Abstract:
A head ( 2 ) includes a head body ( 4 ), an additional member ( 6 ) in which a contour shape obtained by a projection onto a plane has a rotational symmetric axis (z 1 ), and a holding mechanism ( 28 ) for holding the additional member ( 6 ). The head body ( 4 ) has a recess portion ( 18 ) in which at least a part of the additional member ( 6 ) can be fitted. The holding mechanism ( 28 ) is constituted to enable a mutual transition of a holding state in which the additional member ( 6 ) is held in the recess portion ( 18 ) and a releasing state in which the hold is released. The recess portion ( 18 ) inhibits a rotation around the rotational symmetric axis (z 1 ) of the additional member ( 6 ) in the holding state. The additional member ( 6 ) is rotatable around the rotational symmetric axis (z 1 ) in the releasing state. A phase of the additional member ( 6 ) in the holding state is changed so that a position of a center of gravity of the head can be varied.

Description:
[0001]    This application claims priority on Patent Application No. 2007-289629 filed in JAPAN on Nov. 7, 2007, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a golf club head. 
         [0004]    2. Description of the Related Art 
         [0005]    As a characteristic of a golf club head, a position of a center of gravity is important. Depending on the position of the center of gravity, for example, a position of a sweet spot SS or a moment of inertia might fluctuate. The position of the center of gravity of the head influences a flight distance and a trajectory. 
         [0006]    An optimum position of the center of gravity is varied every golf player. Also in the same golf player, the optimum position of the center of gravity might be changed depending on a playing condition. 
         [0007]    There has been proposed a golf club head capable of changing a position of a center of gravity. Japanese Laid-Open Patent Publication No. 9-28844 has disclosed a golf club head including a weight member which is screwed into a screw stock. The weight member can be moved through a rotation of the screw stock. Japanese Laid-Open Patent Publication No. 2006-288882 has disclosed a golf club head in which a plurality of weights is disposed in a body of a head portion and a position of a center of gravity can be changed through an exchange of the weights. Japanese Laid-Open Patent Publication No. 2006-320493 has disclosed a golf club head in which a position of a center of gravity can be changed through a movement of a weight member. The movement includes a rotating movement. Japanese Laid-Open Patent Publication No. 2006-505367 has disclosed a golf club head having a removable weight. WO2004/043549 A1 corresponds to the Japanese Laid-Open Patent Publication No. 2006-505367. 
       SUMMARY OF THE INVENTION 
       [0008]    In order to change a position of a center of gravity, a combination of a head body and a center-of-gravity adjusting member is effective. In use of a golf club, it is demanded that the center-of-gravity adjusting member is fixed to the head body. A golf club head capable of easily changing the position of the center of gravity while meeting the demand is preferable. 
         [0009]    It is an object of the present invention to provide a head capable of enhancing an easiness of a change in a position of a center of gravity and reliably fixing a center-of-gravity adjusting member. 
         [0010]    A golf club head according to the present invention includes a head body, an additional member in which a contour shape obtained by a projection onto a plane has a rotational symmetric axis, and a holding mechanism for holding the additional member. The head body has a recess portion in which at least a part of the additional member can be fitted. The holding mechanism is constituted to enable a mutual transition of a holding state in which the additional member is held in the recess portion and a releasing state in which the hold is released. The recess portion inhibits a rotation around the rotational symmetric axis of the additional member in the holding state. The additional member is rotatable around the rotational symmetric axis in the releasing state. A phase of the additional member in the holding state is changed so that a position of a center of gravity of the head can be varied. 
         [0011]    It is preferable that the contour shape of the additional member should be N-fold rotational symmetric, and N should be a natural number of three or more. 
         [0012]    It is preferable that a through hole should be provided on a bottom face portion of the recess portion. It is preferable that a bar-shaped member which can be inserted into the through hole should be protruded from an internal surface of the additional member and one of ends of the bar-shaped member should be provided with the additional member. It is preferable that the other end of the bar-shaped member should be provided with an engaging portion which cannot be inserted into the through hole. It is preferable that a central axis of the bar-shaped member should be coincident with the rotational symmetric axis of the additional member. It is preferable that the bar-shaped member should be inserted into the through hole. It is preferable that the internal surface of the additional member should abut on the bottom face of the recess portion in the holding state. 
         [0013]    It is preferable that the additional member should be formed by at least two materials having different specific gravities from each other. It is preferable that an elastic member should be provided between an internal surface of the bottom face portion and the engaging portion. It is preferable that the elastic member should perform biasing to increase an interval between the internal surface of the bottom face portion and the engaging portion in the holding state. It is preferable that the elastic member should be elastically deformable to take the releasing state. 
         [0014]    It is preferable that an elastic member should be disposed in at least a part between a side surface of the additional member and a wall surface of the recess portion. 
