Abstract:
A golf club head is disclosed that comprises a body having a striking face and a sole, wherein a recess is formed in the sole. An insert is located within the sole recess, the insert including a core and an intermediate layer that at least partially separates the core from the recess wall. The intermediate layer has a hardness and a modulus of elasticity that are less than that of the core, such that when the golf club head is used to strike a golf ball, the resulting vibrations are dissipated by compression of the intermediate layer and movement of the core with respect to the intermediate layer.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to the game of golf and, more particularly, to golf club heads. 
     Modern golf clubs have typically been classified as either woods, irons or putters. The term “wood” is an historical term that is still commonly used, even for golf clubs that are constructed of steel, titanium, fiberglass and other more exotic materials, to name a few. The term “iron” is also an historical term that is still commonly used, even though those clubs are not typically constructed of iron, but are rather constructed of many of the same materials used to construct “woods.” 
     Many advancements have been achieved, particularly over the past couple of decades, to make it easier to hit longer and straighter shots with woods and irons. In general, golf clubs are now designed to be more forgiving, so that shots that are struck less than perfectly will still have fairly consistent distance and directional control. Moreover, club heads now commonly are constructed of combinations of materials, to attempt to optimize the ball flight desired by a particular type of player. 
     One particular improvement that relates to irons is the use of perimeter weighting, whereby a disproportionate amount of the total weight of a club head is positioned behind and proximate the perimeter of the club head&#39;s striking face, thereby creating a cavity immediately behind the striking face. The cavity is formed by the club face and the weight that is placed around and behind the club face. This type of club is typically referred to a “cavity back” iron. By moving the weight away from the center of gravity (CG) of the club head, the club is made to be more forgiving on off-center hits, resulting in more consistent distance and directional control. Further, perimeter weighting generally increases the moment of inertia about the club&#39;s center of gravity, resulting in less twisting due to off-center hits, and more accurate shots. 
     Another improvement is the use of lighter and stronger materials, which enables club designers to move the CG to an optimal location on a wood or iron. Such a movement can make the club either easier to hook or to fade, if the movement is made either closer to or farther from the hosel. Similarly, if the CG is moved higher or lower with respect to the club face, the golf ball launch conditions can be altered. For instance, lowering the CG generally makes it easier to the get the ball airborne for either an iron or a wood. Conversely, raising the CG promotes a more boring ball flight that generally leaves the club face at a lower launch angle. 
     Generally, it has been shown that it can be advantageous for players with higher handicaps to use clubs with a lower CG. This is especially true for long irons, such as for example a 3-iron. Club designers have responded to this prospective advantage by lowering the CG of both woods and irons for clubs intended for higher handicap players. The most common way that this has been accomplished for irons is to move as much weight as possible to the area proximate the sole of the club. This results is a concentration of weight proximate the sole. Often, for these types of irons, the transition from the cavity to the weight on the sole is abrupt, compared to traditional irons having a smoother transition. When viewing a cross-section of the lower portion of the club face, a dramatic change in the thickness of the face nearer the sole often is apparent in such sole-weighted club beads. 
     While it is recognized that the lower CG of the improved clubs can be beneficial, such a lowering can have negative side effects. First, the concentrated mass proximate the sole can increase the stiffness of the club head. This can cause a noticeable change in the club&#39;s feel. Feel is a term that is generally used by skilled practitioners to denote a subjective expression of the way a club feels to one&#39;s hands when striking a ball, or the way it sounds. Feel is generally perceived as audible or tactile feedback to the golfer. Different sensations due to striking the ball in different locations on the club face may make a club less desirable to a potential user. 
     Second, the weight concentration proximate the sole can lead to different levels of flex at different points on the club face. The area of the face proximate the thickest portion of the sole is likely to flex less than the area proximate the thinner areas of the striking face. Such a change in flex can adversely affect performance. 
     Third, the weight concentration can lead to excess vibration, which can adversely affect the feel of the golf club, including the sound made by the club. 
     It should be appreciated from the foregoing description that there is a need for an improved golf club head that creates a more consistent flex when striking the ball, improves the club&#39;s feel, and reduces vibration. The present invention satisfies this need and provides further related advantages. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solution to counteract the negative side affects described above, by allowing club designers to design a club with an optimal center of gravity, while at the same time lowering the stiffness proximate the sole, creating more consistent flex while striking the ball, improving the feel of the club, and reducing vibration. 
     Generally, the present invention can be practiced using a variety of common club head shapes that are known in the art. Preferably, the club head comprises a unitary body that has a striking face and a sole. A recess is preferably formed in the sole that is adapted for receiving an insert. The preferred insert comprises a core and an intermediate layer. The intermediate layer generally is formed from a material that has a hardness and a modulus of elasticity that are lower than that of the core. The intermediate layer is generally disposed so that it partially encapsulates the core or fills interstices within the core. Three embodiments of the invention are shown and described below. 
