invention.

Please refer to Figures 1 and 2, which illustrate a first embodiment of the nut anti-loosening structure of the present invention. The structure may include a screw 1, a first nut 2, a second nut 3, and a fixing member 4. The first nut 2 and the second nut 3 may be threadedly engaged with the screw 1. The fixing member 4 may be used to restrict the first nut 2 and the second nut 3 to rotate in the same direction and not in opposite directions.

The screw 1 can be a conventional threaded rod or bolt, and the present invention is not limited thereto. The screw 1 has a first end 1a and a second end 1b. At least one end of the screw 1 forms an open end. The screw 1 has a threaded portion 11, which is connected to the at least one open end. In this embodiment, the screw 1 is described as a bolt. The first end 1a of the screw 1 forms an open end, the threaded portion 11 is connected to the first end 1a, and the second end 1b of the screw 1 can be a non-open end with a cap 12, or the second end 1b of the screw 1 can be fixed to a predetermined position. The threaded portion 11 includes a first thread that screws in a first direction and a second thread that screws in a second direction. The directions of the first and second threads are opposite, i.e., the first and second threads may be one thread that screws in a clockwise direction and one thread that screws in a counterclockwise direction.

The first nut 2 has an internal thread 21 and an outer wall 22. The first nut 2 can be screwed into the threaded portion 11 of the screw 1 via the internal thread 21. The screwing direction can be in the first direction or the second direction, which is not limited by the present invention. The outer wall 22 is located on the outer surface of the first nut 2 and can have a cross-sectional shape such as a quadrilateral, hexagonal, or polygonal shape, allowing the first nut 2 to be rotated by a tool.

The second nut 3 also has an internal thread 31 and an outer wall 32. The internal thread 31 can be screwed into the threaded portion 11 of the screw rod 1 in a direction opposite to that of the first nut 2. The outer wall 32 is located on the outer surface of the second nut 3 and can have a cross-sectional shape such as a square or hexagonal polygon, allowing the second nut 3 to be rotated by a tool. The cross-sectional shape and dimensions of the outer wall 32 of the second nut 3 can be the same as or different from those of the outer wall 22 of the first nut 2. Preferably, the second nut 3 is adjacent to the head 12, and the cross-sectional shape and size of the outer wall 32 of the second nut 3 are the same as the cross-sectional shape and size of the outer wall 22 of the first nut 2.

The fixing member 4 is a cylindrical body having an inner wall 41. The cross-sectional shape and dimensions of the inner wall 41 match those of the outer walls 22 and 32 of the first and second nuts 2 and 3. Specifically, the fixing member 4 can be fitted with the inner wall 41 over the outer walls 22 and 32 of the first and second nuts 2 and 3, forming a single unit with the first and second nuts 2 and 3. This prevents the first and second nuts 2 and 3 from rotating independently relative to the fixing member 4. The fixing member 4 can be made of a rigid material such as plastic or metal, or a shrink film made of PE, PVC, POF, OPS, or PET, which can be wrapped around the outer walls 22 and 32 of the first and second nuts 2 and 3 to form the fixing member 4.

Preferably, one end of the fixing member 4 has a flange 42 protruding from the inner wall 41 toward the center of the fixing member 4. When the first nut 2 and the second nut 3 are securely screwed into the threaded portion 11 of the screw 1, a gap G is defined between the second nut 3 and the head 12 (as shown in FIG. 4 ). This gap G can be formed by a chamfer of the second nut 3. The fixing member 4 can be fitted onto the outer walls 22, 32 of the first and second nuts 2, 32, from the first end 1a of the screw 1 toward the second end 1b, with the flange 42 protruding into this gap G. This prevents the fixing member 4 from being dislodged from the outer walls 22, 32 of the first and second nuts 2, 32.