         [0015]    The position of the center of gravity can easily be changed through the rotation of the additional member. Moreover, the additional member can be reliably fixed through the recess portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a perspective view showing a golf club head according to an embodiment of the present invention, 
           [0017]      FIG. 2  is a perspective view showing the golf club head of  FIG. 1  as seen in another direction, 
           [0018]      FIG. 3  is a perspective view showing a head body in the golf club head of  FIG. 1 , 
           [0019]      FIG. 4  is a perspective view showing an additional member in the golf club head of  FIG. 1 , 
           [0020]      FIG. 5  is a perspective view showing the additional member of  FIG. 4  as seen from a back side, 
           [0021]      FIG. 6  is a sectional view taken along a VI-Vi line in  FIG. 2 , 
           [0022]      FIG. 7  is a sectional view showing a releasing state, 
           [0023]      FIG. 8  is a view for explaining a procedure for assembling the head, 
           [0024]      FIG. 9  is a sectional view showing a head according to another embodiment, 
           [0025]      FIG. 10  is a view for explaining a procedure for assembling a head according to a further embodiment, 
           [0026]      FIG. 11  is a perspective view showing an additional member according to the further embodiment, 
           [0027]      FIG. 12  is a view showing the head according to the further embodiment as seen from a back side, 
           [0028]      FIG. 13  is a sectional view showing the head of  FIG. 12 , 
           [0029]      FIG. 14  is a sectional view showing a part of the head according to the further embodiment, and 
           [0030]      FIG. 15  is a view for explaining various additional members. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    The present invention will be described below in detail based on preferred embodiments with reference to the drawings. 
         [0032]      FIG. 1  is a perspective view seen from a face side and  FIG. 2  is a perspective view seen from a sole side. In the present embodiment, a head  2  is a golf club head of a wood type. The head  2  includes a head body  4  and an additional member  6 . 
         [0033]    The head body  4  has a face portion  8 , a sole portion  10 , a crown portion  12 , a side portion  14  and a hosel portion  16 . An inner part of the head body  4  is hollow, which is not shown. 
         [0034]      FIG. 3  is a perspective view showing the head body  4 . The head body  4  has a recess portion  18 . The recess portion  18  is provided in the sole portion  10 . The additional member  6  can be fitted in the recess portion  18 . The whole additional member  6  can be fitted in the recess portion  18 . In the head  2 , the whole additional member  6  is accommodated in the recess portion  18 . 
         [0035]    The recess portion  18  takes a planer shape of a cross. The additional member  6  takes a planer shape of a cross. The planar shape of the recess portion  18  corresponds to that of the additional member  6 . 
         [0036]    In the additional member  6 , a contour shape obtained by a projection onto a plane has a rotational symmetry. In the additional member  6 , the contour shape obtained by the projection onto the plane has a rotational symmetric axis z 1 . The details of the rotational symmetry and the rotational symmetric axis z 1  will be described below. 
         [0037]    In the recess portion  18 , a contour shape obtained by a projection onto a plane has a rotational symmetry. In the recess portion  18 , the contour shape obtained by the projection onto the plane has a rotational symmetric axis z 2 . The details of the rotational symmetry and the rotational symmetric axis z 2  will be described below. 
         [0038]      FIGS. 4 and 5  are perspective views showing the additional member  6 .  FIG. 4  is a perspective view showing the additional member  6  seen from a surface side.  FIG. 5  is a perspective view showing the additional member  6  seen from a back side. The additional member  6  has an external surface  20  and an internal surface  22 . In a state in which the additional member  6  is attached to the recess portion  18 , the external surface  20  is exposed to an outside. In the state in which the additional member  6  is attached to the recess portion  18 , the internal surface  22  abuts on a bottom face of the recess portion  18 . 
         [0039]    As shown in  FIGS. 4 and 5 , the additional member  6  has a first extended portion  6   a  which is extended in a first direction, a second extended portion  6   b  which is extended in a second direction, a third extended portion  6   c  which is extended in a third direction, and a fourth extended portion  6   d  which is extended in a fourth direction. An angle defined by the extending direction of the first extended portion  6   a  and that of the second extended portion  6   b  is 90 degrees. An angle defined by the extending direction of the second extended portion  6   b  and that of the third extended portion  6   c  is 90 degrees. An angle defined by the extending direction of the third extended portion  6   c  and that of the fourth extended portion  6   d  is 90 degrees. An angle defined by the extending direction of the fourth extended portion  6   d  and that of the first extended portion  6   a  is 90 degrees. The extending direction of the first extended portion  6   a  is reverse to that of the third extended portion  6   c.  The extending direction of the second extended portion  6   b  is reverse to that of the fourth extended portion  6   d.    
         [0040]    The additional member  6  has a body  24  and a separate member  26 . The separate member  26  is fitted in a recess portion provided on the body  24 . A material of the body  24  has a different specific gravity from that of a material of the separate member  26 . Thus, the additional member  6  is formed by at least two materials having different specific gravities from each other. A center of gravity of the additional member  6  is not present on the rotational symmetric axis z 1 . The rotational symmetric axis z 1  does not pass through the separate member  26 . 
         [0041]      FIG. 6  is a sectional view taken along a VI-VI line of  FIG. 2 . In  FIG. 6 , only the vicinity of the additional member  6  is shown and the other portions are not shown. As described above, the head  2  is hollow. An upper side in  FIG. 6  indicates the hollow portion of the head  2  and a lower side in  FIG. 6  indicates the outside of the head  2 . 
