Description BOLTSTRUCTURE,ANDBOLTANDNUTASSEMBLY STRUCTURE Technical Field [1] The present invention relates to a bolt structure, and a bolt and nut assembly structure which can achieve unification by being fastened regardless of directions of their screw threads, which can be completely prevented from being unfastened due to stronger strength for looseness-prevention, and also which can make process or manufacture and fastening assembly easier even with simple construction. Background Art [2] Conventionally, as means for fastening an object and an object in various machine apparatus, various structures, various constructions, etc., bolts are broadly used, and various bolts have been developed. Screw fastening using such bolts can be commonly achieved by conjoining a male thread of a bolt into a female thread of a nut, etc. Although screw threads are classified into left handed threads and right handed threads according to the rotational direction for conjoining them, commonly right handed threads are broadly employed, but if necessary, left handed threads are also employed. [3] On the other hand, in order to prevent looseness in bolt-fastening due to vibration, etc., a method of fastening a bolt using a lock nut is broadly employed. Also, various structures of bolts and/or nuts are developed for such looseness prevention. For example, a nut-looseness prevention device is disclosed in Korean Utility Model Laid- open Publication No. 20-1998-0060388, wherein an elastic bush intervenes between two fastened nuts so as for a bolt and two nuts not to be loosened after being joined for fastening members in various machine apparatus or structures, and wherein two fastened nuts differ in a fastening direction, or a protrusion of a wave shape is formed on the contact surfaces between two nuts with a looseness prevention plate installed on the intervened elastic bush, and thus is invented so that a fastening force can be maintained by an elastic force, thereby preventing looseness of the fastening portion without use of additional adhesive, etc., for looseness prevention, and so that the fastening state at the constructed time can be maintained durable for a long time, and if necessary, release or rejoining can be also performed conveniently and easily, thereby being very useful and maintaining reliability of the fastening state perfectly. [4] In addition, such similar construction is disclosed on Japanese Patent Laid-open Publication No. H5-71513(1993.3.23), Japanese Patent Laid-open Publication No. H6- 173929(1994.6.21), Japanese Patent Laid-open Publication No. H7-4418(1995.1.10), etc. Disclosure of Invention Technical Problem [5] However, each construction described above is designed in a manner such that a bolt has different diameters in screwing threads, or a female screw portion is formed inside the end of the screw portion of a bolt, etc., thereby having problems that machining is complex and difficult, and that a fastening force becomes weak at a screw portion in which an external diameter is smaller. [6] Furthermore, another problem is that the structure becomes more complicated in such construction as having different external diameters in screws because the two nuts are designed to be in contact with each other at a fastening operation. [7] Still another problem is that a conventional bolt employs one of a right-handed screw thread or a left-handed screw thread, and therefore, cannot be fastened into a female screw portion of a different-handed thread even if their pitches are the same. [8] Accordingly, the present invention is made in order to solve the above problems, and one object of the present invention is to provide a bolt structure, and a bolt and nut assembly structure which can achieve unification by fastening a bolt and a nut or a female threaded hole regardless of directions of their screw threads, which can be completely prevented from being unfastened due to stronger strength for looseness prevention, and also which can make process or manufacture and fastening assembly easier. Technical Solution [9] To accomplish the object of this invention, a bolt structure with a male thread portion is provided in accordance with one embodiment of the present invention, on which screw threads are formed to be fastened to a nut or a female threaded hole, wherein said male thread portion has a right-handed thread and a left-handed thread formed on the same external diameter with the male thread portion in an overlap con¬ figuration so that the male thread portion can be fastened to the nut or the female threaded hole simply by rotating the male