Patent Publication Number: US-2022226704-A1

Title: Golf club and weight piece for golf club

Description:
RELATED APPLICATIONS 
     This application claims the benefit of foreign priority to Japanese Patent Application No. JP2021-005975, filed Jan. 18, 2021, which is incorporated by reference in its entirely. 
     FIELD OF THE INVENTION 
     The present disclosure relates to a golf club and a weight piece for golf club. 
     BACKGROUND OF THE INVENTION 
     Golf club balance may impact golf swing of golfers. Golf club balance that fits golfers is different according to the ability of individual golfers. Thus, it would be convenient if the club balance could be easily adjusted. 
     In order to adjust the club balance of a golf club, the following Patent document 1, for example, discloses installing a weight member in a club shaft on the grip end side. 
     PATENT DOCUMENT 
     
         
         [Patent document 1] Japanese Patent 6601584 
       
    
     SUMMARY OF THE INVENTION 
     When manufacturing a golf club as described above, the weight piece is inserted into an inner space of the club shaft. To facilitate this insertion process, the outer diameter of the weight piece should be formed smaller than the inner diameter of the club shaft. 
     On the other hand, when the outer diameter of the weight piece is smaller than the club shaft, a gap between the weight piece and the club shaft will cause problems such as misalignment of the weight piece and rattling noise. 
     The present disclosure has been made in view of the above circumstances and has a major object to provide a golf club and a weight piece for golf club capable of suppressing misalignment and rattling noise of the weight piece while facilitating the process of inserting the weight piece into a club shaft. 
     In one aspect of the present disclosure, a golf club includes a tubular club shaft having a first end with a first inner diameter, a second end, and an inner peripheral surface defining an inner space of the club shaft, a weight piece installed on a first end side of the club shaft, and a golf club head mounted on a second end side of the club shaft. The weight piece includes an insertion portion located in the inner space of the club shaft, and an engagement portion located outside the inner space of the club shaft to engage the first end of the club shaft. The insertion portion includes a first portion on a first end side, and a second portion on a second end side. The first portion has an outer diameter smaller than the first inner diameter. The second portion includes a large diameter portion having an outer diameter larger than the first inner diameter in a state before being placed in the club shaft, and at least one rigidity-lowered portion that elastically deforms the second portion so that the outer diameter of the large diameter portion becomes smaller when receiving an external force. The second portion is placed in the inner space in an elastically deformed state so that the large diameter portion is at least partially in contact with the inner peripheral surface of the club shaft due to its elastic restoring force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a golf club according to an embodiment of the disclosure; 
         FIG. 2  is a partial cross-sectional view of the golf club on a side of the grip; 
         FIG. 3  is a cross-sectional view of a weight piece according to an embodiment of the disclosure; 
         FIG. 4  is a perspective view of the weight piece according to an embodiment of the disclosure; 
         FIG. 5  is a cross-sectional view taken along the lines V-V of  FIG. 3 ; 
         FIG. 6  is a cross-sectional view of the weight piece according to another embodiment; 
         FIG. 7  is a cross-sectional view of the weight piece according to yet another embodiment; 
         FIG. 8  is a perspective view of the weight piece according to yet another embodiment; 
         FIG. 9  is a cross-sectional view taken along the lines IX-IX of  FIG. 8 ; and 
         FIG. 10  is a cross-sectional view of a second portion of the weight piece according to yet another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present disclosure will be explained below with reference to the accompanying drawings. Note that the same elements or potions are denoted by the same reference numerals throughout the embodiments below, and that redundant description of already described elements is omitted. 