         [0042]    The head  2  includes a holding mechanism  28  for holding the additional member  6 . The holding mechanism  28  has a bar-shaped member  30  and an elastic member  32 . In the present embodiment, the elastic member  32  is a coil spring. The coil spring is a compression spring. 
         [0043]    The bar-shaped member  30  is protruded from the internal surface  22  of the additional member  6 . The additional member  6  is provided on one of ends of the bar-shaped member  30 . The bar-shaped member  30  is a round bar. The bar-shaped member  30  and the additional member  6  are coupled to each other with a screw mechanism. A female screw hole  34  is provided on a center of the internal surface  22  of the additional member  6 . A male screw portion  36  is provided on one of the ends of the bar-shaped member  30 . The female screw hole  34  and the male screw portion  36  are screwed to each other. 
         [0044]    A through hole  40  is provided on a bottom face portion  38  of the recess portion  18 . The bar-shaped member  30  is inserted into the through hole  40 . An inside diameter of the through hole  40  is greater than an outside diameter of the bar-shaped member  30 . A central axis of the through hole  40  is coincident with the rotational symmetric axis z 2 . 
         [0045]    An engaging portion  42  is provided on the other end of the bar-shaped member  30 . In a state in which the bar-shaped member  30  and the engaging portion  42  are coupled to each other, the engaging portion  42  cannot be inserted through the through hole  40 . The engaging portion  42  prevents the bar-shaped member  30  from dropping out. 
         [0046]    A central axis of the bar-shaped member  30  is coincident with the rotational symmetric axis z 1 . A play is present between the bar-shaped member  30  and the through hole  40 . Therefore, the rotational symmetric axes z 2  and z 1  are not always coincident with each other. A rotating member R 1  which will be described below can be reciprocated in an axial direction of the through hole  40  with a posture in which the rotational symmetric axes z 1  and z 2  are coincident with each other. 
         [0047]    An inside diameter of the elastic member  32  to be the coil spring is greater than an outside diameter of the bar-shaped member  30 . The bar-shaped member  30  is inserted into an inside of the elastic member  32 . 
         [0048]    The elastic member  32  is provided between an internal surface  44  of the bottom face portion  38  and the engaging portion  42 . One of ends of the elastic member  32  abuts on the internal surface  44  of the bottom face portion  38 . The other end of the elastic member  32  abuts on the engaging portion  42 . In an integrating state with the bar-shaped member  30 , the engaging portion  42  cannot be inserted through the elastic member  32 . A maximum diameter of the engaging portion  42  is greater than an inside diameter of the elastic member  32 . 
         [0049]      FIGS. 2 and 6  are views showing a holding state. When a golf play is to be carried out with a golf club having the head  2  attached thereto, the head  2  is brought into the holding state. On the other hand,  FIG. 7  is a sectional view showing a releasing state. When the position of the center of gravity of the head  2  is to be adjusted, the head  2  is brought into the releasing state. 
         [0050]    As described above, the elastic member  32  is the compression spring. In the holding state, the elastic member  32  tries to be extended more greatly. In the holding state shown in  FIG. 6 , the elastic member  32  performs biasing to increase an interval between the internal surface  44  of the bottom face portion  38  and the engaging portion  42 . By the biasing force, the internal surface  22  of the additional member  6  and the bottom face  46  of the recess portion  18  abut on each other with a pressure. By the biasing force, the additional member  6  is reliably fitted in the recess portion  18 . 
         [0051]    In the head  2 , it is possible to carry out a mutual transition of the holding state ( FIG. 6 ) and the releasing state ( FIG. 7 ). In order to carry out a transition from the holding state to the releasing state, it is preferable to apply an external force F 1  (see  FIG. 7 ) resisting the biasing force of the elastic member  32  to the additional member  6 , thereby pulling the additional member  6  to an outside of the head  2  (a lower side in  FIG. 6 ). In the releasing state of  FIG. 7 , the elastic member  32  is further compressed as compared with the holding state. In the releasing state, the additional member  6  perfectly slips out of the recess portion  18 . In the releasing state, the recess portion  18  is disengaged from the additional member  6 . In the releasing state, the additional member  6 -can be rotated around the rotational symmetric axis z 1 . 
         [0052]    The center of gravity of the rotating member R 1  constituted by the additional member  6 , the bar-shaped member  30  and the engaging portion  42  is not present on the rotational symmetric axis z 1 . When the additional member  6  is rotated, the rotating member R 1  is rotated. The rotating member R 1  is rotated around the rotational symmetric axis z 1  so that the center of gravity of the head  2  is moved. 
         [0053]    In the releasing state, the rotating member R 1  can be rotated around the rotational symmetric axis z 1 . By the presence of the engaging portion  42 , the rotating member R 1  does not drop out of the head body  4  in the releasing state. In the head  2 , it is possible to change the position of the center of gravity of the head  2  without removing the rotating member R 1 . By simply pulling and rotating the rotating member R 1 , it is possible to change the position of the center of gravity of the head  2 . 
         [0054]    The contour shape of the additional member  6  obtained by a projection onto a plane is four-fold rotational symmetric. The additional member  6  can take four types of phases in the holding state. In any of the phases, the additional member  6  can be fitted in the recess portion  18 . In the holding state, the position of the center of gravity of the head  2  can be set into four ways. 