thread portion in any one direction of a right-hand direction and a left-hand direction even if the nut or the female threaded hole has a thread of any one direction of the right-hand direction and the left-hand direction. [10] In this case, when one thread of the right-handed thread and the left-handed thread is used as one for a fastening nut, the one thread for the fastening nut can be formed toward the end of the bolt including at least a length of a fastening thread portion to which a first nut for fastening is fastened, and the other thread of the right-handed thread and the left-handed thread, as a reverse direction thread for a looseness prevention nut, can be formed on the same external diameter with said one thread in an overlap configuration toward the end of the bolt at least from the rear of the length of the fastening thread portion excluding the length of the fastening thread portion, a second nut for looseness prevention being fastened in the reverse direction to the first nut so as to be further fastened when the second nut is rotated by friction, etc., together with the first nut to be rotated in the direction of release by vibration, etc., and so as to perfectly prevent looseness of the first nut. [11] Furthermore, when the right-handed thread is one for fastening, a pitch and/or a lead angle of ridges or grooves of thread in the left-handed thread may be the same as, or larger than, those in the fastening thread. [12] Still furthermore, the present invention is to provide a bolt and nut assembly structure in which two nuts of a first nut for fastening and a second nut for looseness prevention are fastened to a bolt in order to prevent looseness of the first nut fastened to the male thread portion of the bolt: wherein said bolt has a thread for a fastening nut(referred to as a fastening-nut thread) and to which a female thread of the first nut is fastened, and a reverse direction thread to the thread for the fastening nut, said fastening-nut thread being formed toward the end of the bolt including at least a length of a fastening thread portion to which the first nut is fastened, and the reverse direction thread being formed on the same external diameter with said fastening-nut thread in an overlap configuration toward the end of the bolt at least from the rear of the length of the fastening thread portion excluding the length of the fastening thread portion; wherein the first nut is fastened to the fastening-nut thread of the bolt at the length of the fastening thread portion; and, wherein the second nut is fastened in the reverse direction thread of the bolt at the rear of the first nut so as to be further fastened when the second nut is rotated by friction, etc., together with the first nut to be rotated in the release direction by vibration, etc., and so as to perfectly prevent looseness of the first nut. [13] Still furthermore, the present invention is to provide a bolt and nut assembly structure in which a nut for fastening is fastened to a thread for a fastening nut formed at least at the end of a bolt: wherein said fastening nut is a double purpose nut both for fastening and for looseness prevention, said nut having a thread formed for mating engagement with the fastening-nut thread and a reverse direction thread to the thread formed in an overlap configuration with the thread; wherein said bolt has a reverse direction thread to the fastening-nut thread in an overlap configuration with the fastening-nut thread in the portion of the fastening-nut thread; and, wherein, in the thread portion of the bolt to pass through, and protrude from, bolt holes of parent members, parent member and connecting plate member, etc., the double purpose nut is rotated a little in the reverse direction within the range not to be separated from the fastening-nut thread and is fastened to the reverse direction thread, after the double purpose nut is fastened to the fastening-nut thread in the fastening direction of the fastening-nut thread to a position in which the double purpose nut can be also fastened to the reverse direction thread by the reverse direction rotation, thereby further increasing a fastening force even when the double purpose nut is rotated in any direction by vibration, etc., and perfectly preventing looseness of the double purpose nut. Advantageous Effects [14] By virtue of the bolt structure in accordance with the embodiments of the present invention described above, since a right-handed thread and a left-handed thread are formed on the same external diameter with the bolt in an overlap configuration, the bolt can be fastened