Please refer to Figures 4 and 5, which show the use of the first embodiment of the nut anti-loose structure of the present invention. The second end 1b of the screw 1 can be positioned on a fixed object F, and the first end 1a of the screw 1 can protrude from a surface of the fixed object F. The first nut 2 and the second nut 3 can be screwed into the threaded portion 11 of the screw 1. The fixing member 4 can be matched to the outer walls 22 and 32, and the flange 42 of the fixing member 4 protrudes from the gap portion G. In this way, the fixing member 4 can reliably position the first nut 2 and the second nut 3 on the threaded portion 11 of the screw rod 1. Therefore, when the fixture F vibrates, causing the first nut 2 and the second nut 3 to loosen, the first nut 2 and the second nut 3 are matingly secured against the outer walls 22 and 32 by the fixing member 4. Not only can the first nut 2 and the second nut 3 not rotate independently relative to the screw rod 1, but because the first nut 2 and the second nut 3 thread in opposite directions, they form a restraining effect, preventing the first nut 2, the second nut 3, and the fixing member 4 from rotating synchronously in a single direction relative to the screw rod 1. This prevents the first nut 2 and the second nut 3 from loosening.

Please refer to Figures 6 and 7, which are the second embodiment of the nut anti-loosening structure of the present invention. In this embodiment, the screw 1 has a small diameter portion 1c and a large diameter portion 1d with two different outer diameters. One end of the small diameter portion 1c forms the open first end 1a, and the other end of the small diameter portion 1c is adjacent to one end of the large diameter portion 1d. The other end of the large diameter portion 1d forms the second end 1b of the screw 1; the small diameter portion 1c has a first threaded portion 11a, and the large diameter portion 1d has a second threaded portion 11b. The screwing direction of the first threaded portion 11a and the second threaded portion 11b is Conversely, the first threaded portion 11a is threaded onto the first nut 2, and the second threaded portion 11b is threaded onto the second nut 3. The internal thread 21 of the second threaded portion 11b preferably has a larger diameter than the outer diameter of the first threaded portion 11a, allowing the internal thread 31 of the second nut 3 to pass from the first end 1a of the screw 1 through the first threaded portion 11a and into the second threaded portion 11b. In this way, the second end 1b of the screw 1 can be formed into a non-open end with a cap 12, or the second end 1b of the screw 1 can be fixed to a predetermined position.

The first nut 2 and the second nut 3 each have an internal thread 21, 31 and an outer wall 22, 32. The internal threads 21, 31 of the first nut 2 and the second nut 3 thread in different directions. The internal thread 21 of the first nut 2 can be screwed into the first threaded portion 11a of the screw rod 1, and the internal thread 31 of the second nut 3 can be screwed into the second threaded portion 11b of the screw rod 1. The cross-sectional shape of the outer walls 22, 32 of the first nut 2 and the second nut 3 can be a polygonal shape, such as a square or hexagon, so that the first nut 2 and the second nut 3 can be rotated by a tool.

The cross-sectional shapes and dimensions of the outer walls 22 and 32 of the first and second nuts 2 and 3 can be the same or different. Preferably, the cross-sectional shapes and dimensions of the outer walls 22 and 32 of the first and second nuts 2 and 3 are the same. In this way, the inner wall 41 of the fixing member 4 only needs to have a matching single cross-sectional shape and dimensions, and the fixing member 4 can be inserted through the inner wall 41 onto the outer walls 22 and 32 of the first and second nuts 2 and 3. In this way, the first and second nuts 2 and 3 cannot rotate independently relative to the screw 1. In addition, because the first and second nuts 2 and 3 are screwed in opposite directions, they form a restraining effect, preventing the first and second nuts 2 and 3 and the fixing member 4 from rotating synchronously relative to the screw 1.

Furthermore, if the cross-sectional shapes and dimensions of the outer walls 22, 32 of the first and second nuts 2, 3 differ, the cross-sectional shape and dimensions of the inner wall 41 of the fixing member 4 need only be modified to correspond to the corresponding cross-sectional shape and dimensions when the first and second nuts 2, 3 are tightened. This allows the inner wall 41 of the fixing member 4 to fit snugly over the outer walls 22, 32, thereby restricting the first and second nuts 2, 3 from rotating independently relative to the screw 1. This is readily understood by those skilled in the art and will not be elaborated upon.