         [0055]    An amount of compressive deformation of the elastic member  32  has a limit. It is possible to implement the releasing state without reaching the limit of the amount of compressive deformation of the elastic member  32 . The elastic member  32  can be subjected to the compressive deformation to the extent that the releasing state can be brought. More specifically, the elastic member  32  is elastically deformable to take the releasing state. 
         [0056]    In order to maintain the releasing state, it is necessary to continuously apply the external force F 1  to the additional member  6 . The additional member  6  is rotated with the external force F 1  maintained (see an arrow Y 1  in  FIG. 7 ). 
         [0057]    When the external force F 1  is eliminated, the additional member  6  is attracted to the head body  4  by the biasing force of the elastic member  32 . When the external force F 1  is eliminated, the holding state can be recovered. In order to recover the holding state, it is necessary for the additional member  6  to be fitted into the recess portion  18 . In order to recover the holding state, the additional member  6  is rotated to be fitted into the recess portion  18 . 
         [0058]    In the holding state, the additional member  6  cannot be rotated around the rotational symmetric axis z 1 . In the holding state, the additional member  6  is engaged with the recess portion  18  in such a manner that a rotation is inhibited from being carried out around the rotational symmetric axis z 1 . The additional member  6  is engaged with the recess portion  18  while the additional member  6  is maintained to be fitted in the recess portion  18  by the biasing force of the elastic member  32 . In the holding state, thus, the additional member  6  is fixed to the head body  4 . In the sectional views showing the holding state in  FIG. 6  and the like, a small clearance is drawn between the recess portion  18  and the additional member  6 . This is drawn for easy understanding of the drawings and the clearance is not actually present. 
         [0059]      FIG. 8  is a view for explaining a step of assembling a holding mechanism  28 . At this step, the bar-shaped member  30  which is integrated with the engaging portion  42  and the elastic member  32  are disposed on the inside (the hollow portion) of the head  2 . On the other hand, the additional member  6  is disposed in the recess portion  18 . Next, the bar-shaped member  30  is inserted into the elastic member  32 . The drawing on an upper side of  FIG. 8  shows this state. Then, the male screw portion  36  of the bar-shaped member  30  is inserted into the through hole  40  so that the male screw portion  36  is screwed into the female screw hole  34 . By the screwing, a state shown in the drawing on a lower side of  FIG. 8  is brought so that the holding mechanism  28  is completely assembled. 
         [0060]      FIG. 9  is a sectional view showing a first variant of the embodiment in  FIG. 6 . A head according to the variant is the same as the head  2  except for an additional member  49 . In the variant, the additional member  49  has an additional member body  50 , a separate member  26  and an elastic member  56 . The elastic member  56  is disposed in at least a part between a side surface  52  of the additional member body  50  and a wall surface  54  of the recess portion  18 . In the holding state, the elastic member  56  abuts on the wall surface  54 . 
         [0061]    A microvibration might be generated in the additional member body  50  due to an impact in hitting. In some cases, the microvibration causes a durability of the additional member  49  to be deteriorated or a noise to be generated. The noise is generated when the additional member body  50  collides with the head body  4 . The elastic member  56  can absorb the microvibration of the additional member body  50 . By the elastic member  56 , it is possible to enhance the durability of the additional member body  50 . By the elastic member  56 , it is possible to effectively prevent the noise from being generated. 
         [0062]    Examples of a material of the elastic member  56  include a vulcanized rubber and a resin. Examples of the resin include a thermosetting resin and a thermoplastic resin. As an example of the resin, an elastomer containing a soft segment and a hard segment is taken. The elastic member  56  may be attached to the additional member body  50  or the recess portion  18 . The elastic member  56  may be provided between a bottom face  46  of the recess portion  18  and an internal surface  51  of the additional member  49 . The elastic member  56  can be attached with an adhesive agent, for example. 
         [0063]      FIG. 10  is a sectional view showing an assembling step according to a second variant of the embodiment in  FIG. 6 . In the second variant, an additional member  60  and a bar-shaped member  62  are formed integrally. In the second variant, the bar-shaped member  62  and an engaging portion  64  are not formed integrally. Except for these respects, the second variant is the same as the head  2  described above. 
         [0064]    At the assembling step according to the second variant, first of all, an elastic member  32  and an engaging portion  64  are disposed on an inside (a hollow portion) of a head, and an additional member  60  integrated with the bar-shaped member  62  is disposed on an outside of the head (see an upper stage of  FIG. 10 ). Next, the bar-shaped member  62  is inserted into a through hole  40  and the bar-shaped member  62  protruded to the inside of the head is inserted through the elastic member  32  (see a middle stage of  FIG. 10 ). Finally, the engaging portion  64  is attached to an end of the bar-shaped member  62  (see a lower stage of  FIG. 10 ). Means for bonding the engaging portion  64  to the bar-shaped member  62  is not restricted but bonding, welding and screwing can be taken as an example. 
