JP2010164153A - Looseness preventing bolt and nut - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a looseness preventing bolt and nut which are capable of appropriately preventing looseness due to vibration of an object to be mounted with a simple structure. <P>SOLUTION: The cross section of a head 30a in a direction perpendicular to a rotational axis has a polygonal shape with at least a pair of opposite sides approximately parallel to each other. The center of rotation of the shaft 30b is set at equal distances from both side of any pair of approximately parallel opposite sides and in a position displaced from the center toward any end in the extending direction of the pair of opposite sides. Therefore, the capability of a rotating work by using a normal tool is secured, and the rotation moment of the head in only one direction can be increased. Consequently, a function of preventing looseness due to slight vibration can be enhanced as compared to conventional heads each having a uniform rotation moment. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a loosening prevention bolt and nut, and more particularly to a bolt or nut having an outer edge-shaped head having a substantially polygonal cross section in a direction perpendicular to a rotation axis and having two substantially parallel sides facing each other.

  Bolts and nuts used for fixing various members in a high-voltage power transmission tower or the like are generally fastened and fixed with a single nut. However, for example, in the angle steel tower, when several years have passed since construction, there may be a situation in which the bolts and nuts attached are loosened and dropped due to slight vibration caused by the wind. Therefore, the tower is inspected regularly or temporarily. However, there is a possibility that the bolts and nuts may fall off in the gap of the inspection cycle. Since loosening and dropping off of bolts and nuts causes a lack of design strength of the object to be attached, it is essential to take measures to prevent the bolts and nuts from being tightened.

  Conventionally, cotter bolts and nuts have been used in insulator devices and the like. FIG. 8 shows an example of a cotter bolt and a nut used for connecting the overhead wire fitting. As shown in the figure, a cotter bolt 54 (head 54a, shaft portion 54b) is inserted into the through hole of the combined overhead wire fittings 50, 52, and a nut 56 is attached to the cotter bolt 54. In order to prevent the nut 56 from slipping off, a pin hole 58 is formed in the shaft portion 54b of the bolt 54, the split pin 60 is inserted into the pin hole 58, and the tip 60a thereof is connected to both shaft portions 54b. It is cracked and fixed to the side. Even when the nut 56 is loosened due to the attachment of the split pin 60, the nut 56 is restrained by the split pin 60, and the drop off from the bolt 54 is prevented.

  When the split pin 60 used for such a cotter bolt 54 is not split enough, the tightened state may gradually loosen due to vibration of the bolt 54 and fall off. Further, there is a case where only the bolt 54 is attached and the attachment of the split pin 60 is forgotten. When the split pin 60 is not attached, the nut 56 may loosen and fall off due to slight vibration of the overhead wire fittings 50 and 52 caused by wind or the like.

  In addition, as a conventional measure for preventing loosening of bolts and nuts, Idaring (registered trademark) may be used, but attaching bolts to all bolts and nuts in bolt tightening work in steel towers, etc. This leads to complications and increased costs.

  As a proposal for preventing loosening without using an additional member for the nut, there is a technique of Patent Document 1. This technology uses three stages of upper, middle, and lower nuts, and introduces the concept of eccentricity of screw holes on the upper and lower sides of the interrupted middle nut. That is, the thickness of the middle nut is different between the upper and lower sides, and by tightening the upper and lower nuts, they are eccentrically fitted to each other to prevent loosening.

  Patent Document 2 discloses a technology for preventing loosening when a panel is fixed using bolts or screws in a panel fixing structure. In claim 4 of this document, shafts of bolts and nuts are provided on the head. Proposals have been made for configurations that are biased toward the center. FIG. 8 shows a screw having a circular head, and an example in which the position of the plus groove is eccentric from the center position of the head.

JP 2002-89533 A JP 2004-324734 A

  The technique of the above-mentioned Patent Document 1 is not eccentric from the center position of a regular polygon (in this example, a regular hexagon) that is the outer edge shape in a cross-sectional shape perpendicular to the rotation axis direction of the nut or bolt. . As understood from FIGS. 1 and 2 of the document, the rotation center of the bolt is not deviated from the outer edge shapes of the bolt head and the nut. Moreover, in order to exhibit the function of preventing looseness, it is necessary to install and install the nuts in order of three types, and it is inevitable that the tightening operation is complicated and requires a long time. Therefore, it is not suitable for bolt tightening work in a steel tower or the like that requires quickness and simplicity.

