Patent Publication Number: US-7220091-B2

Title: Fastening nuts with loosening assist functions

Description:
This application claims priority to Japanese patent application serial number 2004-133709, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to fastening nuts, such as nuts for fastening grinding wheels to the spindles of portable grinders. In particular, the present invention relates to fastening nuts with loosening assist functions for facilitating the loosening of the nuts via application to the nuts of small loosening forces. 
     2. Description of the Related Art 
     In general, a fastening nut is engaged with and fastened onto a male thread formed on a front end of a spindle in order to mount a disk-like grinding wheel to a motor-driven spindle of a portable grinder. The grinding wheel is mounted so as to not move in an axial direction or also in a rotational direction relative to the spindle. The grinding wheel can be clamped between the nut and a flange formed on the spindle so as to not move in an axial direction or in a rotational direction. 
     In this kind of grinder, the resistance force applied to the grinding wheel by a workpiece during a grinding operation may act to further fasten (i.e., tighten) the nut. Therefore, it is often difficult to loosen the nut in order to remove the grinding wheel from the spindle. In order to solve this problem, various measures have been proposed in the art. 
     For example, U.S. Pat. No. 5,175,963 (corresponding to Japanese Patent No. 2801324) teaches a fastening nut in which steel balls are provided. The steel balls maintain a state where wedge members, disposed at tri-sectional positions about a male threaded portion of a spindle, are fitted between a grinding wheel and a nut body fastened onto the male treaded portion. The steel balls can maintain the fastened condition of the nut body onto the male threaded portion. According to this type of fastening nut, rotation of an operation ring containing recesses, formed in the inner circumference of the operation ring for receiving the steel balls, allows the steel balls to move into the recesses and become displaced radially outward. Consequently, the wedge members are moved in directions for facilitating removal from positions between the nut body and the grinding wheel. Therefore, this operation enables a relatively small operational force to loosen the nut body, which has been fastened onto the male threaded portion of the spindle. 
     Japanese Laid-Open Utility Model publication No. 4-118972 teaches a fastening nut in which steel balls are respectively disposed between an operation ring and nut segments that correspond to tri-sectional segments of a nut about a male threaded portion of a spindle. The steel balls can be moved into recesses formed in the nut segments so as to displace the nut segments in radially outward directions. The nut segments fastened onto the male threaded portion of the spindle can then be loosened. 
     Throughout the specification, the term “radial direction” in relation to the movement of the nut segments is used to indicate the radial direction about an axis of a male threaded portion (or female threaded portion) to which a nut is fastened. Therefore, the term “radially outward direction” is used to indicate a direction away from the axis of the male threaded portion. The term “radially outward direction” is used to indicate a direction towards the axis of the male treaded portion. 
     However, in the case of the former type of fastening nut incorporating separated wedge portions, a single steel ball is engaged with and released from each of the corresponding wedge portions. Similarly, in the case of the latter type of fastening nut incorporating nut segments, a single steel ball is engaged with and released from each of the corresponding nut segments. Therefore, there exists a problem in that the positions of the wedge portions or the nut segments are liable to become unstable, particularly when the nut is fastened. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the present invention to teach improved fastening nuts that can be easily loosened, for example, in order to remove a grinding wheel from a grinder. Additionally, an object of the present invention is to teach improved fastening nuts that can exert a stable fastening force when the nuts used for fastening. 
     In one aspect of the preset teachings, fastening nuts are taught that include an operation member, a female threaded member, and a control device. The operation member is operable by an operator so as to rotate in a fastening direction and a loosening direction. The control device is coupled between the operation member and the female threaded member. The control device includes a plurality of movable members, such as nut segments and wedge members for example, and a plurality of control members, such as rollers and balls for example. The movable members are arranged in the circumferential diction about the axis of the nut. Each movable member is movable at least between a first position and a second position along a radial direction from the axis of the nut. The first position enables the fastening of the female threaded member onto the male treaded member. The second position enables the loosening of the female threaded member. The control members are interposed between the operation member and each of the corresponding movable members. The control members prevent the movement of the movable members from a fist position to the second position when the operation member rotates in a fastening direction. On the contrary, the control members permit the movement of the movable members from the first position to a second position when the operation member rotates in a loosening direction. 
     Therefore, each movable member may reliably be held in a first position by the plurality of the control members. As a result, the fastening nut can be reliably fastened onto the male threaded member via a relatively strong force. 
     In another aspect of the present teachings, fastening nuts are taught that include a base, a cover, a plurality of nut segments, and a corresponding plurality of control members. The base has a first insertion hole for receiving the male threaded member. The cover has a second insertion hole for receiving the male treaded member and also includes a circumferential wall. Together the nut segments comprise a virtual single nut. The nut segments are arranged at regular intervals in a circumferential direction about the central axis of the virtual single nut. The nut segments are disposed between the base and the cove and are movable in a radial direction about the axis of the nut. The control members are disposed between each nut segment and the circumferential wall of the cover in order to prevent each nut segment from moving in a radially outward direction with respect to the nut axis. Relief recesses are formed in the circumferential wall of the cover and/or in each nut segment. The relief recesses are engageable with the corresponding control members to permit each nut segment to move in the radially outward direction when the cover has rotated in a nut loosening direction relative to the base. A loosening assist function is therefore affected to reduce the fastening force applied by each nut segment onto the male dreaded member. 
     With this configuration, the radially outward movement of each nut segment is prevented by the plurality of control members. Therefore, the position of each nut segment in the radial direction with respect to the nut axis can be more reliably maintained in comparison with the shown fastening nut, in which the radial movement of each nut segment is restricted by a single control member (i.e., a single steel ball) in order to provide a loosening assist function. Therefore, the fastening nut of the current invention can be reliably fastened onto the male threaded member via a relatively strong force. 
     In one embodiment, the fastening nuts further include an auxiliary member disposed at least between two adjacent control members for each nut segment. The auxiliary member functions in part to keep a minimum distance between the control members. With this arrangement, it is possible to clearly distinguish the engaging condition of the control members with the relief recesses and the disengaging condition of the control members from the relief recesses. 
     In another embodiment, the fastening nuts further include at least one spring that normally biases the cover in a nut fastening direction relative to the base. Therefore, when the cover is rotated in the nut fastening direction in order to perform a fastening operation, the cover and the base may rotate together in the nut fastening direction. On the contrary, when the cover is rotated in the nut loosening direction in order to perform a loosening operation, the movement of the cover precedes the movement of the base in the nut loosening direction. After the control members engage the relief recesses, the nut segments can then move in the radially outward direction to enable the loosening of the fastening nut from the male treaded member via a relatively small force. 