         [0065]      FIG. 11  is a perspective view showing an additional member  66  according to a third variant. A hanging portion  72  for causing the external force F 1  to easily act is provided on an external surface  70  of the additional member  66 . A jig (not shown) having a hook or the like on an end is hung on the hanging portion  72  so that the external force F 1  can easily be applied. The hanging portion  72  is provided in a recess portion  74  and is not protruded from the external surface  70 . 
         [0066]      FIG. 12  is a perspective view showing a head  76  according to another embodiment.  FIG. 12  is a perspective view showing the head  76  seen from a back side. The head  76  includes a head body  78  and an additional member  80 . 
         [0067]    The head body  78  has a face portion which is not shown, a sole portion which is not shown, a crown portion  82 , a side portion  84  and a hosel portion  86 . An inner part of the head body  78  is hollow, which is not shown. 
         [0068]      FIG. 13  is a sectional view showing the head  76  set in a longitudinal direction of the additional member  80 .  FIG. 13  shows only the vicinity of the additional member  80 . A recess portion  88  is provided on the side portion  84 . The additional member  80  can be fitted in the recess portion  88 . The whole additional member  80  is fitted in the recess portion  88 . In the head  76 , the whole additional member  80  is accommodated in the recess portion  88 . 
         [0069]    The recess portion  88  has a planar shape of I. The additional member  80  has a planar shape of I. The planar shape of the recess portion  88  corresponds to that of the additional member  80 . 
         [0070]    In the additional member  80 , a contour shape obtained by a projection onto a plane has a rotational symmetry. In the additional member  80 , the contour shape obtained by the projection onto the plane has a rotational symmetric axis z 1 . The details of the rotational symmetry and the rotational symmetric axis z 1  will be described below. 
         [0071]    In the recess portion  88 , a contour shape obtained by a projection onto a plane has a rotational symmetry. In the recess portion  88 , the contour shape obtained by the projection onto the plane has a rotational symmetric axis z 2 . The details of the rotational symmetry and the rotational symmetric axis z 2  will be described below. 
         [0072]    In the embodiment shown in  FIG. 6 , the bottom face  46  of the recess portion  18  is a plane. On the other hand, a bottom face  90  of the recess portion  88  is a curved surface. In the embodiment shown in  FIG. 6 , an internal surface  22  of the additional member  6  is a plane. On the other hand, an internal surface  92  of the additional member  80  is a curved surface. 
         [0073]    The additional member  80  has a body  94  and a separate member  96 . The separate member  96  is fitted in a recess portion provided on the body  94 . A material of the body  94  has a different specific gravity from that of a material of the separate member  96 . Thus, the additional member  80  is formed by at least two materials having different specific gravities from each other. A center of gravity of the additional member  80  is not present on the rotational symmetric axis z 1 . 
         [0074]    The head  76  includes a holding mechanism  98  for holding the additional member  80 . The holding mechanism  98  has a bar-shaped member  100  and an elastic member  102 . In the present embodiment, the elastic member  102  is a coil spring. The coil spring is a compression spring. 
         [0075]    A structure of the holding mechanism  98  is the same as that of the holding mechanism  28 . A mechanism for carrying out a mutual transition of a holding state and a releasing state is the same as that in the head  2 . 
         [0076]      FIG. 14  is a sectional view showing a head according to a further embodiment. In the sectional view, the vicinity of an additional member  104  is shown. In the embodiment, an elastic member is not used. In the present embodiment, the additional member  104  and a head body  106  are fixed to each other through a screw member  108 . A through hole  110  is provided on the additional member  104 . The through hole  110  has a large diameter portion  112  and a small diameter portion  114 . A step surface  115  is present on a boundary between the large diameter portion  112  and the small diameter portion  114 . The screw member  108  has a head portion  116  and a male screw portion  118 . The head body  106  has a recess portion  120 . A female screw hole  122  is provided in a bottom face portion of the recess portion  120 . The head portion  116  is accommodated in the large diameter portion  112  of the through hole  110 . In the holding state, the head portion  116  is not protruded from an external surface  117  of the additional member  104 . 
         [0077]      FIG. 14  is a view showing the holding state. In the holding state, the head portion  116  of the screw member  108  abuts on the step surface  115 . An inside diameter of the small diameter portion  114  is smaller than an outside diameter of the head portion  116 . The head portion  116  is not inserted into the small diameter portion  114 . On the other hand, an outside diameter of the male screw portion  118  is smaller than the inside diameter of the small diameter portion  114 . In the holding state, the male screw portion  118  is screwed into the female screw hole  122 . By the screwing, the additional member  104  is fixed to the head body  106 . In order to bring the releasing state, the male screw portion  118  and the female screw hole  122  are unscrewed to pull the additional member  104  out of the recess portion  120 . In the releasing state, the additional member  104  can be rotated around a rotational symmetric axis z 1 . In a stage in which the male screw portion  118  and the female screw hole  122  are not perfectly unscrewed, the releasing state is implemented. In order to implement the releasing state with the male screw portion  118  and the female screw hole  122  maintained to be screwed, a length of the male screw portion  118 , a length of the female screw hole  122  and a thickness of the additional member  104  are regulated. In the present invention, such a configuration may be employed. 