     According to the first preferred embodiment of the invention, a set of cells are embedded proximate a sole portion of a preferred club head. The preferred club head comprises a body that has perimeter weighting and a cavity back. The cavity back may be either open or closed, such as for example in a hollow club head. The body is substantially similar to many cavity back clubs that are known in the art. The perimeter weighting of the preferred body forms a sole bar proximate the sole. The sole bar has an elongated slot that is formed or is cut therethrough, the slot extending between the toe and the heel of the body. Proximate the slot are a plurality of a apertures that are formed so as to receive a corresponding plurality of cells. The number of apertures may vary. 
     The cells each comprise a pin that is preferably encased in an elastomeric sleeve. The preferred cells, the apertures, and the preferred pins and sleeves are generally aligned so that their longitudinal axes are parallel with the striking face of the golf club head. Further, the longitudinal axes are preferably aligned generally parallel with the loft angle of a particular club. 
     During manufacture, the preferred cells are preferably inserted through the elongated slot, and sealed from the sole and held in place by a plug that is inserted into the slot so as to be flush with the sole upon completion of manufacture. The plug is held in place by conventional means known in the art, some of which are described below in the Detailed Description. 
     According to a second embodiment of the invention, a cartridge is used to provide the advantages described above. The preferred cartridge comprises a metal substrate having a plurality of interstices spaced therein. The interstices are preferably filled with a polymeric material. 
     According to a third embodiment of the invention, a cartridge is used to provide the advantages described above. The preferred cartridge comprises a metal substrate having a plurality of interstices spaced therein. A polymeric sleeve is preferably folded over a portion of the metal substrate. The preferred polymeric sleeve has nubs on an outer surface where contact is made with the club head body. 
     It is an object of the present invention to provide a golf club head that reduces club head stiffness. 
     It is a further object of the present invention to provide a golf club head that results in a more uniform face deflection in the hitting area. 
     It is a further object of the present invention to provide a golf club head that improves the feel of a golf club. 
     It is a further object of the present invention to provide a golf club head that absorbs energy. 
     It is a further object of the present invention to provide a golf club head that improves the weight distribution of a golf club. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a golf club head of the preferred embodiment, having a sole, a striking face, a heel and an insert assembly. 
     FIG. 2 is an exploded view of a rear cavity and an insert assembly that are part of the golf club head of FIG.  1 . 
     FIG. 3 is an exploded view of a cell that can be used with the golf club head of FIG.  1 . 
     FIG. 4 is a bottom view of the golf club head of FIG. 1, showing the sole and a slot formed within the sole. 
     FIG. 4A is a cross-sectional view of the golf club head of FIG. 4, viewed along line A—A, showing the preferred insert assembly and the rear cavity. 
     FIG. 5 is a front view of the golf club head of FIG. 1, showing its striking face. 
     FIG. 5A is a cross-sectional view of the golf club head of FIG. 5, viewed along line A—A, depicting the slot in the sole and one of a plurality of preferred apertures formed therein, and further depicting a side view of the preferred cavity. 
     FIG. 5B is an enlarged view of the circled portion of FIG. 5A, depicting the nearly assembled club head with the insert assembly in place and a plug that is ready to be ground flush with the sole. 
     FIG. 6 is a rear view of the cavity of the golf club head of FIG. 1, showing an exploded view of a preferred badge that is not yet attached to the cavity. 
     FIG. 7 is a front view of a second preferred embodiment of a golf club head in accordance with the invention, showing the club head&#39;s striking face. The club head body shown in FIG. 7 is substantially similar to the club head body shown in FIGS. 1-6, except for the dimensions of the slot formed therein. 
     FIG. 7A is a cross-sectional view of the golf club head of FIG. 7, viewed along line A—A, depicting the slot in the sole formed therein, and further depicting a side view of the preferred cavity. 
     FIG. 7B is an enlarged view of the circled portion of FIG. 7A, depicting the assembled club head with the cartridge in place. 
     FIG. 8 is a front view of a third preferred embodiment of a golf club head in accordance with the invention, showing the club head&#39;s striking face. The club head body shown in FIG. 8 is substantially similar to the club head body shown in FIGS. 1-6, except for the dimensions of the slot formed therein. 
     FIG. 8A is a cross-sectional view of the golf club head of FIG. 8, viewed along line A—A, depicting the slot in the sole formed therein, and further depicting a side view of the preferred cavity. 