     [Overall Structure of Golf Club] 
       FIG. 1  is a perspective view of a golf club  1  according to an embodiment of the disclosure. As illustrated in  FIG. 1 , the golf club  1  includes a club shaft  2 , a golf club head  3 , a grip  4 , and a weight piece  5 . 
       FIG. 2  is a partial cross-sectional view of the golf club  1  on the grip  4  side, wherein the cross-sectional view is a cross-section including the axial centerline of the club shaft  2 . As illustrated in  FIG. 1  and  FIG. 2 , the club shaft  2  has a tubular shape having an inner space (i) therein. More specifically, the club shaft  2 , in a cross-section perpendicular to the shaft axial direction, has circular outer and inner circumferential faces  2   o  and  2   i . Thus, the club shaft  2  has a cylindrical tubular shape. The club shaft  2 , for example, may be configured by a fiber reinforced plastic or metallic material. 
     [Club Shaft] 
     The club shaft  2 , in the shaft axial direction, includes a first end  2   a  and a second end  2   b  (shown in  FIG. 1 ). In the present embodiment, the club shaft  2  has a tapered shape of the outer and inner diameters both tapering gradually from the first end  2   a  toward the second end  2   b . In another embodiment, the club shaft  2  may have a constant outer diameter and inner diameter. 
     The golf club head  3 , which is for striking a ball, is fixed to the second end  2   b  of the club shaft  2 . The golf club head  3 , for example, is configured as a wood-type head. In another embodiment, the golf club head  3  may be embodied as iron-type, hybrid-type or putter-type. 
     [Grip] 
     The grip  4  is attached to the first end  2   a  side of the club shaft  2 . The grip  4 , for example, includes a tubular grip main body  4   a  that golfers grip, and a grip end face  4   b  located on a one end of the grip main body  4   a . The grip main body  4   a  has a substantially cylindrical tubular shape, more specifically, having a tapered shape tapering according to away from the grip end face  4   b . Additionally, another end side of the grip main body  4   a  is opened (not illustrated) so that the club shaft  2  can be inserted therefrom. Note that the grip end face  4   b  is provided with a through hole  4   c  for removing air from the interior of the golf club  1  when the club shaft  2  is inserted. 
     Although a material of the grip  4  is not particularly limited, a rubber is preferable, for example. As the rubber, for example, natural rubber, styrene butadiene rubber, EPDM, isoprene rubber and mixtures thereof are preferred. In view of moldability of the grip  4 , EPDM and styrene butadiene rubber may further be preferred. 
     [Weight Piece] 
     The weight piece  5  is installed on the first end  2   a  side of the club shaft  2 . Thus, the weight piece  5  is located on an opposite side to the golf club head  3  in the shaft axial direction. Such a weight piece  5  can be helpful to provide a counterweighted golf club  1 . 
     As illustrated in  FIG. 2 , the weight piece  5  according to the present embodiment includes an insertion portion  6  and an engagement portion  7 . 
     [Insertion Portion] 
     The insertion portion  6  is a portion that is located in the inner space (i) of the shaft  2 , and includes a first portion  10  on the first end  2   a  side and a second portion  20  on the second end  2   b  side. On the other hand, the engagement portion  7  is located outside the inner space (i) of the club shaft  2  to engage the first end  2   a  of the club shaft  1 . 
     [First Portion] 
       FIG. 3  illustrates the club shaft  2  and the weight piece  5  in the state before being placed in the club shaft  2 .  FIG. 4  is a perspective view of the weight piece  5  in the state before being placed in the club shaft  2 . As illustrated in  FIGS. 2 to 4 , the first portion  10 , for example, has an outer diameter D 1  which is smaller than a first inner diameter dl of the club shaft  2  at the first end  2   a  side. The first portion  10  according to the present embodiment has a columnar shape. In addition, the first portion  10  according to the present embodiment extends in the shaft axial direction with a substantially constant outer diameter D 1 . In another embodiment, the first portion  10  may be polygonal prismatic and the outer diameter D 1  may change in the shaft axial direction. 