         [0078]    In each of the embodiments described above, the contour shape of the additional member which is obtained by a projection onto a plane has the rotational symmetric axis z 1 .  FIG. 15  shows an example of the contour shape obtained by the projection onto the plane.  FIG. 15(   a ) shows a contour shape K 1  obtained by projecting the additional member  6  onto a plane P 1 . The plane P 1  is shown in a one-dotted chain line in  FIGS. 6 and 13 . The rotational symmetric axis z 1  is a rotational symmetric axis for the contour shape obtained by the projection onto the plane P 1 . The plane P 1  is set to abut on the external surface of the additional member on at least one point. The projection onto the plane P 1  is carried out in a perpendicular direction to the plane P 1 . It is preferable to set the plane P 1  in order to obtain a projected image having the rotational symmetric axis. The rotational symmetric axis z 1  passes through a center of gravity of the contour shape K 1  and is perpendicular to the plane P 1 . In the case in which the contour shape has a plurality of rotational symmetric axes, one of them can be employed as the rotational symmetric axis z 1  in the present invention. 
         [0079]      FIG. 15(   b ) shows a contour shape K 2  obtained by projecting the additional member  80  onto the plane P 1 .  FIG. 15(   c ) shows a contour shape K 3  obtained by projecting the additional member according to another example onto the plane P 1 .  FIG. 15(   d ) shows a contour shape K 4  obtained by projecting the additional member according to a further example onto the plane P 1 .  FIG. 15(   e ) is a perspective view showing an example of an additional member  124  having the contour shape K 4 . 
         [0080]    In the present invention, it is sufficient that the contour shape obtained by the projection onto the plane P 1  has a rotational symmetry and the additional member itself does not need to have the rotational symmetry. In the present invention, the additional member itself does not need to have the rotational symmetric axis. 
         [0081]    As a matter of course, the additional member itself may have the rotational symmetry as in the additional member  6  or  80 . 
         [0082]    In the additional member  6  according to the embodiment, the external surface  20  is a plane and the internal surface  22  is also a plane, and the additional member  6  has a constant thickness. The additional member  6  itself has the rotational symmetry. In the additional member  6  according to the embodiment, the rotational symmetric axis z 1  of the contour shape is coincident with a rotational symmetric axis z 3  of the additional member  6 . In other words, the additional member  6  has the rotational symmetric axis z 3  which is coincident with the rotational symmetric axis z 1  of the contour shape. The rotational symmetric axis z 3  is owned by the additional member  6  itself. The additional member  6  has a plurality of rotational symmetric axes and one of them serves as the rotational symmetric axis z 3 . 
         [0083]    In the additional member  80 , the rotational symmetric axis z 1  of the contour shape is coincident with the rotational symmetric axis z 3  of the additional member  80 . 
         [0084]    The additional member according to the present invention is not restricted to the case in which the additional member has the rotational symmetry as in the additional member  6 . For example, it is also possible to employ an additional member A 1  (not shown) in which the contour shape obtained by the projection onto the plane P 1  is the same as that of the additional member  6  and a thickness is not constant. A rotational symmetric axis z 1  of the additional member A 1  is the same as the rotational symmetric axis z 1  of the additional member  6 . Examples of the additional member A 1  include an additional member in which the first extended portion  6   a,  the second extended portion  6   b,  the third extended portion  6   c  and the fourth extended portion  6   d  have different thicknesses from each other. In case of the additional member in which the extended portions  6   a  to  6   d  have the different thicknesses from each other, it is possible to shift a position of a center of gravity of the additional member from the rotational symmetric axis z 1  without providing the separate member  26 . 
         [0085]    In the embodiment, the contour shape obtained by projecting the recess portion  18  onto the plane P 1  is substantially the same as the contour shape obtained by projecting the additional member  6  onto the plane P 1 . The rotational symmetric axis z 2  serves as a rotational symmetric axis of the contour shape obtained by projecting the recess portion  18  onto the plane P 1 . 
         [0086]    In the present invention, the contour shape of the recess portion which is obtained by the projection onto the plane does not need to have the rotational symmetry. In a state in which the additional member is fitted in the recess portion, it is sufficient that a rotation can be inhibited from being carried out around the rotational symmetric axis z 1  of the additional member. In order to inhibit the rotation more reliably, it is preferable that the contour shape of the recess portion should have the rotational symmetric axis z 2 . In order to reliably inhibit the rotation, it is more preferable that the contour shape of the recess portion which is obtained by the projection onto the plane P 1  should be the same as the contour shape of the additional member which is obtained by the projection onto the plane P 1 . In order to reliably inhibit the rotation, it is preferable that the whole side surface of the additional member should be close to the wall surface of the recess portion with substantively no clearance in the holding state. 
         [0087]    As a matter of course, the recess portion (the recess portion itself) may have a rotational symmetric axis z 4 . The recess portion  18  of the head body  4  has a rotational symmetry. In the recess portion  18 , the rotational symmetric axis z 2  of the contour shape obtained by the projection is coincident with the rotational symmetric axis z 4  of the recess portion  18 . In other words, the recess portion  18  has the rotational symmetric axis z 4  which is coincident with the rotational symmetric axis z 2  of the contour shape. The rotational symmetric axis z 4  means a symmetric axis of the recess portion  18  itself. The recess portion  18  has a plurality of rotational symmetric axes, and one of the rotational symmetric axes serves as the rotational symmetric axis z 4 . 