  Next, in the technique of Patent Document 2, as a specific disclosure, eccentricity in a screw having a circular head with a plus groove is shown, but a shaft portion and screw for a bolt or nut having a regular polygonal head. The eccentricity of the hole is not disclosed. With respect to a screw having a circular head, the positions of plus and minus grooves can be easily decentered, but it is difficult to apply to a bolt having a polygonal cross-sectional shape. In the case of a bolt having a regular polygonal head or a nut having a regular polygonal outer shape, if a shaft part or a screw hole is simply arbitrarily decentered, it is difficult to rotate with a normal tool.

  In addition, what is indicated by the name of the eccentric bolt exists on the Internet, etc., but their configuration is the same as the above-mentioned example, the rotational axis of the head itself is eccentric with respect to the center of the regular polygonal head. Thus, the shaft portion is not formed.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a loosening prevention bolt and a loosening prevention nut capable of accurately preventing loosening due to vibration of a mounting object with a simple structure. is there.

In order to solve the above problem, the loosening prevention bolt according to claim 1 is:
The cross-sectional shape of the head in the direction orthogonal to the rotation axis is a polygonal shape having at least one pair of sides facing substantially parallel, and the center position of the shaft portion is any one of the pairs of facing sides substantially parallel. It is characterized in that it is set to be equidistant from both sides of the pair and to be shifted to any one end side from the center position in the extending direction of the pair of opposing sides.

  According to this configuration, the shaft is formed at a position equidistant from both sides of any one of the substantially parallel opposing sides, so that a normal tool such as a spanner or a wrench can be used. The possibility of rotating work is secured. And the eccentric state of the axial part with respect to a head is obtained by deviating from the center position of the extension direction of the pair of opposing sides to any one end side. As a result, the rotational moment in only one direction of the head can be increased, and loosening due to fine vibration or the like that occurs in the conventional head having a uniform rotational moment can be effectively prevented.

In order to solve the above problem, the loosening prevention bolt according to claim 2 is:
The head cross-sectional shape in the direction orthogonal to the rotation axis has a regular polygonal basic shape having at least one pair of sides facing substantially parallel to each other, and only one pair of the two opposite sides is the other side. A long polygon formed longer than the center position of the shaft portion is equidistant from the two long sides and deviated from the center position in the extending direction of the two long sides to either end side. It is characterized by being set.
In this configuration, the cross-sectional shape of the head itself is modified from a conventional regular polygon. In this configuration, the shaft portion of the bolt is offset toward one of the two long sides of the long polygon, but the center of the shaft portion is set at a position equidistant from the two long sides. Similar to the bolt of claim 1, there is no problem when tightening with a normal tool such as a spanner or a wrench. And since two long sides are installed, it becomes possible to ensure a larger amount of displacement than simply decentering the shaft center in a regular polygonal cross-sectional shape.

  Therefore, the rotational moment in only one direction can be increased, and a larger difference than the rotational moment difference obtained by the uniform rotational moment or the eccentricity within the regular polygon can be secured. The loosening prevention function can be greatly improved. In other words, the amount of eccentricity within the normal regular polygonal shape range is limited, but by using a long polygonal head shape in this way, the function of preventing loosening due to vibration is further improved. Yes.

The loosening prevention bolt according to claim 3 is the loosening prevention bolt according to claim 2,
The cross-sectional shape of the head is a long hexagon in which a regular hexagon is used as the basic shape and only a pair of two opposing sides are elongated, and the central position of the shaft portion is the central position of the regular hexagon as the basic shape. It is characterized by that.

  With this configuration, the shaft portion exists at a position where the distances from the four adjacent sides of the bolt having the regular hexagonal head are common. Therefore, the rotation of the bolt with a wrench or spanner is carried out by attaching it from the outer central direction of the four sides, but the rotation operation of the bolt itself is almost the same as that of a normal regular hexagon head bolt. Can be done with a sense.