Continuing with reference to Figures 6 and 7 , the screw 1 described in the aforementioned embodiments may further include a first engaging portion 13 on the end surface of the first end 1a of the screw 1. The fixing member 4 may include a closed top portion 43, and a second engaging portion 44 may be formed on the inner surface of the top portion 43. The second engaging portion 44 may be engaged with the first engaging portion 13, thereby preventing the fixing member 4 from rotating relative to the screw 1. Thus, when the fixing member 4 is mounted on the outer walls 22 and 32 of the first and second nuts 2 and 3, the fixing member 4 not only restricts the first and second nuts 2 and 3 from independently rotating relative to the screw 1, but also further prevents the fixing member 4, the first and second nuts 2 and 3 from rotating relative to the screw 1 by the second engaging portion 44 engaging with the first engaging portion 13. The first and second engaging portions 13 and 44 may be configured as matching straight grooves, cross grooves, grooves, teeth, bumps, ridges, or other structures, and the present invention is not limited thereto.

Please refer to Figures 8, 9 and 10, which are another embodiment of the nut anti-loosening structure of the present invention. The screw 1 can be constructed as described in the above embodiments. In this embodiment, the internal threads 21 and 31 of the first nut 2 and the second nut 3 have different screwing directions. The outer walls 22 and 32 of the first nut 2 and the second nut 3 have the same polygonal shape and size. The fixing member 5 is a hollow circular cylinder. The inner wall 51 of the circular cylinder has a number of open grooves 52. The opening of each open groove 52 is formed at the bottom edge of the inner wall 51. The number of the open grooves 52 is a positive integer multiple of the number of sides of the outer walls 22 and 32 of the first nut 2 and the second nut 3. Thus, when the first nut 2 and the second nut 3 are securely screwed onto the threaded portion 11 of the screw 1, and the polygonal shapes of the outer walls 22 and 32 of the first and second nuts 2 and 3 are aligned, the fixing member 5 can be inserted around the circumferences of the first and second nuts 2 and 3. At this point, the polygonal corners of the first and second nuts 2 and 3 can be respectively engaged with the corresponding openings 52, thereby preventing the fixing member 5 from independently rotating relative to the screw 1. Furthermore, the bottom end of the fixing member 5 may have a flange 55 protruding from the inner wall 51 toward the center of the fixing member 5. The flange 55 can extend into the gap G between the second nut 3 and the head 12.

Preferably, the fixing member 5 has a closed top portion 53, the end surface of the first end 1a of the screw 1 has the first engaging portion 13, and the inner surface of the top portion 53 of the fixing member 5 has a second engaging portion 54, and the second engaging portion 54 can be engaged with the first engaging portion 13, so that the fixing member 5 cannot rotate relative to the screw 1. In this embodiment, the first engaging portion 13 is a polygonal column, and the second engaging portion 54 is a matching polygonal frame. Thus, when the fixing member 5 is fitted around the first nut 2 and the second nut 3, the polygonal corners of the first nut 2 and the second nut 3 not only engage with the corresponding openings 52, thereby preventing the first nut 2 and the second nut 3 from rotating independently relative to the screw 1, but also, by engaging the second engaging portion 54 with the first engaging portion 13, further preventing the first nut 2 and the second nut 3 from rotating relative to the screw 1.

In summary, the nut anti-loosening structure of the present invention utilizes a fixing member that fits around the first and second nuts, thereby preventing the first and second nuts from rotating independently relative to the screw. Furthermore, the first end surface of the screw comprises a first engaging portion, and the top inner surface of the fixing member comprises a second engaging portion that engages with the first engaging portion, thereby achieving a second anti-loosening effect that prevents the first and second nuts from rotating synchronously relative to the screw.

Although the present invention has been disclosed using the preferred embodiments described above, they are not intended to limit the present invention. Any person skilled in the art may make various changes and modifications to the above embodiments without departing from the spirit and scope of the present invention. These changes and modifications are still within the technical scope protected by the present invention. Therefore, the scope of protection of the present invention shall include all changes within the meaning and equivalent scope of the appended patent applications.