to a female thread of any direction of a right-hand direction and a left-hand direction, and in case of looseness prevention, manufacture of the bolt and fastening assembly become easier concurrently with perfectly preventing looseness of the first nut. [15] Further, by virtue of the bolt and nut assembly structure in accordance with the double purpose nut of the present invention described above, looseness can be prevented only by fastening one nut, and moreover a length of the thread portion of the bolt and space of the bolt and nut assembly structure can decrease with easier manu¬ facturing of the bolt. Brief Description of the Drawings [16] Figures 1 to 3 are schematical front views of bolt structures according to em¬ bodiments of the present invention. [17] Figures 4 to 6 are schematical sectional views illustrating the fastening process and a fastened state using the bolt of Fig. 1. [18] Figure 7 is a schematical sectional view illustrating a fastened state using the bolt of Fig. 2. [19] Figure 8 is a schematical sectional view illustrating a fastened state using the bolt of Fig. 3. [20] Figure 9 is a schematical sectional view illustrating a fastened structure of a bolt and a nut for looseness prevention according to another embodiment of the present invention. [21] Figures 10 to 12 are schematical front views of bolt structures according to still another embodiments of the present invention. [22] Figures 13 and 14 are schematical sectional views illustrating examples of structures to fasten a first member and a second member using the bolt of the present invention. [23] Figures 15 and 16 are schematical sectional views illustrating the fastening process and a fastened state of a parent member and a parent member with an overlapping plate using the bolt of Fig. 10. [24] Figure 17 is a schematical sectional view illustrating a fastened state using the bolt of Fig. 11. [25] Figure 18 is a schematical sectional view illustrating a fastened state using the bolt of Fig. 12. [26] Figure 19 is a schematical sectional view illustrating another example of a fastened structure of a bolt and a nut for looseness prevention according to further another embodiment of the present invention. [27] Figure 20 is a schematical sectional view of a fastened state similar to that of Fig. 17 illustrating a state in which prominences and depressions are formed on the contact surfaces between a first nut and a second nut according to still further another embodiment of the present invention, and Figure 21 is a plan view of the contact surface of the nut. Mode for the Invention [28] Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. [29] In this specification, the expression of "for fastening" means to be first fastened and for achieving a fastening purpose mainly, and the expression of "for preventing looseness" or "for looseness prevention" means to be secondly fastened and for achieving a purpose of preventing looseness of the first fastened state. [30] In Figs. 1 to 9, a thread portion for fastening and a thread portion for looseness prevention are referred to as each portion to which a first nut(41) for fastening and a second nut(42, 43 or 44) for looseness prevention are fastened among a male thread portion(lll, 121 or 131) of Figs. 10 to 12, and terms of a fastening-nut thread(13, 23 or 33) and a reverse direction thread(14, 24 or 34) are similarly used in Figs. 1 to 9 instead of terms of a right-handed thread and a left-handed thread. [31] In Figs. 1 to 3 and 10 to 12, structures according to embodiments of the present invention are shown as schematic front views, and in Fig. 4, schematical sectional view of the fastening process is illustrated using the bolt of Fig. 1, with fastened states using the bolts illustrated in Figs. 5 to 8. [32] Each bolt(10, 20 or 30) shown in Figs. 1 to 3 has a non-thread portion(15, 25 or 35) formed by a non-thread portion length(X) below a bolt head, and the fastening-nut thread(13, 23 or 33) formed toward the end of the bolt(10, 20 or 30) including at least a fastening thread portion length(Y) to which the first nut(41) for fastening is fastened, that is, over at least a fastening thread portion length(Y) and a looseness prevention thread portion length(Z). At least by a looseness prevention thread length(Z), a reverse direction thread(14, 24 or 34) is formed in the reverse direction to, on the same external diameter with, and in an overlap configuration with, the fastening-nut thread(13, 23 or 33). It is preferred that the non-thread portion length(X) of the non- thread portion(15, 25 or 35) is the same with, or smaller