The loosening prevention nut according to claim 4 is:
The cross-sectional shape in the direction orthogonal to the rotation axis is a polygonal shape having at least a pair of sides facing substantially parallel, and the center position of the screw hole is the position of any one of the pairs of facing sides substantially parallel. It is characterized in that it is set at an equal distance from each side and deviated from the central position in the extending direction of the pair of opposite sides to any one end side.

  According to this configuration, the screw hole is formed at an equidistant position from any one of the pair of opposing sides of the substantially parallel opposing sides, thereby enabling the possibility of rotating work with a normal tool. Is secured. And the eccentric state of the screw hole with respect to a cross-sectional shape is obtained by deviating from the center position of the extension direction of the pair of opposing sides to any one end side. As a result, the rotational moment in only one direction can be increased, and the function of preventing loosening against micro-vibration can be improved as compared with the conventional screw hole center having a uniform rotational moment.

The loosening prevention nut according to claim 5 is:
A cross-sectional shape in a direction perpendicular to the rotation axis is based on a regular polygon having two sides facing substantially parallel to each other, and only one pair of the two facing sides is longer than the other sides. A long polygonal shape is formed, and the center position of the screw hole is equidistant from the two long sides, and is displaced to any one end side from the central position in the extending direction of the two long sides. It is characterized by being set.
In this configuration, the sectional shape of the nut itself is modified from a conventional regular polygonal one. In this configuration, the screw hole of the nut is offset near the ends of the two long sides of the long polygon, but the center of the screw hole is set at a position equidistant from the two long sides. There is no problem when tightening with a normal tool such as a spanner or wrench. Since the two long sides are set, it is possible to secure a larger displacement amount than simply decentering the rotation center of the shaft portion in the regular polygonal cross-sectional shape.

  Therefore, the rotational moment in only one direction can be increased, and a larger difference than the rotational moment difference obtained by the uniform rotational moment or the eccentricity within the regular polygon can be secured. The loosening prevention function can be greatly improved. That is, the amount of eccentricity within the range of the regular regular polygonal shape is limited, but the function of preventing loosening due to vibration is further improved by using a long polygonal nut cross-sectional shape in this way. ing.

The loosening prevention nut according to claim 6 is the loosening prevention nut according to claim 5,
The cross-sectional shape is a long hexagon in which only one pair of two opposing sides is elongated with the regular hexagon as the basic shape, and the center position of the screw hole is the center position of the regular hexagon as the basic shape It is characterized by that.

  With this configuration, a screw hole is present at a position where the distances from four adjacent sides of a normal regular hexagonal cross-sectional shape are common. Therefore, the nut is rotated by a fastening tool such as a wrench or a wrench by attaching the tool from the center direction outside the four sides. However, the rotation operation of the nut itself is a regular regular hexagon. This can be done with a feeling similar to that of a nut.

  According to the loosening prevention bolt and the loosening prevention nut according to the present invention, there is no hindrance to tightening with a tightening tool such as a spanner or a wrench, and by increasing the rotational moment only in one direction, The function of preventing the bolts and nuts from gradually loosening can be greatly improved.

(A) And (B) is the side view and front view which show the shape of the loosening prevention volt | bolt which concerns on embodiment. (A) And (B) is the side view and front view which show the shape of the loosening prevention nut which concerns on embodiment. It is explanatory drawing of the use condition of the loosening prevention volt | bolt and nut which concern on embodiment. (A) And (B) is the side view and front view which show the structure of the loosening prevention volt | bolt which concerns on embodiment using a long polygonal head. (A) And (B) is the side view and front view which show the structure of the loosening prevention nut which concerns on embodiment using the outer edge shape of a long polygon. (A), (B) and (C) are explanatory views showing an example in which a loosening prevention nut according to an embodiment using a long polygonal outer edge shape is mounted on a cotter bolt and used. (A), (B), and (C) are explanatory drawings of a state in which both a loosening prevention cotter bolt using a long polygonal head and a loosening prevention nut using a long polygonal outer edge shape are used. (A), (B) and (C) are the structure explanatory drawings of the conventional cotter bolt.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, FIGS. 1 and 2 show examples of a loosening prevention bolt and a loosening prevention nut according to the present embodiment. 1A is a side view of a loosening prevention bolt 10 having a head having a regular hexagonal cross-sectional shape (cross-sectional shape in a direction perpendicular to the rotation axis), and FIG. 1B is a front view from the head side. As shown in the figure, the loosening prevention bolt 10 according to the present embodiment is displaced so that the shaft portion 10a approaches the one vertex 10p side of the hexagon from the center position of the regular hexagonal head 10b. That is, the rotation center of the shaft portion 10a is shifted slightly upward in the figure rather than the center position of the regular hexagon.