     The first portion  10 , for example, includes a metal weight body  101  and an elastic body  102  made of plastic, elastomer or rubber covering the weight body  101  at least partially. The elastic body  102  according to the present embodiment, for example, is made of a plastic. The weight body  101 , for example, has a columnar shape. Preferably, the weight body  101  and the elastic body  102  are integrally formed in advance by insert molding, etc., for example. 
     When the first portion  10  includes the above-mentioned metal weight body  101 , a small volume can provide a sufficiently large weight of the weight piece  5 . In addition, since the surface of the first portion  10  is formed by the elastic body  102 , it is preferable in that damage to the shaft  2  can be suppressed when the shaft  2  comes into contact with the first portion  10 . 
     [Second Portion] 
     The second portion  20  is located on the second end  2   b  side of the first portion  10 . The second portion  20  according to the present embodiment is formed in a cylindrical body (conical cylinder body) with a hollow portion  24  on a center side in the shaft radial direction. Specifically, the second portion  20  according to the present embodiment is a cylindrical body obtained by extending the elastic body  102  of the first portion  10  to the second end  2   b  side. Thus, the second portion  20  according to the present embodiment is made of an elastic material made of plastic, elastomer or rubber. 
     As illustrated in  FIG. 3 , the second portion  20  includes a large diameter portion  22  having an outer diameter D 2  larger than the first inner diameter dl under the state before being placed in the club shaft  2 . The second portion  20  according to the present embodiment, for example includes an enlarged diameter portion  20 A whose outer diameter, in a state before being placed in the club shaft  2 , increasing gradually toward the second end  2   b . The large diameter portion  22  is formed on an end side of the enlarged diameter portion  20 A. The enlarged diameter portion  20 A, for example, forms a conical surface. 
     In addition, the second portion  20  is provided with at least one rigidity-lowered portion  21 . As the rigidity-lowered portion  21 , for example, one or more slits  21 A may be adopted. The slits  21 A can locally reduce stiffness of the second portion  20  by cutting out the same. In some preferred embodiments, the second portion  20  is provided with a plurality of slits  21 A extending in the shaft axial direction. By providing a plurality of slits  21 A, the second portion  20  is divided into a plurality of claw pieces  26  that extends in the shaft axial direction and is elastically deformable. 
     The second portion  20  as described above can be elastically deformed so that its outer diameter (the outer diameter D 2  of the large diameter portion  22 ) becomes smaller when receiving an external force. For example, by pushing the claw pieces  26  toward the center side in the shaft radial direction with fingers, each claw piece  26  is elastically bent and deformed from the vicinity of its root side. As a result, the outer diameter D 2  of the large diameter portion  22  can be small easily. 
     Although not particularly limited, in order to easily deform the claw pieces  26 , a length L along the shaft axal direction of the slits  21 A, for example, is preferably equal to or more than 3.0 mm, more preferably equal to or more than 4.0 mm, still further preferably equal to or more than 5.0 mm From the same viewpoint, a width W (the dimension orthogonal to the length L) of the slits  21 A, for example, is preferably equal to or more than 0.5 mm, more preferably equal to or more than 1.0 mm, still further preferably equal to or more than 1.5 mm. 
     [Engagement Portion] 
     The engagement portion  7  engages the first end  2   a  of the shaft  2 , and thus the engagement portion  7  cannot enter the inner space (i) of the club shaft  2 . This can regulate the insertion position of the weight piece  5  into the club shaft  2  and stabilize the position of the weight piece  5 . The engagement portion  7  according to the present embodiment is formed into a flange having an outer diameter D 3  larger than the first inner diameter dl of the club shaft  2 . The engagement portion  7  can take various forms as long as it has a shape that engages with the first end  2   a  of the club shaft  2 . 
     [Process of Inserting Weight Piece into Shaft] 