     In a further embodiment each of the control member is configured as a cylindrical roller that has a longitudinal axis extending substantially parallel to the nut axis. With this arrangement, it is possible to mare stably restrain the radially outward movement of tire nut segments in comparison with using known control members configured as balls. 
     In a still further embodiment, the fastening nuts further include a stopper device that permits iron of the male threaded member of the spindle from tike base side of the fastening nut and prevents the insertion of the male threaded member from the cover side of the fastening nut. Therefore, the fastening nuts can be reliably fastened onto the male threaded member without permitting improper insertion from the cover side of the fastening nut. As a result, the loosening assist function can be readably implemented. 
     In a still further embodiment, the fastening nuts further includes a seal device interposed between adjacent nut segments positioned in a circumferential direction. Therefore, foreign particles may not be allowed to enter into the space between the nut segments and the circumferential wall of the cover. As a result, the smooth movement of the control members can be ensured, enabling the performance of the given function of the fastening nuts. 
     Preferably, the seal device includes a seal member with a pair of ring portions, and a plurality of connecting portions connecting between the ring portions. The ring portions and the connecting portions may be formed integrally with each other. One of the ring portions is clamped between the base and the various nut segments. The other of the ring portions is clamped between the cover and the nut segments. Each of the connecting portions is clamped between two adjacent nut segments in the circumferential direction. With this configuration, in addition to providing a seal between the nut segments, it is possible to provide a seal between the base and the nut segments and a seal between the cover and the nut segments. In addition, the handling and the assembling of the seal member to the fastening nut can be facilitated. 
     In a further aspect of the present teachings, fattening nuts are taught that include a nut body, a pressing flange, a plurality of wedge members, an operation member, and a plurality of control members, The nut body includes a female portion and a flange portion. The flange portion extends radially outward from one axial end of the female threaded portion. The pressing flange is disposed so as to oppose the flange portion of the nut body. The pressing flange is movable in an axial direction relative to the nut body. The wedge members are arranged at regular intervals in a circumferential about the nut axis. Each wedge member is interposed between the pressing flange and the flange portion of the nut body in order to affect a wedging function. The operation member has a circumferential wall that is disposed on the outer peripheral side of the wedge members and encloses the flange portion of the nut body and the pressing flange. The control members are interposed between the operation member and each wedge member in order to prevent each wedge member from moving in the radially outward direction. A plurality of relief recesses are formed in either the circumference wall of the operation member or in each wedge member. The relief recesses are respectively engageable with the control members corresponding to each wedge member. The control members for each wedge under are disengaged from the relief recesses in order to position each wedge member in a radially inward position for implementing the wedge function when the operation member is in a fist position on the side of a nut fastening direction. On the contrary, the control members for each wedge member are engaged with the relief recesses in order to permit each wedge member to move radially outward from the radially inward position for releasing the wedge function when the operation member is rotated from the first position in a nut loosening direction, which is opposite to the nut fastening direction. 
     With this arrangement, in order to instill the fastening nut onto the male threaded member, the male threaded member may be inserted into and engaged with the female threaded portion from the side of the pressing flange of the fastening nut. The operation member may then be rotated in the fastening direction. As long as the operation member is rotated in the fastening the control members are positioned so as to not engage with the relief recesses, restraining the movement of the wedge members in the radially outward direction. The pressing flange is held in a position away from the flange portion of the nut body. Therefore, the fastened condition of the fastening nut may be locked as the operation member is further rotated in the nut fastening direction after the pressing flange has contacted with the fastened object. On the contrary, in the event that the operation member is rotated in the loosening direction, the control members may be brought so as to engage the relief recesses, enabling the movement of the wedge members in the radially outward direction. The pressing flange can move axially toward the flange portion of the nut body, releasing the fastened condition of the fastening nut. 
     In particular, the radially outward movement of each wedge member is prevented by the plurality of control members. Therefore, the position of each wedge member in the radial direction with respect to the nut axis can be reliably maintained in corrosion with the known fastening nut in which a corresponding single control member (i.e., a steel ball) restricts the radial movement of each wedge member. Consequently, the fastening nut of the current invention can be reliably fastened onto the male threaded member with a strong force. 
     In one embodiment, the fastening nut further includes an auxiliary member disposed at least between two adjacent control members for each wedge member. The auxiliary member functions to keep a minimum distance between the two control members. In another embodiment, each of the control members may be configured as a cylindrical roller with a longitudinal axis extending substantially parallel to the nut axis. 
     In a further embodiment, the fastening nut further includes at least one spring that normally biases the operation members in the nut fastening direction relative to the flange. 
     In a further aspect of the present teachings, rotary tools are taught that include the fastening nut of the various aspects listed above. Therefore, the fastening nut can be easily loosened even if the nut has been excessively fastened (e.g., over tightened) onto the male threaded member of a spindle due to the resistance a workpiece applies to a rotary device, such as a grinding wheel, during the use of the rotary tool. As a result, the operation for replacing a worn rotary blade with another rotary blade can be easily performed. 