  However, the rotation center of the shaft portion 10a is set at a position equidistant from each of two substantially parallel facing sides 10c and 10d in the head 10b. Therefore, it is possible to perform a rotating operation with a normal tool. Further, as described above, the center of rotation is deviated from the center in the extending direction of the pair of opposing sides 10c and 10d to one end side, in this embodiment, to the apex 10p side. Therefore, a large rotational moment in only one direction in the head 10b is set. That is, the length from the rotation center of the head 10b to the apex m is longer than the lengths to the apexes and sides of other heads. As a result, it is possible to improve the function of preventing loosening against micro-vibration or the like as compared with the conventional head having a uniform rotational moment.

  2A is a side view of the loosening prevention nut 20 having a regular hexagonal cross-sectional shape (cross-sectional shape in a direction perpendicular to the rotation axis), and FIG. 2B is a front view from the rotation axis direction. As shown in the drawing, the loosening prevention nut 20 according to the present embodiment is displaced so that the screw hole 20a approaches the one vertex 20p side of the hexagon from the center position of the regular hexagonal cross section. That is, the rotation center of the loosening prevention nut 20 is shifted slightly upward in the figure rather than the center position of the regular hexagon.

  However, the rotation center of the loosening prevention nut 20 is set at a position equidistant from each of two substantially parallel opposing sides 20c and 20d in the outer edge shape of the loosening prevention nut 20. Therefore, it is possible to perform a rotating operation with a normal tool. Further, as described above, the pair of opposed sides 20c and 20d is deviated from the center in the extending direction to any one end side, in this embodiment, to the apex 20p side. Accordingly, the rotational moment in only one direction of the nut 20 can be increased. That is, the length from the rotation center of the nut 20 to one vertex m of the nut 20 is longer than the length to the vertex or side of the other head. As a result, it is possible to improve the function of preventing loosening against micro-vibration or the like as compared with the conventional nut shape having a uniform rotational moment.

  FIG. 3 shows an example in which the members 100 and 200 are fastened by using the loosening prevention bolt 10 and the loosening prevention nut 20 together. As shown in the drawing, the loosening prevention bolt 10 is installed with the apex m, which is the side with the long rotational moment, positioned downward, and the anti-loosening nut 20 also rotates to the place where the apex m, which is the side with the long rotational moment, is positioned below. I am letting. As a result, since the loosening prevention bolt 10 and the loosening prevention nut 20 are heavy portions and the end portion having a long rotational moment is positioned below, loosening due to micro vibrations can be effectively prevented. For example, when the members 100 and 200 are attachment members such as attachment of various members to a steel tower of a high-voltage power transmission line, it is possible to accurately prevent loosening of bolts and nuts as fastening members due to slight vibration generated in the steel tower due to wind or the like. It can be carried out.

  FIG. 4 shows another embodiment of another loosening prevention nut. As shown in the figure, the loosening prevention bolt 30 has a cross-sectional shape in a direction orthogonal to the axial direction of the head 30a, not a regular hexagon, but a long hexagon. That is, with a regular hexagon as a basic shape (x), only a pair of opposing sides 30d and 30e that are substantially parallel to each other are formed longer than the other sides.

  And in this Embodiment, the center of the rotating shaft of the axial part 30b is set to the center position of the regular hexagon X shown by the wavy line. Therefore, the long hexagonal long sides 30d and 30e are set to positions that are omnidirectional from the center position in the extending direction. In this way, by making only one opposing two sides of the regular hexagon longer than the other sides, the length from the center of the shaft 30b to the outer edge of the head 30a is not uniform, and the side with the longer rotational moment And the short side has arisen.