than a total width(W, Wa or Wb) of fastened members in Figs 4 to 9. Although a position at which the fastening thread portion length(Y) and the looseness prevention thread portion length(Z) are joined is not decided exactly considering the total width(W, Wa or Wb) of the fastened members and a height of the first nut(41), allowance for the position is increased by providing a chamfer on a female threaded hole at the contact surface between the first nut(41) and the second nut(42, 43 or 44) or inserting a washer into the contact surface. [33] Thus, in the looseness prevention thread portion length(Z) on which the fastening- nut thread(13, 23 or 33) and the reverse direction thread(14, 24 or 34) are formed in an overlap configuration, grooves of the fastening-nut thread(13, 23 or 33) or the reverse direction thread(14, 24 or 34) are constant, while thread ridges of fastening-nut thread(13, 23 or 33) or the reverse direction thread(14, 24 or 34) become shapes cut by grooves of each other thread. That is, ridges and grooves are formed in normal shapes in a junction(A or E) of the ridges of the fastening-nut thread(13, 23 or 33) and the reverse direction thread(14, 24 or 34) and a junction(C) of the grooves of the fastening- nut thread(13, 23 or 33) and the reverse direction thread(14, 24 or 34), while the ridges of one of the fastening-nut thread(13, 23 or 33) and the reverse direction thread(14, 24 or 34) are cut by the grooves of the other of the fastening-nut thread(13, 23 or 33) and the reverse direction thread(14, 24 or 34) in ajunction(B) of the ridges of the fastening-nut thread(13, 23 or 33) and the grooves of the reverse direction thread(14, 24 or 34) or in a junction(D) of the grooves of the fastening-nut thread(13, 23 or 33) and the ridges of the reverse direction thread(14, 24 or 34). Between the above junctions(A,E), ridges of the fastening-nut thread(13, 23 or 33) are cut by volumes overlapped by the grooves of the reverse direction thread(14, 24 or 34). Thus, in case pitches(Pb) are the same between the ridges or the grooves of the fastening-nut thread(13, 23 or 33) and the reverse direction thread(14, 24 or 34) as in Fig. 2, the ridges and the grooves appear in a diamond shape in a front view and remaining shapes of each ridges thereof are the same with each other, while, in case pitches(Pa,Pc) of the grooves of the reverse direction thread(14, 24 or 34) are twice pitches of the ridges of the fastening-nut thread(13, 23 or 33) as in Figs. 1 and 3, ridges of the fastening-nut thread(13, 23 or 33) have different remaining shapes according to positions as shown in various shapes in front views as in Figs. 1 and 3. As in Figs. 5, 6 and 8, every other ridge between adjoining female threads is completely cut, becoming simple cylinder shape. [34] Meanwhile, although the non-thread portion(15, 25 or 35) is included in these em- bodiments, only a thread portion can be formed with no non-thread portion(15, 25 or 35) as in Figs. 10 to 12. Also, the non-thread portion(15, 25 or 35) and the fastening- nut thread(13, 23 or 33) have almost similar external diameters, respectively, but can be formed on different external diameters. [35] Furthermore, although the reverse direction thread(14, 24 or 34) has the same external diameter with the fastening-nut thread(13, 23 or 33) in Figs. 1 to 3, the grooves may have different depths. Although the reverse direction thread(14, 24 or 34) has the same pitch with the fastening-nut thread(13, 23 or 33) in the ridges or the grooves, each lead angle(L) can be different in Figs. 1 and 3. If the lead angle(L) increases, the ridges of the fastening-nut thread(13, 23 or 33) are remained more and a contact surface area of the second nut(42 or 44) per one rotation is increased although a later-mentioned fastening force of the second nut(42, 43 or 44) and the reverse direction thread(14, 24 or 34) will be decreased as in case the pitch of the grooves of the reverse direction thread(14, 24 or 34) is increased. In order to fasten the second nut(42 or 44) by the same number of rotation, a height(H2) of the second nut(44) in Fig. 8 should become increased more than a height(Hl) of the second nut(42) in Fig. 5. [36] However, in case of decreasing the pitch of the ridges(grooves) of the reverse direction thread(14, 24 or 34) less than in the fastening-nut thread(13, 23 or 33), it is undesirable because the ridges of the fastening-nut thread(13, 23 or 33) are removed or cut too much, thereby exerting an influence on the fastening of the second nut(42, 43 or 44) for looseness prevention. [37] After the bolt constructed as