     In one embodiment, a fastening nut for fastening onto a male threaded member may include a nut body. The nut body may include a female threaded portion defining a nut axis and comprising a first axial end and a second axial end and a flange portion extending radially outward from the first axial end. A pressing flange may be slidingly disposed around a section of the female threaded portion proximate to the second axial end and the pressing flange may oppose at least a section of the flange portion in an axial direction and is slidingly movable relative to the nut body in the axial direction. A plurality of wedge members may be at regular intervals along a circumferential direction about the nut axis and each of the plurality of wedge members is interposed between the pressing flange and the flange portion and an operation member having a circumferential wall may be disposed on an outer circumferential side of the plurality of wedge members and enclosing the flange portion and the pressing flange. The fastening nut may include two control members for each corresponding wedge member of the plurality of wedge members, wherein each of the two control members are interposed between the operation member and the corresponding of wedge member and each of the two control members define a first wedge position for each corresponding wedge member when the operation member is in a first operation position. The fastening nut may include two relief recesses corresponding to each of the two control members and formed in the circumferential wall of the operation member or in each of the corresponding wedge members. Each of the two control members may define a second wedge position for each corresponding wedge member when the operation member is in a second operation position. The second wedge position may be radially outward of the first wedge position to an extent that each of the two control members are engaged with the corresponding two recesses. The first wedge position may fix the pressing flange at a first axial distance from the flange portion. The second wedge position may allow the pressing flange to move to a second axial distance from the flange portion. The first axial distance may be greater than the second axial distance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial schematic view showing the attachment of a grinding wheel to the spindle of a grinder via a fastening nut according to a first representative embodiment of the current invention; and 
         FIG. 2  is an enlarged cross-sectional view taken from the direction indicated by the arrows II—II in  FIG. 1 , showing the internal structure of the fastening nut; and 
         FIG. 3  is a cross-sectional view taken along line III—III in  FIG. 2 , showing a vertical sectional view of the fastening nut in the fastening-lock position; and 
         FIG. 4  is a cross-sectional view taken along line IV—IV in  FIG. 2 , showing another vertical sectional view of the fastening nut; and 
         FIG. 5  is a cross-sectional view taken along line V—V in  FIG. 2 , showing another vertical sectional view of the fastening nut; and 
         FIG. 6  is a plan view showing the internal structure of the fastening nut in the fastening-unlock position; and 
         FIG. 7  is a plan view of a base of the fastening nut; and 
         FIG. 8  is a cross sectional view taken along line VIII—VIII in  FIG. 7 , showing a vertical sectional view of the base; and 
         FIG. 9  is a plan view of a cover of the fastening nut, showing the inner side of the cover; and 
         FIG. 10  is a cross sectional view taken along line X—X in  FIG. 9 , showing a vertical sectional view of the cover; and 
         FIG. 11  is a plan view showing the positional relationship of the nut segments of the fastening nut where one of the nut segments is indicated by solid lines and the other two of the nut segments are indicated by chain lines; and 
         FIG. 12  is an individual view of a stopper of the fastening nut from a direction perpendicular to the nut axis; and 
         FIG. 13  is a view of the stopper as viewed in the direction of arrow XIII in  FIG. 12  along the nut axis, showing a plan view of the stopper; and 
         FIG. 14  is a view of the stopper as viewed in the direction of arrow XIV in  FIG. 12 , perpendicular to the nut axis and perpendicular to  FIG. 12 , showing a side view of the stopper; and 
         FIG. 15  is a vertical sectional view of the fastening nut and illustrating the operation of the stopper when a male threaded portion is inserted into the female threaded portion of the fastening nut from the side of the cover; and 
         FIG. 16  is a plan view of the internal structure of a fastening nut according to a second representative embodiment, showing the state where an operation member is turned to a fastening side; and 
         FIG. 17  is a plan view similar to  FIG. 16  but showing the operation where the operation member is rotated toward a loosening side against the biasing forces of the comparison coil springs; and 
         FIGS. 18–20  are vertical sectional views respectively taken along lines XVIII—XVIII, XIX—XIX and XX—XX in  FIG. 16  and indicating an inserting direction of the male threaded portion by an outline arrow; and 
         FIG. 21  is a vertical sectional view taken along line XXI—XXI in  FIG. 17  and indicating the inserting direction of the male threaded portion by the outline arrow; 
         FIGS. 22 and 23  are plan views of the internal structure of a fastening nut according to the second representative embodiment, showing relief recesses in the operations member; and 
         FIGS. 24 and 25  are plan views of the internal structure of a fastening nut according to the first representative embodiment, showing relief recesses in the cover. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide improved fastening nuts and methods of manufacturing such fastening nuts. Representative examples of the present invention, which examples utilize many of these additional feature and teachings both separately and in conjunction with one another, will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Moreover, various features of the representative examples and the dependent claims may be combined in ways that are not specifically enumerated in order to provide additional useful embodiments of the present teachings. 
     First Representative Embodiment 
     A first representative embodiment of the present invention will now be described with reference to  FIGS. 1 to 15 . Referring to  FIG. 1 , a grinding wheel  2  is mounted to a portion of a grinder  1  by utilizing a representative fastening nut  10 . The grinder  1  is for example a rotary tool and the grinding wheel  2  is for example a rotary blade. The construction of the grinder  1  itself is known in the art and will not be described in detail. Thus, the grinder  1  may have a tool body (not shown) and a spindle  3  extending from the tool body. The spindle  3  is rotatably driven by an electric motor (not shown) disposed within the tool body.  FIG. 1  shows only the spindle  3  portion of the grinder  1 . 
     A flange  3   a  and a male threaded portion  3   b  are formed on the front end of the spindle  3 . In this representative embodiment, the male threaded portion  3   b  is configured as a right-hand thread. Therefore, when the fastening nut  10  is engaged with the male threaded portion  3   b , rotating the fastening nut  10  in a right hand direction (i.e., clock-wise) may securely fastened the fastening nut  10  onto the male threaded portion  3   b . On the contrary, by rotating the fastening nut  10  in a left-hand direction (i.e., counter clock-wise), the fastening nut  10  may be loosened from a fastened condition with the male threaded portion  3   b.    
     The grinding wheel  2  is mounted to the front end of the spindle  3  so as to not move relative to the spindle  3  in both the axial diction and the rotational direction. More specifically, the grinding wheel  2  is fitted onto the male threaded portion  3   b  such that the male threaded portion  3   b  is inserted through a central mounting hole  2   a  farmed in the grinding wheel  2 , until one side of the grinding wheel  2  contacts the flange portion  3   a . In this configuration, the fastening nut  10  is engaged with and fastened onto the male threaded portion  3   b . The grinding wheel  2  may be removed from the spindle  3  by loosening the fastening nut  10  from the male threaded portion  3   b . As will be explained later, the representative fastening nut  10  has a function to enable an operator to easily loosen the fastening nut  10  via the exertion of a relatively small force (hereinafter called “loosening assist function”), even if the fastening nut  10  has been excessively fastened. The fastening nut  10  may be excessively tightened as a result of the application of an external force to the fastening nut  10  in a fastening direction due to the resistance applied to the grinding wheel  2  by a workpiece during a grinding operation. 
     The detailed construction of the fasting nut  10  is shown in  FIGS. 2 to 5 . The fastening nut  10  includes a disk-like base  11  and a cup-shaped cover  12 . In addition, the fastening nut  10  also includes three nut segments  13 , three pairs of restriction rollers  14 , and three auxiliary rollers  15 , assembled between the disk-like base  11  and the cup-shaped cover  12 . One pair of the restriction rollers  14  and one of the au rollers  15  are assigned to each one of the nut segments  13 . In this specification, the restriction rollers  14  may be referred to as restriction members and the auxiliary rollers  15  may be referred to as auxiliary members. 