  With this configuration, similarly to the operation according to the embodiment shown in FIGS. 1 to 3, it is possible to accurately prevent loosening due to the occurrence of minute vibrations at the bolt fastening portion. Furthermore, since the position of the shaft portion 30b is set to the original center position of the regular hexagon X, the two long sides 30d and 30e of the head 30a and the upper sides 30f and 30g in the figure sandwiched between them are The length from each side to the rotation center of the shaft portion 30b is the same. Accordingly, the upper portion of the loosening prevention bolt 30 in the figure has the same configuration as that of the bolt having an original regular hexagonal head, and a bolt rotating tool such as a spanner or a wrench is used from the upper portion of the figure. The bolt rotation operation to be performed can be performed with an operation feeling similar to that of a bolt having a regular hexagonal head.

  In addition, by making the head shape into a long polygon instead of a regular polygon in this way, a displacement length larger than the case where the position of the shaft portion 30b is centric within the range of the regular polygon head shape is obtained. It is possible to secure a larger difference in rotational moment. As a result, the contact area of the head 30a with the object to be fastened also increases only on the apex m side, and the effect of preventing loosening due to slight vibration is further improved.

  FIG. 5 shows another embodiment of another loosening prevention nut. As shown in the drawing, the loosening prevention nut 40 has a cross-sectional shape in a direction orthogonal to the rotation axis direction, not a regular hexagon but a long hexagon. That is, a regular hexagon is used as a basic shape (y), and only a pair of opposing sides 40d and 40e are formed longer than the other sides.

  And in this Embodiment, the center of the rotating shaft of the screw hole 40a is set to the center position of the regular hexagon Y shown by the wavy line. Accordingly, the long hexagonal two sides 40d and 40e are set at positions deviated from the center position. In this way, by making only one opposite two sides of the regular hexagon longer than the other sides, the length from the center of the screw hole 40a to the outer edge of the loosening prevention nut 40 is not uniform, and the rotational moment The long side and the short side are generated.

  Therefore, as in the case of the loosening prevention bolt 30 described with reference to FIG. 4 above, the center position of the screw hole 40a (the rotation center of the nut) is the two long sides 40d and 40e of the nut 40 and the upper side in the figure sandwiched between them. The lengths from the sides 40 f and 40 g to the rotation center of the nut 40 are the same. Thereby, as in the case of the bolt shown in FIG. 4, the nut rotation operation performed using the nut rotating tool from the upper side in the drawing can be performed with the same operation feeling as a nut having a regular hexagonal outer edge shape.

  In addition, it is possible to secure a larger displacement length than the case where the position of the screw hole 40a is displaced within the range of the regular polygonal nut shape, and to ensure a larger difference in rotational moment. The effects such as an increase in only the apex m side of the contact area to the fastening object can be obtained as in the case of the bolt.

  6A, 6B and 6C show an embodiment in which the present invention configuration shown in FIG. 5 is applied to a nut attached to the conventional cotter bolt shown in FIG. In addition, the same code | symbol is shown to the element similar to FIG. As shown in the figure, in this embodiment, a cotter bolt 54 is inserted into the through hole of the combined overhead wire fittings 50 and 52, and a loosening prevention nut 70 is attached to the cotter bolt 54. In order to prevent the nut 70 from falling off, a pin hole 58 is formed in the shaft portion 54a of the bolt 54. The split pin 60 is inserted into the pin hole 58, and the tip 60a is on both sides of the shaft portion 54a. (Fig. 3C).

  In the present embodiment, the loosening prevention nut 70 (the center of rotation) is omnidirectional from the center position of the nut 70a, as clearly understood in FIG. ing. That is, as described above, the pair of parallel opposing sides 70d and 70e of the outer edge portion of the nut 70 are formed longer than the lengths of the other sides, and the shaft portion 70 has the sides 70d, 70e, and 70f of the head 70. , 70 g is set at an equal distance from each side. That is, the rotation center position of a virtual regular hexagon including these four sides is set, and is centered slightly upward in the figure from the center position in the length direction of the long sides 70d and 70e. Therefore, the length from the rotation center of the nut 70 to the vertex m is longer than the length to the other vertex. As a result, a difference is generated in the rotational moment of the nut 70, and the loosening rotation against fine vibration or the like can be prevented by finishing the fastening operation so that the vertex m comes to the lower position.

  FIGS. 7A, 7B, and 7C show an embodiment in which the present invention configuration is applied to both the conventional cotter bolt and nut shown in FIG. In addition, the same code | symbol is shown to the element similar to FIG. As shown in the drawing, not only the loosening prevention nut 70 but also the cotter bolt is configured as a loosening prevention cotter bolt 80.