     The process of inserting the weight piece  5  into the inner space (i) of the club shaft  2  is performed by the following procedure, for example. First, give an external force to the second portion  20  of the weight piece  5  by, for example, jig, fingers, or other means to deform the second portion  20  elastically so that the outer diameter of the second portion  20  becomes smaller than the first inner diameter dl of the club shaft  2 . Next, in this state, the second portion  20  of the weight piece  5  is pushed into the inner space (i) from the first end  2   a  side of the club shaft  2 . This allows the insertion portion  6  of the weight piece  5  to be easily inserted into the inner space (i) of the club shaft  2 . Further, as the insertion of the insertion portion  6  into the shaft  2  progresses, the engagement portion  7  contacts the first end  2   a  of the club shaft  2  and the insertion position of the weight piece  5  into the shaft  2  is restricted. 
     Furthermore, when the insertion portion  6  is completely inserted into the inner space (i) of the club shaft  2 , the second portion  20  is released from an external force and tries to elastically restore its original shape. However, since the outer diameter D 2  of the large diameter portion  22  is originally larger than the first inner diameter dl of the club shaft  2 , the second portion  20  is placed inside the inner space (i) of the club shaft  2  in an elastically deformed state (not completely restored to its original shape). Thus, the large diameter portion  22  of the second portion  20  is expanded by its elastic restoring force, and at least a part of it contacts with the inner peripheral surface  2   i  of the shaft  2 . Therefore, contact friction occurs between the weight piece  5  and the inner peripheral surface  2   i  of the shaft  2  so that the position of the weight piece  5  can be stable. 
     As described above, the golf club  1  according to the present disclosure can suppress the misalignment and rattling noise of the weight piece  5  while facilitating the process of inserting the weight piece  5  into the club shaft  2 . 
     By the way, the first inner diameter dl of the shaft  2  is generally different for each type of golf club  1 . In some preferred embodiments, the outer diameter D 3  of the engagement portion  7  and the outer diameter D 2  of the large diameter portion  22  of the second portion  20  may be formed larger than the first inner diameter dl of some types of shafts  2 , and the outer diameter D 1  of the first portion  10  may be formed smaller than the first inner diameter dl of some types of shafts  2 . In this case, the weight piece  5  can be attached to various types of shafts  2  with different first inner diameters dl, which can improve the versatility of the weight piece  5 . 
     Next, some more preferred embodiments of the present invention will be described. 
     [Interval of Rigidity-Lowered Portion (FIG.  5 )] 
       FIG. 5  illustrates a cross-sectional view taken along the line V-V of  FIG. 3 . As illustrated in  FIG. 5 , the rigidity-lowered portion  21  (the slits  21 A) may be formed at an equal interval in the shaft circumferential direction of the second portion  20 . According to such an embodiment, the flexural rigidity of each claw piece  26  of the second portion  20  may be made uniform, and the elastic restoring force of each claw piece  26  may work on the inner peripheral surface  2   i  of the club shaft  2  in a well-balanced manner in the shaft circumferential direction. Thus, the weight piece  5  according to the present embodiment can be held more stably in the inner space (i) of the club shaft  2 . 
     In  FIG. 5 , as such an example, four slits  21 A each having the same shape are arranged at a 90-degree interval in the shaft circumferential direction. Further, when the weight piece  5  is attached to the inner space (i) of the club shaft  2 , it is preferable that the center of gravity g of the second portion  20  (shown for convenience in  FIG. 5 ) is formed on the center line of the club shaft. As a result, the above effect can be obtained more reliably. 