specified above passes through each bolt hole of a parent member(50) and connecting plate members(51,52), and the first nut(41) is fastened to the thread portion of the bolt to protrude from the bolt holes in the reverse side of a bolt head as in Fig. 4, the second nut(42, 43 or 44) for looseness prevention is fastened to the reverse direction thread(14, 24 or 34) of the bolt as in Figs. 5, 7 and 8, and thus the fastening is completed. [38] Thereafter, although the first nut(41) is about to rotate a little in the release direction by vibration, etc., the rotation of the first nut(41) in the release direction rotates the second nut(42, 43 or 44) in the fastening direction by friction, etc., thereby the second nut(42, 43 or 44) being further fastened and looseness of the first nut(41) being perfectly prevented. [39] Although an embodiment for fastening the parent member(50) and the parent member(50) with the connecting plate members(51,52) is illustrated and explained above, an embodiment for fastening the parent member(50) and the parent member(50) in an overlap configuration without the connecting plate members(51,52) can be realized similarly. Further, in case the parent member(50) is fastened directly to a plate member(53) with a female thread without the first nut(41) as in Fig. 6, the female thread is formed through the plate member(53) and the fastening-nut thread(13, 23 or 33) in the fastening thread portion length(Y) of the bolt(lθ) is fastened to the female thread, the second nut(42, 43 or 44) for looseness prevention being fastened to the reverse direction thread(14, 24 or 34) in the rear looseness prevention thread portion length(Z) protruded in the rear and looseness being perfectly prevented as described above. The female threaded plate member(53) may be another parent member, and in case of being fastened thus, an external diameter of the non-thread portion length(X) is generally formed largely. Therefore, the foregoing first nut(41) for fastening should be interpreted as a concept including the female threaded plate member(53). [40] Fig. 9 is a schematical sectional view illustrating structures of a bolt and a nut for looseness prevention according to another embodiment of the present invention with their fastened structure. [41] Fig. 9 relates to the fastened structure of a bolt and a nut for looseness prevention for fastening the parent member(50) and the parent member(50), the parent member(50) and the connecting plate members(51,52), etc., by fastening the first nut(41) to a fastening-nut thread(61) formed at the end of the bolt. The concept of a fastening thread portion length(Y) of the bolt(10,20,30) on which the fastening-nut thread(13, 23 or 33) is formed only, and a looseness prevention thread portion on which the reverse direction thread(14, 24 or 34) is formed together, and the concept of the above-mentioned first and second nuts(41 and 42, 43 or 44) each for fastening and looseness prevention are realized in one thread portion and one nut. [42] That is, the nut for fastening in Fig. 9 is a double purpose nut(70) both for fastening and for looseness prevention, in which a female thread is formed for mating engagement with the fastening-nut thread(61) and a reverse direction thread to the female thread is formed in an overlap configuration with the female thread on the same internal diameter of the nut(70), and the bolt in Fig. 9 is a bolt(60) on which a reverse direction thread(62) to the fastening-nut thread(61) is formed in an overlap con¬ figuration and on the same external diameter with the fastening-nut thread(61) in the portion of the fastening-nut thread(61). After the bolt(60) constructed as specified above passes through each bolt hole of a parent member(50) and connecting plate members(51,52), etc., the double purpose nut(70) is fastened to the thread portion of the bolt(60) protruded opposite to a bolt head. In fastening, the double purpose nut(70) is fastened to the fastening-nut thread(61) in the fastening direction of the fastening-nut thread(61) to a position in which the double purpose nut(70) can be also fastened to the reverse direction thread(62) by the reverse direction rotation. Then, the double purpose nut(70) is rotated a little in the reverse direction within the range not to be separated from the fastening-nut thread(61) and is fastened to the reverse direction thread(62). At this time, it is required to fasten the double purpose nut(70) in the reverse direction with an addition of a force, because the fastening force is further increased. Since a fastening force is further increased even if the