     The base  11  is individually shown in  FIGS. 7 and 8 . An insertion hole  11   a  is formed centrally of the base  11  in order to permit insertion of the male headed portion  3   b  of the spindle  3 . The fastening nut  10  is engaged to the male threaded portion  3   b  with the fastening nut  10  oriented such that the male treaded portion  3   b  is inserted firm the side of the insertion hole  11   a  of the base  11 . 
     An engaging recess  11   b  having a small depth is formed in the inner wall (i.e., the wall on the viewing side of  FIG. 7  or on the upper side as viewed in  FIG. 8 ) of the base  11  around the insertion hole  11   a . Three retaining recesses  11   c , having the same depth as the engaging recess  11   b , are formed in series with the engaging recess  11   b . The retaining recesses  11   c  extend radially outward from the engaging recesses  11   b  at tri-sectional positions along the circumferential direction. In addition, three guide recesses  11   d  are formed in the inner wall of the base  11 , also at tri-sectional positions along the circumferential direction. Each of the guide recesses  11   d  is elongated so as to have a predetermined length along an arc about the center of the base  11 . The guide recesses  11   d  have a slight depth similar to the engaging recess  11   b  and the retaining recesses  11   c.    
     The cover  12  is individually shown in  FIGS. 9 and 10 . The cover  12  has a cup-shaped configuration and has an outer diameter that is substantially the same as the outer diameter of the base  11 . An insertion hole  12   a , having substantially the same diameter as the insertion hole  11   a  of the base  11 , is formed in the center of the cover  12 . Tree engaging projections  12   c  are formed on the inner peripheral surface of a circumferential wall  12   b  of the cover  12  and extend radially inwardly towards the center of the cover  12 . Also, the engaging projections  12   c  are positioned at tri-sectional positions along the circumferential direction. An engaging recess  12   d , having a slight depth, is formed in the cover about the insertion hole  11   a  so as to correspond to the engaging recess  11   b  of the base  11 . 
     The three nut segments  13  are assembled within the cover  12  and are individually represented in  FIG. 11 . The nut segments  13  correspond to sections of a single complete nut divided at equally spaced tri-sectional positions along the circumferential direction. Therefore, the nut segments  13  all have the same general configuration. The nut segments  13  are arranged in tri-sectional positions along the circumferential direction of the cover  12  to virtually form a single female thread S that is threadably engageable with the male treaded potion  3   b . The nut segments  13  are positioned so as to oppose the engaging recess  11   b  of the base  11  and to oppose the engaging recess  12   d  of the cover  12 . The engaging recess  11   b  and the engaging recess  12   d  permit the nut segments  13  to move a little distance in the radial direction with respect to the center of the female thread S. 
     Each of the nut segments  13  has a threaded hole part  13   a  at a position corresponding to the inner circumferential side of the female thread S. Each nut segment  13  also includes two relief recesses  13   b  at a position corresponding to the outer circumferential side of the female thread S. Further, each of the relief recesses  13   b  has a sectional configuration corresponding to an arc having a radius, for example such as a radius of about 1.0 mm, in order to enable the engagement of a part of the corresponding restriction roller  14 . In addition, an engaging projection  13   c  is formed on the outer peripheral surface in a position adjacent to one end, in the circumferential direction, of each nut segment  13 . Each engaging projection  13   c  extends radially outward from the outer peripheral surface so that the engaging projection  13   c  extends radially outward from the engaging recesses  11   b  into the retaining recess  11   c  of the base  11  and the engaging recess  12   d  of the cover  12  in the assembled state. In this way, the threaded hole parts  13   a  of the three nut segments  13  together form the virtual single female thread S. The size and the configuration of the nut segments  13  are determined such that the threaded hole parts  13   a  are always position on the radially inner side of the insertion hole  11   a  of the base  11  and the insertion hole  12   a  of the cover  12 , over the entire movable range of the nut segments  13  in the radial direction. 
     As shown in  FIG. 2 , one pair of restriction rollers  14  and one associated auxiliary roller  15  are disposed between the outer circumference of each nut segment  13  and the circumferential wall  12   b  of the cover  12 . More specifically, the one pair of the restriction rollers  14  and the one auxiliary roller  15  are positioned between one of the engaging projections  12   c  and the engaging projection  13   c  of each nut segment. In this representative embodiment, each of the restriction rollers  14  has a cylindrical configuration and has a diameter of 5 mm, for example. Each of the auxiliary rollers  15  also has a cylindrical configuration and has a diameter of 4.5 mm. The diameters am not limited to any specific size, such as 4.5 mm but may be any different size appropriate for the application, such as 4.0 mm. 
     One end of each auxiliary roller  15  is fitted into one of the guide recesses  11   d  of the base  11 . Therefore, each auxiliary roller  15  is retained such that each auxiliary roller  15  can move along the outer peripheral portion of the corresponding nut segment  13  within a movable range limited by the guide recess  11   d.    
     Compression coil springs  16  are disposed at tri-sectional positions in the circumferential direction, where no restriction rollers  14  and no auxiliary roller  15  are positioned. Each compression coil spring  16  is interposed between one of the engaging projections  12   c  of the cover  12  and an engaging projection  13   c  of one of the nut segments  13 . Therefore, the cover  12  is biased in a clockwise direction as viewed in  FIG. 2  (i.e., the fastening direction of the fastening nut  10 ). Consequently, a pair of the restriction rollers  14  and a single auxiliary roller  15 , positioned between each engaging projection  12   c  of the cover  12  and the engaging projection  13   c  of each nut segment  13 , are forced to be clamped therebetween. For the purposes of explanation, a circumferential space defined between each engaging projection  12   c  of the cover  12  and the engaging projection  13   c  of each nut segment  13 , used for positioning the pair of restriction rollers  14  and an auxiliary roller  15 , will be hereinafter called “roller accommodating region R.” In addition, a circumferential space defined between one of the engaging projections  12   c  of the cover  12  and the engaging projection  13   c  of one of the nut segments  13 , used for positioning the compression coil spring  16 , will be herein after called “spring accommodating region B.” 