  As shown in the figure, the shaft 80b (rotation center) of the loosening prevention cotter bolt 80 is universal from the center position of the head 80b, as clearly understood in FIG. Is ranked. That is, as described above, the pair of parallel opposing sides 80d and 80e of the outer edge portion of the bolt 80 are formed longer than the lengths of the other sides, and the shaft portion 80b has the sides 80d, 80e, and 80f of the head 80a. , 80 g are set at an equal distance from each side. That is, the rotation center position of a virtual regular hexagon including these four sides is set, and is centered slightly upward in the figure from the center position in the length direction of the long sides 80d and 80e.

  Therefore, the length from the rotation center of the shaft 80b of the bolt 80 to the vertex m is longer than the length to the other vertex. As a result, a difference is generated in the rotational moment of the nut 70, and the loosening rotation against fine vibration or the like can be prevented by finishing the fastening operation so that the vertex m comes to the lower position. In this way, by applying a long hexagonal shape to both bolts and nuts, and thereby shifting the rotation center from the center position of the outer edge shape, it is possible to more reliably prevent the fastening portion from loosening. it can.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible within the range of the summary of invention. For example, in the above embodiment, a bolt and a nut having a hexagonal head have been shown as an example. However, a polygonal head or nut having parallel sides facing each other in a cross-sectional outer edge shape in a direction perpendicular to the rotation axis ( For example, the present invention can be applied to a rectangular shape.

  In the embodiment shown in FIG. 4 to FIG. 7, the position of the shaft portion and the screw hole in the long hexagon is the center position of the virtual regular hexagon as described above. If the position is equidistant from the side, it can be set closer to the end portion with a shorter rotational moment.

10 Loosening prevention bolt 10a Shaft portion 10b Head 20 Loosening prevention nut 20a Screw hole 30 Long hexagon head loosening prevention bolt 30d, 30e Long side 40 Long hexagonal shape loosening prevention nut 40d, 40e Long side 70 Mounted on cotter bolt Long hexagonal nut 80 Loosening prevention cotter bolt with long hexagonal head

Claims (6)

The cross-sectional shape of the head in the direction perpendicular to the rotation axis is a polygonal shape having at least one pair of sides facing each other substantially in parallel.
The center position of the shaft portion is equidistant from both sides of any one of the substantially parallel opposing sides, and any end side from the central position in the extension direction of the pair of opposing sides. A loosening prevention bolt characterized in that it is set to be biased. The head cross-sectional shape in the direction orthogonal to the rotation axis has a regular polygonal basic shape having at least one pair of sides facing substantially parallel to each other, and only one pair of the two opposite sides is the other side. It is a long polygon formed longer than,
Looseness characterized in that the center position of the shaft portion is set at an equal distance from the two long sides and deviated from the center position in the extending direction of the two long sides to either end side. Prevention bolt. The head cross-sectional shape is a long hexagon having a regular hexagon as the basic shape and having a pair of opposing two sides elongated,
3. The loosening prevention bolt according to claim 2, wherein a center position of the shaft portion is a center position of a regular hexagon as the basic shape. The cross-sectional shape in the direction orthogonal to the rotation axis is a polygonal shape having a pair of sides facing at least substantially parallel,
The center position of the screw hole is equidistant from each of the pair of opposing sides of the substantially parallel opposing sides, and any end side from the central position in the extending direction of the pair of opposing sides. A loosening prevention nut characterized in that it is set to be biased. A cross-sectional shape in a direction perpendicular to the rotation axis is based on a regular polygon having two sides facing substantially parallel to each other, and only one pair of the two facing sides is longer than the other sides. It is a long polygon formed long,
Looseness characterized in that the center position of the screw hole is set at an equal distance from the two long sides and deviated from the center position in the extending direction of the two long sides toward either end. Prevention nut.   The cross-sectional shape is a long hexagon in which only one pair of two opposing sides is elongated with the regular hexagon as the basic shape, and the center position of the screw hole is the center position of the regular hexagon as the basic shape The loosening prevention nut according to claim 5, wherein the nut is a loosening prevention nut.

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