     In addition, as illustrated in  FIG. 5 , a cross-sectional shape of each claw piece  26  perpendicular to the shaft axial direction may decrease toward the second end  2   b . Specifically, the circumferential length (a) and/or the thickness (b) in the shaft radial direction of each claw piece  26  may be formed so as to decrease continuously or stepwisely toward the second end  2   b  of the club shaft  2 . In such an embodiment, the center of gravity of the second portion  20  may be located on the first end  2   a  side in the shaft axial direction, so that the counterbalance effect can further be enhanced. 
     [Other Embodiments of Weight Piece (FIG.  6 )] 
       FIG. 6  illustrates a cross-sectional view of the weight piece  5  according to another embodiment. The weight piece  5  differs from  FIG. 3  in that the outer diameter D 1  of the first portion  10  increases continuously toward the second end  2   b . Thus, the first portion  10  has a conical outer surface. In addition, the weight piece  5  is formed so that the conical outer surface is continuous from the first portion  10  to the second portion  20 . Such a weight piece  5  can be installed on various shafts with different first inner diameters dl and be highly versatile. 
     [Yet Another Embodiment of Weight Piece (FIG.  6 )] 
     As illustrated in  FIG. 6 , the first portion  10  of the weight piece  5  include an outer surface being provided with at least one protrusion  103  protruding in the shaft radial direction which is capable of contacting with inner peripheral surface  2   i  of the club shaft  2 . The protrusion  103 , for example, has a protrusion height increasing continuously toward the engagement portion  7 . This allows the protrusion  103  to be easily inserted into the club shaft  2 . Preferably, a plurality of protrusions  103  may be provided at an equal interval in the shaft circumferential direction. 
     In the weight piece  5  according to this embodiment, when the first portion  10  is placed in the inner space (i) of the club shaft  2 , the protrusions  103  and/or the inner peripheral surface  2   i  of the club shaft  2  is deformed, so that a high contact pressure may be locally obtained therebetween. Thus, the weight piece  5  can be more securely fixed inside the club shaft  2 . Note that the protrusions  103  can be applied to the weight piece  5  in the shape of  FIG. 3 . 
     [Yet Another Embodiment of Weight Piece (FIG.  7 )] 
       FIG. 7  illustrates a cross-sectional view of the weight piece  5  according to yet another embodiment. the weight piece  5  differs from  FIG. 3  in that the second portion  20  includes a small diameter portion  28 . The small diameter portion  28  is provided on an end  20   e  of the second portion  20  on the second end  2   b  side. Further, in a state of the weight piece  5  before being placed in the club shaft  2 , an outer diameter D 4  of the small diameter portion  28  is smaller than the first inner diameter dl of the club shaft  2 . 
     In some preferred embodiments, the small diameter portion  28  tapers so that the outer diameter continuously decreases toward the second end  2   b  side. In addition, the slits  21 A are formed from the large diameter portion  22  to the small diameter portion  28 , for example. 
     According to the weight piece  5  shown in  FIG. 7 , it may be easier to insert the weight piece  5  into the club shaft  2 , and the productivity of golf club  1  can be improved. That is, since the weight piece  5  has the end  20   e  of the second portion  20  with the small diameter portion  28  described above, it is not necessary to give an external force to the second portion  20  in advance to reduce its outer diameter when inserting the weight piece  5  into the club shaft  2 . For example, when inserting the small diameter portion  28  into the inner space (i) of the club shaft  2 , the outer peripheral surface of the large diameter portion  22  comes into contact with the inner peripheral surface  2   i  of the club shaft  2 , and receives an inward force in the shaft radial direction from the inner peripheral surface  2   i . This allows the second portion  20  to be easily inserted into the inner space (i) of the club shaft  2  while gradually shrinking its outer diameter. 
     [Yet Another Embodiment of Weight Piece (FIG.  8 )] 
       FIG. 8  illustrates a perspective view of the weight piece  5  according to yet another embodiment.  FIG. 9  is a cross-sectional view taken along the lines IX-IX of  FIG. 8 . As illustrated in  FIG. 8  and  FIG. 9 , in the weight piece  5  according to this embodiment, the rigidity-lowered portions  21  of the second portion  20  are formed into thin-walled portions  21 B (instead of the slits  21 A). The thin-walled portions  21 B, for example, connect the adjacent claw pieces  26  and  26  with a wall thickness smaller than that of the claw pieces  26 , and extend in the shaft axial direction. In this embodiment, the thin-walled portions  21 B have a thickness in the shaft radial direction equal to or less than 50% of the wall thickness of the claw pieces  26 , for example. 