     In the state shown in  FIG. 2 , due to the biasing forces of the compression coil springs  16 , the cover  12  is positioned at the most right-hand position relative to the base  11 . Each roller accommodating region R has the shortest possible length in the circumferential direction and each spring accommodating region B has the longest possible length in the circumferential direction. Therefore, the pair of the restriction rollers  14  and the auxiliary roller  15  are clamped between each engaging projection  12   c  of the cover  12  and the engaging projection  13   c  of each nut segment  13 , and are prevented from moving in a circumferential direction. In addition, in this configuration the pair of the restriction rollers  14  does not engage with the relief recesses  13   b  of a corresponding nut segment  13 . Therefore, the pair of the restriction rollers  14  is clamped between the circumferential  12   b  of the cover  12  and the outer peripheral surface (other than the relief recess  13   b  portions) of the corresponding nut segment  13 . As a result, the nut segments  13  are forced in a direction so as to reduce the overall diameter of the female threaded portion S. This results in the condition that the nut segments  13  are prevented from moving in the radially outward direction. This configuration will hereinafter be called the “fastening-lock condition” of the fastening nut  10 . 
     In the fastening-lock condition, the fastening nut  10  may be engaged with and fastened onto the male threaded portion  3   b . The fastening nut  10  can be rotated relative to the male threaded portion  3   b  while the pair of the restriction rollers  14  and the auxiliary roller  15  are clamped between each engaging projection  12   c  of the cover  12  and the engaging projection  13   c  of each nut segment  13 , so as to be integrated with the cover  12  and the corresponding nut segment  13 . 
     Conversely, when the cover  12  has been rotated in a counterclockwise direction (the loosening direction of the fastening nut  10 ) as indicated by an arrow B in  FIG. 6 , each of the engaging projection  12   c  moves relative to the related engaging projection  13   c . Each resulting roller accommodating region R may have the longest possible length in the circumferential direction and each spring accommodating region B may have the shortest possible length in the circumferential direction. In this configuration, the pair of the rest on rollers  14  and the auxiliary roller  15  in each roller accommodating region R can move in the circumferential direction. The pair of the restriction rollers  14  in each roller accommodating region R may then respectively engage with the relief recesses  13   b . Therefore, each of the nut segments  13  may be permitted to move radially outward by a slight distance (approximately 0.1 mm in this representative embodiment). As a result, the fastened state of the nut segment  13  with the male threaded portion  3   b  may be loosened or released. This condition will hereinafter be called the “fastening-unlock” condition. 
     As described above, in the fastening-lock condition shown in  FIG. 2 , the compression coil springs  16  force the cover  12  to be positioned at the right-most position relative to the base  11 , this may rest in the roller accommodating regions R having the shortest length in the circumferential direction, restraining the radially outward movement of the nut segments  13 . Therefore, the fastening nut  10  may be locked in the fastened condition with the male threaded portion  3   b  of the spindle  3 . Conversely, when the cover  12  is rotated in the left-hand direction against the biasing forces of the compression coil springs  16 , the result may be the fastening-unlock condition shown in  FIG. 6 . In this condition, the roller accommodating regions R may have the longest length in the circumferential direction in order to permit the radially outward movement of the nut segments  13 . Therefore, the fastening condition of the fastening nut  10  with the male threaded portion  3   b  of the spindle  3  may be released. As a result, it is possible to rotate the fastening nut  10  relative to the male threaded portion  3   b  of the spindle  3  in the loosening direction via a relatively small force. 
     As shown in  FIGS. 2 and 6 , a seal member  17  made of rubber for example, is inserted into the gap formed between each of two circumferentially adjacent nut segments  13 . Thus, three seal members  17  are provided in this representative embodiment. The position of each seal member  17  is chosen so as to not interact with or restrict the movement of the nut segments  13  in the radial direction. Since the seal members  17  block the circumferential gaps between the nut segments  13 , foreign particles may not enter from the female threaded portion S into the spring accommodating regions B or into the roller accommodating regions R. Therefore, situations can be avoided involving foreign particles causing potential malfunction of the fastening nut  10 . 
     As shown in  FIGS. 3 to 5 , three seal rings  17  are integrally joined to each other at their respective upper portions and lower portions via annular seal rings  18 . One of the seal rings  18  is clamped between the nut segments  13  and the base  11 . The other of the seal rings  18  is clamped between the nut segments  13  and the cover  12 . Therefore, the seal rings  18  may respectively provide a seal between the nut segments  13  and the base  11  and a seal between the nut segments  13  and the cover  12 . 
     A stopper is inserted into the circumferential gap between two of the nut segments  13  in order to inhibit the insertion of the male threaded portion  3   b  into the fastening nut  10  in an inappropriate direction. If the representative fastening nut  10 , including the loosening assist function as described above, were engaged and fastened onto the male thread  3   b  by initially inserting the male threaded portion  3   b  into the insertion hole  12   a  of the cover  12 , and not by initially inserting the male threaded portion  3   b  into the insertion hole  11   a  of the base  11 , the cover  12  may be rotated relative to the base  11  in a direction so as to increase the circumferential length of the roller accommodating regions R (and subsequently actuating the loosening assist function) during the fastening operation. Conversely, during an attempted loosening operation, the cover  12  may be rotated in a direction so as to reduce the circumferential length of the roller accommodating regions R (resulting in the fastening-lock condition). These rotating directions are opposite to the rotating directions necessary for correctly implementing the loosening assist function as described above. As a result, the loosening assist function may not be at all effective if the fastening nut  10  is assembled improperly. For this reason, a stopper  20  is provided in order to inhibit such improper fastening operation due to the installation of the fastening nut  10  in an upside down orientation as compared to the orientation required for the normal fastening operation. 
     The stopper  20  is exclusively shown in  FIG. 12  and is formed by a steel wire that has been bent so as to enable resilient deformation. The stopper  20  has an engaging portion  20   b  adapted to extend radially inwardly beyond the inn diameter of the nut segments  13  (i.e., inside of the face threaded portion S). The stopper  20  also has two legs  20   a  respectively extending in the right and left directions from the lower end of the engaging portion  20   b , as viewed in  FIG. 12 . As shown in  FIGS. 2 to 5 , one of the legs  20   a  is clamped between one of two adjacent nut segments  13  and the base  11 . The other of the legs  20   a  is clamped between the other of two adjacent nut segments  13  and the base  11 . With the legs  20   a  thus clamped, one end of the engaging portion  20   b  on the side opposite to the legs  20   a  extends into the space within the female threaded portion S. 