double purpose nut(70) is rotated in any direction by vibration, etc., the fastening is realized by only the double purpose nut(70) and looseness of the double purpose nut is perfectly prevented. [43] The above-mentioned bolt(10,20,30,60), the first nut(41) for fastening, the second nut(42, 43 or 44) for looseness prevention, the double purpose nut(70) for fastening and for looseness prevention can be changed within the design range according to various thread kinds, such as the thread line number, the thread ridge shapes, the thread parallel or its inclined degree, etc., except the above-mentioned constructions, and in case of employing a washer and even in case the non-thread portion length(X) is formed a little longer than the total width(W,Wb) of the unfastened members, the first nut(41) and the second nut(42, 43 or 44) can be fastened, and the general technique about threads can be adapted or changed within the scope of the present invention besides the above-mentioned technical principles of the present invention. [44] Additionally, a bolt(10, 20 or 30), on which a right-handed thread and a left-handed thread are formed on the same external diameter in an overlap configuration, can be fastened to the nut or the female threaded hole simply by rotating the bolt(10, 20 or 30) in any one direction of a right-hand direction and a left-hand direction even if the female thread is of any one direction of the right-hand direction and the left-hand direction. Also, in case two nuts are fastened for looseness prevention, the two nuts are fastened in the reverse directions to each other, thereby preventing looseness of the nuts more effectively. [45] Furthermore, Figs. 10 to 12 illustrate, as schematical front views, a structure of bolt(110, 120 or 130) according to still another embodiments of the present invention, respectively, and Figs. 13 to 14 as schematical sectional views illustrate examples of structures to fasten a first member and a second member using the bolt. In Fig. 15, the fastening process is shown using the bolt of Fig. 10, and in Figs. 16 to 18, a schematical sectional view of a fastened state using the above-mentioned bolts is il¬ lustrated, repectively. [46] Referring to Figs. 10 to 21, terms of a right-handed thread(13, 23 or 33) and a left- handed thread(14, 24 or 34) are similarly used instead of terms of a fastening-nut thread(13, 23 or 33) and a reverse direction thread(14, 24 or 34) with same reference numerals. [47] In case of having no strength problem, etc., a bolt(l 10, 120 or 130) shown in Figs. 10 to 12 has a male thread portion(l 11, 121 or 131) below a bolt head without a non- thread portion(15, 25 or 35), differently from that having the non-thread portion(15, 25 or 35), but if necessary, the non-thread portion(15, 25 or 35) can be formed. [48] The male thread portion(l 11, 121 or 131), as shown in Figs. 10 to 12 according to the present invention, has a left-handed thread(14, 24 or 34) and a right-handed thread(13, 23 or 33) formed on the same external diameter in an overlap configuration so that the bolt can be fastened by rotating it in any one direction of the right-hand direction and the left-hand direction and can be released by rotating it in the other direction, even if a female thread of a female threaded hole(80a or 80b) in Figs. 13 and 14, or a female thread of a first nut(41) or a second nut(42, 43 or 44) in Figs. 15 to 19 is any one of the left-handed thread(14, 24 or 34) and the right-handed thread(13, 23 or 33). [49] Although the left-handed thread(14, 24 or 34) and the right-handed thread(13, 23 or 33) of the male thread portion(lll, 121 or 131) have the same diameter in the grooves, the external diameters are circumferentially different from one the other because the ridges have shapes cut by grooves of each other's thread. That is, ridges and grooves are formed in normal shapes in a junction(A,E) of the ridges of the right-handed thread(13, 23 or 33) and the left-handed thread(14, 24 or 34) and a junction(C) of the grooves of the right-handed thread(13, 23 or 33) and the left-handed thread(14, 24 or 34), while the ridges of one of the right-handed thread(13, 23 or 33) and the left- handed thread(14, 24 or 34) are cut by the grooves of the other one of the right-handed thread(13, 23 or 33) and the left-handed thread(14, 24 or 34) in a junction(B) of the ridges of the right-handed thread(13, 23 or 33) and the grooves of the left-handed thread(14, 24 or 34) or in a junction(D) of the grooves of the right-handed thread(13, 23 or 33) and the ridges of the left-handed thread(14, 24 or 34). Between the