     The thin-walled portions  21 B as described above can easily deformed itself when an external force is applied. Thus, in this embodiment as well, when an external force is given to the second portion  20 , the outer diameter of the large diameter portion  22  can be elastically deformed to be small. Further, when the rigidity-lowered portions  21  are configured as the thin-walled portions  21 B, it may be possible to generate a larger elastic restoring force in each of the claw pieces  26  than in the case of the slits  21 A. Thus, the position of the weight piece  5  can be more stable. 
     In this embodiment, the thin-walled portions  21 B connect the claw pieces  26  at a position recessed from the radially outer surface of the shaft of the second portion  20 . Alternatively, the thin-walled portions  21 B may be provided in a recessed position from the radially inner surface of the shaft of the second portion  20 . 
       FIG. 10  illustrates a cross-sectional view (equivalent to IX-IX line cross section of  FIG. 8 ) of the second portion  20  of the weight piece  5  according to yet another embodiment. As illustrated in  FIG. 10 , in this weight piece  5 , instead of the slits  21 A, the rigidity-lowered portions  21  of the second portion  20  are formed into grooves  21 C. The grooves  21 C are recessed in the shaft radial direction between the adjacent claw pieces  26  and  26  and extend in the shaft axial direction. In addition, the grooves  21 C, for example, connect the adjacent claw pieces  26  with a wall thickness equal to or less than the wall thickness of the claw pieces  26 . 
     Therefore, even in this embodiment, when an external force is applied to the second portion  20 , the grooves  21 C are locally deformed, and the outer diameter of the large diameter portion  22  can be elastically deformed to a small extent. Further, when the rigidity-lowered portions  21  are configured as the grooves  21 C, each claw piece  26  can generate a larger elastic restoring force than the case of the slits  21 A. Thus, the position of the weight piece  5  can be more stable. 
     As the rigidity-lowered portions  21 , it is noted that the thin-walled portions  21 B or the grooves  21 C may be used together with the slits  21 A. 
     While the particularly preferable embodiments in accordance with the present disclosure have been described in detail, the present disclosure is not limited to the illustrated embodiments, but can be modified and carried out in various aspects within the scope of the disclosure. 
     The following clauses are disclosed regarding the above-described embodiments. 
     [Clause 1] 
     A golf club comprising:
         a tubular club shaft having a first end with a first inner diameter, a second end, and an inner peripheral surface defining an inner space of the club shaft;   a weight piece installed on a first end side of the club shaft; and   a golf club head mounted on a second end side of the club shaft,   wherein   the weight piece comprises
           an insertion portion located in the inner space of the club shaft, and   an engagement portion located outside the inner space of the club shaft to engage the first end of the club shaft,   
           the insertion portion comprises
           a first portion on a first end side, and   a second portion on a second end side,   
           the first portion has an outer diameter smaller than the first inner diameter,   the second portion comprises
           a large diameter portion having an outer diameter larger than the first inner diameter in a state before being placed in the club shaft, and   at least one rigidity-lowered portion that elastically deforms the second portion so that the outer diameter of the large diameter portion becomes smaller when receiving an external force, and   
           the second portion is placed in the inner space in an elastically deformed state so that the large diameter portion is at least partially in contact with the inner peripheral surface of the club shaft due to its elastic restoring force.       