     As shown in  FIG. 13 , the legs  20   a  are slightly curved to have an arc-shaped configuration in plan view. Therefore, when the legs  20   a  are clamped between the nut segments  13  and the base  11 , the stopper  20  may be inhibited or prevented from rotating about either of the legs  20   a . In addition, the engaging portion  20   b  may be positioned and held such that the protruding distance of the engaging portion  20   b , into the space within the female threaded portion S, gradually increases in a direction form the side of the insertion hole  11   a  of the base  11  towards the side of the insertion hole  12   a  of the cover  12 . Thus, the engaging portion  20   b  may be held to be inclined upward toward the space within the female threaded portion S, as shown in  FIG. 15 . Further, the engaging portion  20   b  can be resiliently held in the inclined position (hereinafter also called a “restricting position”), since the curved legs  20   a  are clamped between the nut segments  13  and the base  11 . 
     As the male threaded portion  3   b  is inserted into the female threaded portion S, the male threaded portion  3   b  may press the engaging portion  20   b  of the stopper  20  so as to pivot the engaging portion  20   b  from a restricting position, where the stopper  20  extends into the female threaded portion S as indicated by the solid lines in  FIG. 15 , towards an upright position, against the biasing force of the engaging portion  20   b . As a result, the engaging portion  20   b  may be turned aside to a withdrawal position where the engaging portion  20   b  does not extend into the female treaded portion S as indicated by chain lines in  FIG. 15 . In other words, the engaging member  20   b  may be entirely withdrawn into the gap between the two segment nuts  13  so as to not substantially interfere with the continued insertion of the threaded portion  3   b.    
     In proper operation, the male threaded portion  3   b  of the spindle  3  is inserted from the side of the insertion hole  11   a  of the base  11  (i.e., the lower side as viewed in  FIG. 1 ). Then, the fastening nut  10  is engaged with and fastened onto the male threaded portion  3   b  by rotating the fastening nut  10  in the fastening direction. During the process of fastening the fasting nut  10  by inserting the male threaded portion  3   b  from the side of the insertion hole  11   a , the front end of the male threaded pardon  3   b  may press the engaging portion  20   b  of the stopper  20 , applying a force against the resilient force of the stopper  20 . As a result, the engaging portion  20   a  may be gradually pivoted from a restricting position, indicated by solid lines in  FIG. 15 , to the withdrawn position indicated by chain lines in  FIG. 15 . Therefore, in the case of proper operation, the stopper  20  does not serve to inhibit the insertion of the male threaded portion  3   b  into the female threaded portion S. 
     Alternatively, in the event that the male threaded portion  3   b  is oriented so as to be inserted into the finale treaded portion S from the side of the insertion hole  12   a  of the cover  12 , as indicated by an outline arrow in  FIG. 15 , the front end of the male threaded portion  3   b  may come in contact with one end of the engaging portion  20   b  of the stopper  20  and may subsequently be prevented from moving any further. Therefore, in this case, the stopper  20  may serve to inhibit the insertion of the male threaded portion  3   b  into the female threaded portion S in a direction opposite to the proper direction. 
     In this way, as long as the fastening nut  10  is engaged with and fastened onto the male threaded portion  3   b  of the spindle  3  while the male threaded portion  3   b  is oriented such that that the male threaded portion  3   b  is first inserted into the insertion hole  11   a  of the base  11 , the engaging portion  20   b  of the stopper  20  is pressed by the male threaded portion  3   b  so as to be withdrawn from inside of the female threaded portion S. Therefore, the iron of the male threaded portion  3   b  into the female threaded portion S and the subsequent fastening operation of the fastening nut  10  may be performed without interference. Conversely, in the event that the male threaded portion  3   b  is moved such that the male threaded portion  3   b  is first inserted into the insertion hole  12   a  of the cover  12 , the engaging portion  20   b  of the stopper  20  is pressed by the male threaded portion  3   b  so as to slightly extend further inside of the female threaded portion S. Consequently, further insertion of the male threaded portion  3   b  into the female threaded portion S may be inhibited. The result is that the fastening nut  10  may be prevented from being improperly fastened onto the male threaded portion  3   b.    
     As described above, the fastening nut  10  may be completely fastened onto the male threaded portion  3   b  of the spindle  3  only if the male threaded portion  3   b  has been inserted from the side of the insertion hole  11   a  of the base  11 . An improper inserting operation of the male threaded portion  3   b  in a direction opposite to the proper don can be reliably inhibited. Therefore, the rotation of the cover  12  in the fastening-unlock direction relative to the base  11  reliably implements the loosening assist function. The loosening assist friction enables the radially outward displacement of the nut segments  13 . This releasing the condition where the nut segments  13  are pressed against the male threaded portion  3   b  in the radially inward direction toward the center of the female red portion S. 
     By utilizing the representative fastening nut  10  described above, the grinding wheel  2  may be mounted to the spindle  3  by the following steps: (1) fitting the grinding wheel  2  onto the spindle  3  until the grinding wheel  2  contacts the flange  3   a  of the spindle  3 , where the grilling wheel  2  is fitted in such a manner that the male threaded portion  3   b  of the spindle  3  is inserted into the mounting hole  2   a  of the grinding wheel  2 , as shown in  FIG. 1 ; and (2) fastening the fastening nut  10  onto the male threaded portion  3   b.    
     In the fastened condition of the fastening nut  10 , each pair of restriction rollers  14  stably prevents the corresponding nut segments  13  form moving in a radially outward direction. Therefore, it is possible to more reliably and stably prevent the movement of the nut segments  13  in comparison with the conventional construction utilizing only a single ball (or roller). In addition, the fastening nut  10  can smoothly rotate in the fastening direction (i.e., right-hand direction) and the loosening direction (i.e., left-hand direction) because the potential movement in the radial direction of the nut segments  13  relative to the fastening nut  10  is reliably prevented. 