         [0088]    The case in which a shape obtained with a rotation of (360/N) degrees around a certain axis is coincident with an original shape indicates an “N-fold rotational symmetry” with respect to the same axis. Every shape is one-fold rotational symmetric. For this reason, the case in which N is one is not regarded to have the rotational symmetry. When N is a natural number of two or more, it is regarded to have the rotational symmetry. The contour shape K 1  shown in  FIG. 15  is four-fold rotational symmetric. The contour shape K 2  shown in  FIG. 15  is two-fold rotational symmetric. The contour shape K 3  shown in  FIG. 15  is three-fold rotational symmetric. The contour shape K 4  shown in  FIG. 15  is four-fold rotational symmetric. 
         [0089]    In the case in which the contour shape is the N-fold rotational symmetric, the additional member brought into the holding state can take N types of phases. In this case, accordingly, it is possible to adjust the position of the center of gravity of the head in N ways. In order to increase the degree of freedom for the adjustment of the position of the center of gravity, N is preferably equal to or greater than three and is more preferably equal to or greater than four in the contour shape of the additional member. In the case in which the shape of the additional member is excessively complex, a manufacturing cost of the additional member is excessively increased or a work for fitting the additional member in the recess portion is complicated when a transition from the releasing state to the holding state is carried out. From this viewpoint, N is preferably equal to or smaller than 20, is more preferably equal to or smaller than 12 and is further preferably equal to or smaller than eight. 
         [0090]    In order to obtain a head which is not excessively light, a specific gravity H 1  of the head body is preferably equal to or greater than two, is more preferably equal to or greater than 2.5 and is further preferably equal to or greater than three. In order to increase a weight which can be distributed to the additional member, thereby enhancing the degree of freedom for a movement of the center of gravity, the specific gravity H 1  of the head body is preferably equal to or smaller than ten, is more preferably equal to or smaller than eight and is further preferably equal to or smaller than six. 
         [0091]    In order to increase a strength of the additional member, a specific gravity H 2  of the body of the additional member is preferably equal to or greater than 0.5, is more preferably equal to or greater than 0.8 and is further preferably equal to or greater than 1.0. In order to prevent the weight of the head from being increased excessively, the specific gravity H 2  is preferably equal to or smaller than five, is more preferably equal to or smaller than four and is further preferably equal to or smaller than three. 
         [0092]    It is preferable that the specific gravity H 2  should be smaller than the specific gravity H 1 . By setting H 2 &lt;H 1 , it is possible to reduce the weight of the body of the additional member, thereby distributing the extra weight to other portions. 
         [0093]    In order to enhance the effect of adjusting the position of the center of gravity, a specific gravity H 3  of a separate member of the additional member is preferably equal to or greater than five, is more preferably equal to or greater than six and is further preferably equal to or greater than seven. In order to prevent the weight of the head from being increased excessively, the specific gravity H 3  is preferably equal to or smaller than 20, is more preferably equal to or smaller than 18 and is further preferably equal to or smaller than 16. 
         [0094]    It is preferable that the specific gravity H 3  should be greater than the specific gravity H 1 . By setting H 1 &lt;H 3 , it is possible to enhance the effect of adjusting the position of the center of gravity through the additional member. 
         [0095]    In order to enhance the effect of adjusting the position of the center of gravity, (H 3 /H 1 ) is preferably equal to or greater than 1.5, is more preferably equal to or greater than two and is further preferably equal to or greater than 2.5. In order to prevent an excessive reduction in the weight of the head body or to prevent an excessive increase in the weight of the additional member, (H 3 /H 1 ) is preferably equal to or smaller than seven, is more preferably equal to or smaller than six and is further preferably equal to or smaller than five. 
         [0096]    If (H 3 /H 2 ) is too small, the additional member is excessively heavy or the effect of adjusting the position of the center of gravity is reduced. From this viewpoint, (H 3 /H 2 ) is preferably equal to or greater than three, is more preferably equal to or greater than four and is further preferably equal to or greater than five. If (H 3 /H 2 ) is too great, a weight of the body of the additional member is excessively reduced so that the strength of the additional member is apt to be reduced or the weight of the additional member is apt to be increased excessively. In this respect, (H 3 /H 2 ) is preferably equal to or smaller than  18 , is more preferably equal to or smaller than 14 and is further preferably equal to or smaller than 12. 
         [0097]    If (H 1 /H 2 ) is too small, the weight of the additional member is increased excessively or the weight of the head body is apt to be reduced excessively. From this viewpoint, (H 1 /H 2 ) is preferably equal to or greater than one, is more preferably equal to or greater than 1.2 and is further preferably equal to or greater than 1.5. In order to obtain a head which is not excessively light, (H 1 /H 2 ) is preferably equal to or smaller than eight, is more preferably equal to or smaller than six and is further preferably equal to or smaller than four. 