     [Clause 2] 
     The golf club according to clause 1, wherein
         the at least one rigidity-lowered portion comprises at least one slit.       

     [Clause 3] 
     The golf club according to clause 1 or 2, wherein
         the second portion has a cylindrical body with a hollow portion on a center side in a shaft radial direction, and   the at least one rigidity-lowered portion extends on the cylindrical body in a shaft axial direction.       

     [Clause 4] 
     The golf club according to any one of clauses 1 to 3, wherein
         the at least one rigidity-lowered portion comprises a plurality of rigidity-lowered portions.       

     [Clause 5] 
     The golf club according to any one of clauses 1 to 4, wherein
         the at least one rigidity-lowered portion comprises a plurality of rigidity-lowered portion formed at an equal interval in a shaft circumferential direction of the second portion.       

     [Clause 6] 
     The golf club according to any one of clauses 1 to 5, wherein
         the second portion comprises an enlarged diameter portion whose outer diameter, in a state before being placed in the club shaft, increasing toward the second end.       

     [Clause 7] 
     The golf club according to any one of clauses 1 to 6, wherein
         the second portion comprises a small diameter portion whose outer diameter at an end on the second end side, in a state before being placed on the club shaft, is smaller than the first inner diameter.       

     [Clause 8] 
     The golf club according to clause 2, wherein
         the second portion is divided into a plurality of deformable claw pieces extending in a shaft axial direction by the at least one slit, and   a cross-sectional shape of each claw piece perpendicular to the shaft axial direction decreases toward the second end.       

     [Clause 9] 
     The golf club according to any one of clauses 1 to 8, wherein
         the first portion comprises an outer surface being provided with at least one protrusion protruding in a shaft radial direction to contact with inner peripheral surface of the club shaft.       

     [Clause 10] 
     The golf club according to clause 9, wherein
         the at least one protrusion has a protrusion height increasing toward the engagement portion.       

     [Clause 11] 
     The golf club according to any one of clauses 1 to 10, wherein
         the first portion comprises a metal weight body and an elastic body made of resin, elastomer or rubber covering the weight body at least partially.       

     [Clause 12] 
     The golf club according to any one of clauses 1 to 11, wherein
         the at least one rigidity-lowered portion comprises a thin-walled portion or groove.       

     [Clause 13] 
     A weight piece for golf club having a tubular club shaft having a first end with a first inner diameter, a second end, and an inner surface therein, the weight piece adapted to be installed on a first end side of the club shaft,
         the weight piece comprising:
           an insertion portion to be located in the inner space of the club shaft, and   an engagement portion to be located outside the inner space of the club shaft to engage the first end of the club shaft,
 
wherein
   
           the insertion portion comprises
           a first portion on a first end side, and   a second portion on a second end side, and   
           the second portion comprises at least one rigidity-lowered portion that elastically deforms the second portion so that the outer diameter of the large diameter portion becomes smaller when receiving an external force.       

     [Clause 14] 
     The weight piece for golf club according to clause 13, wherein
         the at least one rigidity-lowered portion comprises at least one slit.       

     [Clause 15] 
     The weight piece for golf club according to clause 13 or 14, wherein
         the at least one rigidity-lowered portion comprises a thin-walled portion or groove.       

     [Clause 16] 
     The weight piece for golf club according to any one of clauses 13 to 15, wherein
         the at least one rigidity-lowered portion comprises a plurality of rigidity-lowered portions.       

     [Clause 17] 
     The weight piece for golf club according to any one of clauses 13 to 16, wherein
         the at least one rigidity-lowered portion comprises a plurality of rigidity-lowered portion formed at an equal interval in a shaft circumferential direction of the second portion.       

     [Clause 18] 
     The weight piece for golf club according to any one of clauses 13 to 17, wherein
         the second portion comprises an enlarged diameter portion whose outer diameter increasing toward the second end.       

     [Clause 19] 
     The weight piece for golf club according to any one of clauses 13 to 18, wherein
         the second portion comprises a small diameter portion whose outer diameter at an end on a second end side is smaller than the first inner diameter of the club shaft.       

     [Clause 20] 
     The weight piece for golf club according to any one of clauses 13 to 19, wherein
         the second portion is divided into a plurality of deformable claw pieces extending in a shaft axial direction by the at least one slit, and   a cross-sectional shape of each claw piece perpendicular to a shaft axial direction decreases toward the second end.