above junctions(A,E), ridges of the right-handed thread(13, 23 or 33) are cut by volumes overlapped by the grooves of the left-handed thread(14, 24 or 34). Thus, in case pitches(Pb) are the same between the ridges or the grooves of the right-handed thread(13, 23 or 33) and the left-handed thread(14, 24 or 34) as in Fig. 11, the ridges and the grooves appear in a diamond shape in a front view and remaining shapes of each ridges thereof are the same with each other, and thus the fastening force of the first nut(41) and the second nut(43) are the same in case each has the same height as in Fig. 17. [50] Furthermore, in case pitches(Pa,Pc) of the grooves of the left-handed thread(14, 24 or 34) are twice pitches of the ridges of the right-handed thread(13, 23 or 33) as in Figs. 10 and 12, ridges of the right-handed thread(13, 23 or 33) have different remaining shapes according to positions as shown in various shapes in front views as in Figs. 10 and 12. As in Figs. 14, 16 and 18, every other ridge between adjoining female threads is completely cut, becoming simple cylinder shape. [51] Moreover, although the left-handed thread(14, 24 or 34) has the same external diameter with the right-handed thread(13, 23 or 33) in Figs. 10 to 12, the grooves may have different depths. Although the left-handed thread(14, 24 or 34) has the same pitch with the right-handed thread(13, 23 or 33) in the ridges or the grooves, each lead angle(L) can be different in Figs. 10 and 12. If the lead angle(L) increases, the ridges of the left-handed thread(13, 23 or 33) are remained more and a contact surface area of the second nut(42 or 44) per one rotation is increased although a later-mentioned fastening force of the second nut(42, 43 or 44) to the left-handed thread(14, 24 or 34) will be decreased as in case the pitch of the grooves of the left-handed thread(14, 24 or 34) is increased. In order to fasten the second nut(42 or 44) by the same number of rotation, a height(H2) of the second nut(44) in Fig. 18 should become increased more than a height(Hl) of the second nut(42) in Fig. 16. However, because the strength of looseness prevention in the second nut as a lock nut in common is stronger than in the conventional lock nut, the height of the second nut can be largely decreased compared with the conventional design height. [52] However, in case of decreasing the pitch of the ridges(grooves) of the left-handed thread(14, 24 or 34) less than in the right-handed thread(13, 23 or 33), it is undesirable becaus the ridges of the right-handed thread(13, 23 or 33) are removed or cut too much, thereby exerting an influence on the fastening such as lowering the fastening force of the second nut(42, 43 or 44) for looseness prevention. [53] In order to join and fix a first member(80) and a second member(81), the bolt(l 10, 120 or 130) constructed as specified above can be fastened to the female threaded hole(80a or 80b) regardless of the thread direction of the female threaded hole(80a or 80b) formed on the first member(80) as in Figs. 13 and 14. Although not shown, a through hole can be provided for the first member(80) as in the second member(81), and the first member(80) and the second member(81) can be fastened by the first nut(41) and/or the second nut(42) in the similar manner to that in Fig. 14 or Fig. 16. Furthermore, as in Figs. 15 to 18, the first nut(41) and/or the second nut(42, 43 or 44) can be fastened to the end of the bolt protruded from the bolt holes opposite to a bolt head after passing through each bolt hole of a parent member(50) and connecting plate members(51,52). [54] In Figs. 15 to 18, after the first nut(41) is fastened to the bolt by any one of the right-handed thread(13, 23 or 33) and the left-handed thread(14, 24 or 34), the second nut(42, 43 or 44) can be fastened to the other one of the right-handed thread(13, 23 or 33) and the left-handed thread(14, 24 or 34) even in any one direction of the same or different directions according to the direction of the thread thereof as in Figs. 16, 17 and 18. As in Fig. 14, where the female threaded hole(80b) is passed through, the second nut(42, 43 or 44) can be fastened to the protruded end after fastening to the female threaded hole(80b) of the first member(80) so as to pass through the female threaded hole(80b). [55] In case the second nut(42, 43 or 44) is fastened in the opposite direction to the first nut(41), although the first nut(41) is about to rotate a little in the release direction by vibration, etc., after being fastened and the rotation of the first nut(41) in the release direction is about to rotate the