     Further, stopper  20  of the representative fastening nut  10  ensures that the fastening nut  10  is fastened onto the male threaded portion  3   b  with the proper orientation of the fastening nut  10  relative to the male threaded potion  3   b . Thus, in order to fasten the fastening nut  10  onto the male treaded portion  3   b , the fastening nut  10  may easily be fitted onto the male threaded portion  3   b  from the side of the insertion hole  11   a  of the base  11 , and may then be rotated in the right-hand direction. As the male threaded portion  3   b  is inserted into the fastening nut  10  from the side of the insertion hole  11   a  of the base  11 , the male threaded portion  3   b  presses the stopper  20  and moves the stopper  20  so as to withdraw the stopper  20  from the female threaded portion S. Consequently, the male threaded portion  3   b  can smoothly engage the fastening nut  10 , i.e., the female threaded portion S. Conversely, in the event that the male threaded portion  3   b  is inserted into the fastening nut  10  from the side of the insertion hole  12   a  of the cover  12 , the male threaded portion  3   b  presses the stopper  20  so as to tilt the stopper  20 . The stopper  20  then further extends into the female threaded portion S so that the male threaded portion  3   b  may not readily move further into the female headed portion S. The fastening nut  10  may therefore be prevented from being completely fastened onto the male threaded portion  3   b  in an attempt to clamp the grinding wheel  2 . As a result, the stopper  20  ensures that the fastening nut  10  is always fastened onto the male threaded portion  3   b  with the fastening nut  10  oriented in a correct direction. Therefore, the fastening nut  10  can be reliably brought to the fastening-unlock condition in order to loosen the fastening nut  10  from the male threaded portion  3   b . Consequently, the fastening nut  10  can reliably implement the loosening assist function. 
     The first representative embodiment described above may be modified in various ways. For example, although the pair of the restriction rollers  14  are incorporated in order to prevent the corresponding nut segment  13  from moving in the radially outward direction, three or more restriction rollers may be used for this purpose. In addition, although the restraining rollers  14  and the auxiliary rollers  15  have cylindrical configurations, they may have spherical configurations. Further, although the relief recesses  13   b  are formed in each nut segment  13 , the relief recesses  13   b  may be formed in the circumferential wall  12   b  of the cover  12  (see, e.g.,  FIGS. 24 and 25 ). Furthermore, the stopper  20  may be eliminated if desired. Although the fastening nut  10  has been described in connection with an application for fixing a grinding wheel  2  to the spindle  3  of a grinder  1 , the fastening nut  10  nay be applied to any other purpose, such as applications in combination with conventional fastening bolts or screws and in combination with anchor bolts used for installation of various machines and apparatus. 
     Second Representative Embodiment 
     A second representative embodiment will now be described with reference to  FIGS. 16 to 21 . In the first representative embodiment described above, the three nut segment  13  constituting a single viral nut to be fastened onto the male threaded portion  3   b  of a spindle  3  are moved in the radial direction in order to lock and release a fastened condition. A fastening nut of the second representative embodiment utilizes wedge members that function so as to press a pressing flange in an axial direction of a male threaded portion against an object (e.g., a grinding wheel  2 ) to be fixed in position in order to establish the fastening condition of the nut. Therefore, the fastening nut of the second representative embodiment is configured as a wedge type fastening nut. 
     Referring to  FIGS. 16 to 21 , the fastening nut  30  has a nut body  31  that includes a female threaded potion  31   a  and a flange portion  31   b . The female threaded portion  31   a  is adapted to be fastened onto the male threaded portion  3   b  of the spindle  3  as described in connection with the first representative embodiment. The flange portion  31   b  extends radially outward from a first end in an axial direction of the female treaded portion  31   a . A pressing flange  32  and a plurality of wedge members  33  (three wedge members are provide in this representative embodiment) are positioned on the outer peripheral side of the nut body  31 . In this embodiment, the female threaded portion  31   a  is configured as a right-hand thread corresponding to the male treaded portion  3   b.    
     The pressing flange  32  is positioned on a second side (opposite to the first side) of the female threaded portion  31   a  and opposes the flange portion  31   b  in the axial direction. Three restricting portions  32   a  extend axially from the inner wall (i.e., the upper wall as viewed in  FIGS. 18 to 21 ) towards the flange portion  31   b . The restricting portions  32   a  are positioned at tri-sectional positions along die circumferential direction. Inner peripheral side parts of the restricting portions  32   a  respectively axially slidably engage guide recesses  31   d  formed in the outer peripheral surface of the nut body  31 . Therefore, the pressing flange  32  can move relative to the nut body  31  in a direction parallel to the axial direction of the nut body  31 , but the pressing flange  32  rotates together with the nut body  31 . In other words, the pressing flange  32  and the nut body  31  always rotate in unison with each other. 
     As shown in  FIGS. 18 to 21 , a seal ring  38  is interposed between the inner peripheral surface of the pressing flange  32  and the outer peripheral surface of the nut body  31 . The seal ring  38  prevents foreign particles from entering a space defined between the flange portion  31   b  of the nut body  31  and the pressing flange  32 . A stopper ring (not shown) may be provided in order to prevent the pressing flange  32  from being removed from the nut body  31 . 
     The wedge members  33  are radially movably disposed between the flange portion  31   b  of the nut body  31  and the pressing flange  32 . The wedge members  33  are positioned at tri-sectional positions in the circumferential direction about the axis of the female threaded portion  31   a . Each of the wedge members  33  has first and second inclined surfaces  33   a  and  33   b  formed on opposite sides in the direction of thickness (i.e., the axial direction). The first inclined surface  33   a  of the wedge members  33  slidably contacts with an inclined surface  31   c  formed on the inner wall of the flange portion  31   b  of the nut body  31 . The inclined surface  31   c  may be formed throughout the circumferential length of the inner wall. The second inclined surface  33   b  of the wedge members  33  respectively slidably contacts with inclined surfaces  32   c  formed on the inner wall of the pressing flange  32   c . Therefore when the wedge members  33  move radially inward, the pressing flange  32  moves in an axial direction away from the flange portion  33   b  so as to be pressed against the grinding wheel  2  (i.e., the object to be fixed in position). As a result, threads of the female threaded portion  31   a  are pressed against the threads of the male threaded portion  3   b  in the axial direction, locking the fastened condition of the fastening nut  30  onto the male threaded portion  3   b.    
     Each of the restricting portions  32   a  of the pressing flange  32  is positioned between each adjacent wedge members  33 . Therefore, the restricting portions  32   a  prevent the wedge portions  33  from moving in a circumferential direction. 
     Similar to the nut segments  13  of the fast representative embodiment, two relief recesses  33   c  are formed in the outer peripheral surface of each of the wedge portions  33 . Each of the relief recesses  33   c  has an arc-shaped configuration in cross-section and has a depth of about 1 mm. As shown in  FIG. 17 , each relief recess  33   c  serves to receive a part of a corresponding restriction roller  35  that will be hereinafter described. 
     An annular operation member  34  is assembled to enclose the wedge members  33  from the outer peripheral side. As shown in  FIGS. 18 to 21 , the flange portion  31   a  of the nut body  31  and the pressing flange  32  ar disposed on the inner side of the operation member  34 . 