     FIG. 8B is an enlarged view of the circled portion of FIG. 8A, depicting the assembled club head with the cartridge in place. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference now to the exemplary drawings, and particularly to FIGS. 1 and 5, there is shown a preferred golf club head  10  in accordance with the present invention. The club head  10  is similar to many cavity back club heads that are known in the art. The club head  10  includes a body  11  having a front striking face  15  that is bounded by a striking face perimeter  18 . The perimeter is proximate a heel  12 , a toe  13 , a sole  14 , a hosel  17  and a top line  16 . The striking face  15  is the portion of the body  11  that is used to make contact with a golf ball (not shown). The hosel  17  allows the club head  10  to be connected to a shaft and a grip (not shown), to form a complete golf club, as is known in the art. 
     The body  11  also has a rear cavity  20  that is bounded by a cavity perimeter  19 , as shown in FIG.  2 . As is typical of many cavity back irons, the preferred body  11  has a cavity wall  21  that forms the back side of the striking face  15  and that is substantially parallel to the striking face  15 . The cavity perimeter  19  is proximate to, and surrounds, the cavity wall  21 . The cavity perimeter  19  has a cavity rim  22  that extends substantially rearwardly from the cavity wall  21  and the striking face  15 , as shown is FIG.  5 A. The cavity rim  22  surrounds the cavity  20 , as shown in FIG.  2 . Although a cavity back iron is shown and described, the invention described herein may apply to other irons having a sole bar, such as hollow-headed irons. 
     The construction of the body  11  is such that a substantial amount of the weight is concentrated proximate the cavity perimeter  19 , hence a common description is “perimeter weighted,” or “cavity back.” The preferred body  11  has perimeter weighting  25  that comprises a mass of material that extends rearwardly of the striking face perimeter  18 . The preferred perimeter weighting  25  may extend proximate the entire perimeter  18 , or a portion thereof, dependent on desired weight distribution characteristics. The perimeter weighting  25  includes a sole bar  26 , which is a concentrated mass that is located proximate the sole  14  so as to provide the desired weight distribution characteristics. 
     As is known in the art, the perimeter weighting  25  may take various shapes as it wraps from the striking face  15  to the cavity wall  21 . FIGS. 2,  5 A and  5 B show the preferred perimeter weighting  25  configuration, with a cavity transition  23  between the cavity rim  22  and the sole  14 . The transition  23  may be in the form of a radius or a series of degradations. 
     The body  11  has a raised cavity center weight  27  that protrudes rearwardly from the cavity wall  21  and that is bordered by the cavity perimeter  19  on two sides and by cavity step downs  28 ,  29 . Alternatively, the cavity wall  21  could be substantially flat or have other shapes to create different performance characteristics and different weight distribution. 
     The body  11  preferably is formed of a cast stainless steel. This material is preferred because of its ductility, its relative softness that contributes to good feel, its resistance to corrosion, its strength, and its ability to be investment cast. A variety of stainless steel products and other similar known materials alternatively could be used. 
     As shown in FIGS. 1,  2  and  4 , the body  11  has a slot  60  formed proximate the sole  14 . The slot  60  preferably extends longitudinally between the heel  12  and the toe  13 . The slot  60  is formed within the sole bar  26 , and it is defined by a slot wall  61  running on all sides of the slot  60  and a shoulder  68 . The slot  60  has a toe end  62  and a heel end  63 , as shown in FIG.  4 . 
     Preferably, a plurality of cylindrical apertures  64  are formed proximate the slot  60 , as shown in FIGS. 4A and 5A. The apertures  64  each have a proximal end  67  and a distal end  66 . The proximal end  67  is located proximate the slot shoulder  68  and the distal end  66  is located nearer to the cavity rim  22 . Preferably, the distal end  66  of each aperture does not enter the cavity  20 . Subject to manufacturing constraints, a further embodiment would have apertures extending into the cavity  20 , entering the cavity proximate the cavity rim  21 . The apertures  64  are preferably cylindrical in shape, and form conical sections at their distal ends  66 , as a result of the use of drill bits in manufacture. Other similar shapes could be used. Each aperture  64  is defined by an aperture wall  65 . 
     Preferably, the axis of each aperture  64  is parallel to the striking face  15  and substantially perpendicular to a plane defined by the sole  14 . 
     The slot  60  and the apertures  64  may be formed by means known in the art. In the preferred embodiment, a slot  60  and a plurality of apertures  64  are cast into the body  11  and then machined and drilled to appropriate tolerances. The slot  60  and apertures  64  are sized and configured to receive an insert assembly  30 , as shown in FIGS. 1 and 2. The preferred insert assembly  30  comprises a plug  31  and a plurality of cells  40  that are sized and configured to fit within the slot  60  and the apertures  64 . 
     A preferred cell  40  is shown in FIG.  3 . Each cell  40  may include a sleeve  41  and a pin  42 , as separate units. When placed in an aperture, each sleeve  41  partially or totally encases a corresponding pin  42 . The sleeve  41  may form an air pocket  49  at one or both ends. The sleeve  41  has a top  44 , a bottom  45 , an inner wall  47 , an outer wall  48 , and a shoulder  43 . The interface between the outer wall  48  and the bottom  45  may be flared outwardly to assist in manufacturing. The shoulder  43  and inner wall  47  define a void  46  where the pin  42  may be inserted upon final assembly. The dimensions of the cell  40 , including the pin  42  and the sleeve  41 , can vary for different irons within a set of clubs, due to the different dimensions of the respective soles and sole bars for those different irons. 