second nut(42, 43 or 44) by friction, etc., the rotation of the first nut(41) in the release direction causes the rotation of the second nut(42, 43 or 44) in the fastening direction and therefore the second nut(42, 43 or 44) is further fastened as in Figs. 4 to 8, thereby looseness of the first nut(41) being perfectly prevented. [56] Although the embodiment in which the parent member(50) and the parent member(50) are fastened with the connecting plate members(51,52) is shown and explained above, an embodiment for fastening the parent member(50) and the parent member(50) in an overlap configuration without the connecting plate members(51,52) can be realized similarly. Further, the bolt can be fastened directly to a female threaded hole(80a or 80b) without the first nut(41) as in Fig. 13 or Fig. 14, so that the parent member(80) and the parent member(80) of machine apparatus, structures, etc., can be fastened and fixed. [57] Fig. 19 illustrates a schematical sectional view of another example of a fastened structure of a bolt(160) according to further another embodiment of the present invention. In Fig. 19, the nut is a double purpose nut(70) both for fastening and for looseness prevention, said nut having both threads formed for mating engagement with the right-handed thread(61) and the left-handed thread(62) of the bolt(160) in an overlap configuration in the same internal diameter as in Fig. 9. In this case, the bolt(160) passes through each bolt hole of the parent member(50) and the connecting plate members(51,52), etc., and then, the double purpose nut(70) is fastened to the thread portion of the bolt(160) protruded opposite to a bolt head. In case of being fastened to the right-handed thread(61), the double purpose nut(70) is fastened to the right-handed thread(61) in the fastening direction of the right-handed thread(61) to a position in which the double purpose nut(70) can be also fastened to the left-handed thread(62) by the reverse direction rotation(including the fastening position with adding pressure). At this time, it is preferable to fasten the double purpose nut(70) in the reverse direction with adding a force, so that the fastening force is further increased. Since a fastening force is further increased although the double purpose nut(70) is rotated in any direction by vibration, etc., the fastening is realized by only the double purpose nut(70) and looseness of the double purpose nut is perfectly prevented. [58] The above-mentioned bolt(l 10, 120, 130 or 160), the first nut(41) for fastening, the second nut(42, 43 or 44) for looseness prevention, the double purpose nut(70) for fastening and for looseness prevention can be easily changed within the design range according to various thread kinds of bolts and nuts, such as a stud bolt, a round head screw, the thread line number, the thread ridge shapes, the thread parallel or its inclined degree, etc., except the above-mentioned constructions. In case of including a washer and even in case the non-thread portion length is formed a little longer than the total width(W,Wb) of the unfastened members, the first nut(41) and the second nut(42, 43 or 44) can be fastened, and the general technique about threads can be adapted or changed within the scope of the present invention besides the above-mentioned technical principles of the present invention. [59] In order to prevent unstable contact in contact surfaces of the first nut(41) and the second nut(42, 43 or 44) which can occur due to machine error, and ensure exact fastening, various washers can be inserted in the middle, and prominences and de¬ pressions can be formed on the contact surfaces as in Figs. 20 and 21. The prominences and depressions in Fig. 21 are formed circumferentially and are shown as lines radially. Thus, the inner radially the narrower width becomes. The prominences and depressions are preferably formed so as to be mated with each other in fastening the first nut(41) and the second nut(42, 43 or 44) without being limited to the foregoing example. Industrial Applicability [60] The present invention, as a bolt structure, or a bolt and nut assembly structure, can be utilized instead of fastening by the conventional bolts or bolts and nuts in various machine apparatus, various structures, various constructions, etc., because unification can be achieved by being capable of being fastened regardless of directions of their screw threads, looseness can be completely prevented due to stronger strength for looseness-prevention, and also process or manufacture and fastening assembly can become easier even with simple construction.