1: Screw

1a: First end

1b: Second end

11: Threaded section

12: Hat Head

2: First Nut

21: Internal thread

22:Outer wall

3: Second nut

31: Internal thread

32:Outer wall

4: Fixing parts

41: Inner wall

42: flange

F: Fixtures

Claims (8)

A nut anti-loosening structure includes: a screw having a first end and a second end, at least one end of the screw forming an open end, the screw having a threaded portion, the threaded portion including a first thread screwed in a first direction and a second thread screwed in a second direction; a first nut having an internal thread and an outer wall, the internal thread being screwed in the threaded portion of the screw in the first direction; a second nut having an internal thread and an outer wall, the internal thread being screwed in the threaded portion of the screw in the second direction, the first nut and the second nut having an internal thread and an outer wall. The cross-sectional shape of the outer wall is the same polygon and size; and a fixing piece, which is sleeved on the outer wall of the first nut and the second nut by an inner wall, so that the first nut and the second nut cannot rotate independently relative to the screw, and the fixing piece is a hollow circular cylinder, the inner wall of the circular cylinder has a number of open grooves, the opening of each open groove is formed at the bottom edge of the inner wall, and the number of the open grooves is a positive integer multiple of the number of sides of the outer wall of the first nut and the second nut, and the polygonal corners of the first nut and the second nut are respectively stuck in the corresponding open grooves. As in the nut anti-loosening structure of claim 1, wherein the first end of the screw is formed as an open end, the threaded portion is connected to the open end, and the second end of the screw has a cap head. As in the nut anti-loosening structure of claim 2, wherein the second nut is closer to the cap head than the first nut. A nut anti-loosening structure includes: a screw having a small diameter portion and a large diameter portion adjacent to each other, the small diameter portion having a first thread portion, the large diameter portion having a second thread portion, the first thread portion and the second thread portion being screwed in opposite directions; a first nut having an internal thread and an outer wall, the internal thread being screwed into the first thread portion of the screw in a first direction; a second nut having an internal thread and an outer wall, the internal thread being screwed into the second thread portion of the screw in a second direction, the internal thread of the second nut having a larger diameter than the outer diameter of the first thread portion, one end of the small diameter portion forming an open first end, and the other end of the small diameter portion being aligned with one end of the large diameter portion. Adjacent, the other end of the large diameter portion forms the second end of the screw, and the second end has a cap head. The cross-sectional shape of the outer wall of the first nut and the second nut is the same polygon and size; and a fixing piece, which is sleeved on the outer wall of the first nut and the second nut by an inner wall, so that the first nut and the second nut cannot rotate independently relative to the screw, and the fixing piece is a hollow circular cylinder, and the inner wall of the circular cylinder has a number of open grooves, and the opening of each open groove is formed at the bottom edge of the inner wall. The number of the open grooves is a positive integer multiple of the number of sides of the outer wall of the first nut and the second nut, and the polygonal corners of the first nut and the second nut are respectively stuck in the corresponding open grooves. As in the nut anti-loosening structure of claim 1 or 4, the first end surface of the screw has a first engaging portion, the fixing member has a closed top portion, the inner surface of the top portion has a second engaging portion, and the second engaging portion is engaged with the first engaging portion. In the nut anti-loosening structure of claim 1 or 4, the fixing member is a shrinkage film made of PE, PVC, POF, OPS, or PET, and the shrinkage film is coated on the outer walls of the first nut and the second nut. As in the nut anti-loosening structure of claim 3 or 4, one end of the fixing member has a flange protruding from the inner wall toward the center of the fixing member, and there is a gap between the second nut and the cap head, and the flange protrudes from the gap. As in the nut anti-loosening structure of claim 7, the first end face of the screw rod may also have a first engaging portion, the fixing member has a closed top portion, the inner surface of the top portion has a second engaging portion, and the second engaging portion is engaged with the first engaging portion.