     A pair of restriction rollers  35  and an auxiliary roller  36  are disposed between the operation member  34  and each of the wedge members  33 . The auxiliary roller  36  is positioned between the restriction rollers  35  in the circumferential direction and serves to define a possible minimum distance between the restriction rollers  35 . The distance between the restriction rollers  35  (i.e., the distance between the centers of the restriction rollers  35 ) coincides with the distance between the relief recesses  33   c  formed in each wedge member  33 . Therefore, the restriction rollers  35  may simultaneously engage with or disengage from the corresponding relief recesses  33   c.    
     Three engaging projections  34   a  are formed on the inner peripheral wall of the operation member  34  to extend radially inward and to be positioned at this sectional locations along the circumferential direction about the axis of the female threaded portion  31   a . Three engaging projections  32   b  am formed on the pressing flange  32  and respectively oppose the engaging projections  34   a  along the circumferential direction. A compression coil spring  37  is disposed between each engaging projection  34   a  of the operation member  34  and the corresponding engaging  32   b , of the pressing flange  32 . Therefore, the operation member  32  is biased by the compression coil springs  37  in a right-hand direction (i.e., the fastening direction of the fastening nut  30 ) relative to the nut body  31  and the pressing flange  32 . With this arrangement, in order to engage and fasten the fastening nut  30  onto the male threaded portion  3   b , the operation member  34  may be rotated in the right-hand direction (clockwise) as viewed in  FIG. 16 . The rotation of the operation member  34  may be transmitted to the pressing flange  32  via the three groups rollers. Each group of rollers includes a pair of restriction rollers  35  and one auxiliary roller  36 , clamped between the corresponding set of engaging projection  34   a  and engaging projection  32   b . In addition, the operation member  34 , the pressing plate  32 , and the nut body  31 , may rotate in unison with each other in the right-hand direction, since the restricting portions  32   a  of the pressing flange  32  are in engagement with respective guide recesses  31   d  formed in the nut body  31 . The fastening nut  30  may be loosened from the male treaded portion  3   b  by rotating the operation member  34  in the left-hand direction (counter clockwise) as shown in  FIG. 17 . 
     In operation, the fastening nut  30  may be fastened onto the male headed portion  3   b  in such a manner that the male threaded portion  3   b  is inserted into the fastening nut  30  from the side of the pressing flange  32 , as shown in  FIG. 18 . During the fastening process, the pressing flange  32  and evenly the nut body  31  rotate with the operation member  34  in the right-hand direction, i.e., the fastening direction, with the pair of the restriction rollers  35  and the auxiliary roller  36  dame between each of the engaging projections  34   a  of the operation member  34  and the corresponding engaging projection  32   b  of the pressing flange  32 . In addition, during the fastening process, each of the restriction rollers  35  is positioned so as to not engage the corresponding relief recess  33   c . Therefore, each of the wedge members  33  is pressed radially inward toward the center of the fine treaded portion  31   a , so that the pressing flange  32  is held in a position away from the flange portion  31   b  of the nut body  31  in the axial direction. 
     At the final stage of the fastening process of the fastening nut  30 , the pressing flange  32  may be pressed directly against the grinding wheel  2  due to the fastening force attaching the fastening nut  30  onto the male threaded portion  3   b  and due to the wedging actions of the wedge members  33 . As a result, the fastening nut  30  may be fastened onto the male threaded portion  3   b  by a relatively strong force. 
     In order to loosen the fastening nut  30 , the operation member  34  may be rotted in the left-hand direction against the biasing forces of the compression coil springs  37 , as shown in  FIG. 17 . This may cause the rotation of the operation member  34  relative to the pressing flange  32 . As a result, each of the engaging projections  34   a  may no longer apply a clamping force to corresponding set of restriction rollers  35  and the auxiliary roller  36 . The restriction rollers  35  associated with each wedging members  33  may then respectively engage the corresponding relief recesses  33   c  in order to enable the wedging members  33  to move radially outward. The pressing force applied to the grinding wheel  2  from the pressing flange  32  may be weakened, and consequently, the fastening force applied onto the male threaded portion  3   b  by the fastening nut  30  may also be weakened. In this way, the operation member  34 , the pressing flange  32 , and the nut body  31 , can then be rotated in the loosening direction using a relatively small force, after the operation member  34  has been rotated through a predetermined angle against the biasing forces of the compression coil springs  37 , bringing the restriction rollers  35  into engagement with their corresponding relief recesses  33   a.    
     As described above the fastening nut  30  according to the second representative embodiment, even in the event that the fastening nut  30  has been excessively fastened onto the male treaded portion  3   b  clue to the resistance applied by the workpiece to the grinding wheel  2  against the rotation of the rotary tool  1 , can be easily loosened by applying a relatively small force to the operation member  34 , rotating the operation member  34  by a predetermined angle in the loosening direction against the biasing force of the compression coil springs  37 . The wedge members  33  may then become free from restriction. Consequently, the pressing force applied to the grinding wheel  2  by the pressing flange  32  may be lessened or released. 
     In addition, in the fastening nut  30  according to the second representative embodiment, each of the wedge members  33  is arranged in a circumferential about the axis of the male threaded portion  31   a  and is stably prevented from moving in a radial direction by a corresponding pair of restriction rollers  35 . Therefore, it is possible to more reliably and stably prevent the movement of the wedge members  33  in comparison with the conventional construction utilizing only a single ball (or roller). In addition, the fastening nut  30  can smoothly rotate in the fastening direction (i.e., right-hand direction) and the loosening direction (i.e., left-hand direction) because the potential movement in the radial direction of the wedge members  33  relative to the fastening nut  30  is reliably prevented. 
     The second representative embodiment described above may be modified in various ways. For example, although a pair of restriction rollers  35  is incorporated for each of the wedge members  33 , three or more restriction rollers may be incorporated for each of the wedge members  33 . In addition, although the restriction rollers  35  and the auxiliary rollers  36  have cylindrical configurations, the rollers may have spherical configurations. Further, although the relief recesses  33   c  are formed in each wedge member  22 , the relief recesses  33   c  may be formed in the inner circumferential surface of the operation member  34  (see, e.g.,  FIGS. 22 and 23 ). In addition, although the fastening nut  30  has been described in connection with an application for fixing a grinding wheel  2  to the spindle  3  of the grinder  1 , the fastening nut  30  may be applied to any other purposes, such as applications in combination with conventional fastening bolts or screws and in combination with anchor bolts used for installation of various machines and apparatus.