         [0098]    In order to enhance the effect of adjusting the position of the center of gravity, a distance Dz (the shortest distance) between the rotational symmetric axis z 1  and the center of gravity of the additional member is preferably equal to or greater than 5 mm, is more preferably equal to or greater than 8 mm and is further preferably equal to or greater than 10 mm. In order to take a shape of the head with which a golf player feels uncomfortable with difficulty, the distance Dz is preferably equal to or smaller than 80 mm, is more preferably equal to or smaller than 60 mm and is further preferably equal to or smaller than 50 mm. 
         [0099]    For a material of the head body, it is possible to use the same material as a general golf club head. Examples of the material include at least one selected from titanium, a titanium alloy, stainless steel, an aluminum alloy, a magnesium alloy and CFRP (carbon fiber reinforced plastic). In respect of a specific strength, the titanium alloy is suitable. 
         [0100]    A method of manufacturing the head body is not particularly restricted but casting, forging and press forming can be taken as an example. Examples of a structure of the head body include a two-piece structure obtained by combining two members which are integrally formed respectively, a three-piece structure obtained by combining three members which are integrally formed respectively, a fourth-piece structure obtained by combining four members which are integrally formed respectively, and the like. Examples of the head body having the two-piece structure include a head body constituted by a member having a face opened and a face member, a head body constituted by a member having a crown opened and a crown member, and the like. Examples of the head body having the three-piece structure include a head body constituted by a member having a face and a crown opened, a face member and a crown member. Examples of the head body having the four-piece structure include a head body constituted by a face member, a crown member, a sole member and a hosel member. 
         [0101]    Examples of a material of the body of the additional member include a metal and a resin. In order to set the specific gravity H 2  into a preferable range, examples of a preferable metal include a titanium alloy, an aluminum alloy and a magnesium alloy. Examples of the resin include engineering plastic, superengineering plastic and CFRP (carbon fiber reinforced plastic). Examples of the engineering plastic include polycarbonate (PC), polyamide (PA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyacetal (POM), polyphenylene ether (PPE), and the like. Examples of the superengineering plastic include polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyether nitrile (PEN), polysulfone (PSE), polyether sulfone (PES), polyallylate (PAR), polyamide-imide (PAI), polyether-imide (PEI), thermoplastic polyimide (PI) and the like. 
         [0102]    Examples of the material of the separate member in the additional member include a metal. In order to set the specific gravity H 3  into a preferable range, examples of the material of the separate member include tungsten, a tungsten alloy, stainless steel, copper, a copper alloy, lead, a lead alloy and the like. Examples of the tungsten alloy include a W—Ni alloy (a tungsten nickel alloy) and a W—Cu alloy (a tungsten copper alloy). 
       EXAMPLES 
       [0103]    Although the effects of the present invention will be apparent from examples, the present invention should not be construed to be restrictive based on description of the examples. 
       Example 1 
       [0104]    The same head as the head  2  was fabricated. A head body was set to have a two-piece structure constituted by a member having a face opened (which will be hereinafter referred to as a face opening member) and a face member. A material of the face opening member was set to be Ti-6Al-4V (a specific gravity of 4.42). A material of the face member was set to be Ti-6Al-4V. The face opening member was integrally formed through casting. By the casting, a recess portion was formed on a sole portion. A through hole positioned on a center of the recess portion was formed through an NC processing. 
         [0105]    A material of a body of an additional member was set to be an aluminum alloy (a specific gravity of 2.8). A recess portion for accommodating a separate member was provided on the body of the additional member through the NC processing. A female screw hole was provided on the body of the additional member through cutting. A separate member formed of a tungsten alloy (a specific gravity of 16) was fitted in the recess portion. The body of the additional member and the separate member were bonded to each other with an adhesive agent. A distance L 1  (see  FIG. 5 ) from the rotational symmetric axis z 1  to an end face of the first extended portion  6   a  was set to be 35 mm. A distance L 2  (not shown) from the rotational symmetric axis z 1  to an end face of the second extended portion  6   b  was also set to be 35 mm. A distance L 3  (not shown) from the rotational symmetric axis z 1  to an end face of the third extended portion  6   c  was also set to be 35 mm. A distance L 4  (not shown) from the rotational symmetric axis z 1  to an end face of the fourth extended portion  6   d  was also set to be 35 mm. A thickness of the additional member was set to be constant, that is, 5 mm. A material of an integral member constituted by a bar-shaped member and an engaging portion was set to be an aluminum alloy (a specific gravity of 2.8). An outside diameter of the bar-shaped member was set to be 5 mm. A length of the bar-shaped member was set to be 15 mm. A length of the engaging portion in an axial direction of the bar-shaped member was set to be 2 mm. An outside diameter of the engaging portion was set to be 15 mm. For a material of a coil spring, spring steel SUP9 was used. In accordance with the procedure described with reference to  FIG. 8 , the additional member, the bar-shaped member, the coil spring and the engaging portion were attached to the face opening member. Then, the face opening member and the face member were bonded through plasma welding so that the head was obtained. In the present example, four types of head center-of-gravity positions were implemented in the holding state. In the present example, it was possible to move the center of gravity of the head without removing the rotating member. 
         [0106]    The above description is only illustrative and various changes can be made without departing from the scope of the present invention. 
         [0107]    The present invention can be applied to all of golf club heads, for example, a golf club head of a wood type, a golf club head of an iron type, a patter head and the like.