     The preferred sleeve  41  may be constructed using an elastomer, including thermoplastic materials such as urethane. The sleeve may be formed of a variety of materials known in the art, so long as the chosen material has a hardness and modulus of elasticity that are lower than that of the pin  42 , and so long as it is easy to manufacture. For example, the preferred material, urethane, is sufficiently elastic and can be injection molded, so that it is readily manufacturable. 
     The preferred pin  42  may be constructed of stainless steel or a variety of similar materials that are known in the art, so long as the chosen material is sufficiently dense and has a relatively high modulus of elasticity. Exemplary materials include steel, copper, bronze, tungsten and nickel, to name a few. 
     The assembled cell  40  is inserted into a corresponding aperture  64  by means known in the art. When fully inserted, the sleeve  41  generally prevents the pin  42  from contacting the body  11 , so that there is minimal or no contact between the pin  42  and the body  11 . The preferred body  11  has five apertures  64  and five cells  40 , although that number may be varied based on the damping, stiffness, feel and weight distribution characteristics that are desired. 
     The preferred cells  40  are held in place in the apertures by the plug  31 . The preferred plug  31  has a substantially flat inner wall  34 , a circumferential side wall  33  that extends around the plug  31 , and a generally curved sole portion  32 . When assembled, the inner wall  34  seats proximate the shoulder  68 , and it frictionally holds the cells  40  in place. The plug side wall  33  when assembled is proximate the slot wall  61 , and the plug sole  32  is proximate the sole  14 . 
     The plug  31  preferably includes a set of ridges  36 , one on each side, as particularly shown in FIG.  5 B. The slot  60  preferably has a recess  35  that runs longitudinally between the toe end  62  and heel end  63 . Upon insertion into the slot  60 , pressure is applied to force the plug  31  to seat proximate the shoulder  68 . Upon application of appropriate pressure, the ridges  36  are forced to deform so as to seat within the recesses  35 , thereby frictionally holding the plug  31  in place. As shown in FIG. 5B, the pin  42  is preferably separated from contact with the plug  31  by the sleeve  41 . The plug  31  protects the cells  40  from interaction with the ground. The plug  31  is preferably made of bronze, although other, similar materials also could be used. The plug  31  should be made of an appropriate material based on its hardness, durability and ductility, as appreciated by those skilled in the art. Bronze, for instance, allows a sufficient level of ductility to allow an appropriate level of flexing. 
     The final assembly process is to grind or otherwise remove the excess material from the plug  31 , so that the plug  31  lies flush with the sole  14  of the body  11 . As shown in FIG. 6, a badge  51  may also be used, which is preferably seated on the cavity rim  22  as shown at location  50 . 
     The preferred club head  10  has improved feel, improved vibration damping characteristics, and reduced stiffness, as compared to prior clubs in the art. Further, the preferred club head  10  may have advantageous weight distribution properties. The apertures  64  formed within the sole bar  26  reduce the stiffness of the lower part of the club  10  due to the removal of material and the elimination of a singular mass of material. The removal of the material, by itself, can lead to improved feel. 
     The use and placement of the cells  40  can also have a dramatic effect on the ability of the preferred club head  10  to absorb shock and to improve the feel. The cells  40  work in the following manner. When a golf ball (not shown) is struck by the club head, the collision generally causes vibration in the head. Low frequency vibrations can be felt with the hands, and can be unpleasant. High frequency vibrations can be audible, and can lead to an unpleasant and inconsistent sound. 
     With reference now to FIG. 5B, if the depicted club head  10  were moving to the right to contact a golf ball (not shown), the club head&#39;s velocity would be slowed at impact. However, because the pins  42  are not fixedly attached to the body  11 , the momentum of the pins  42  would continue to drive them forwardly. The sleeves  41  would compress and cushion the deflection of the pins  42 , thereby keeping the pins separated from the body while at the same time absorbing some of the energy imparted on the club head  10  due to the collision with the ball. Two major effects are caused by the configuration of the cells  40 . First, there are viscous effects. Due to the material properties of the sleeve  41 , the sleeves are compressed and then released as the pins  42  rebound off of the sleeves  41 . Second, there are frictional effects. After impact, upon the excitation of vibration modes and multiple deflections, the pins  42  are jostled around within the sleeves  41 , rubbing, sliding and shaking in the head like mini pistons. This contact between the sleeves  41  and the pins  42  caused by micro-motions also dissipates energy in the form of heat due to friction. The frictional effects may be greater than the viscous effects. With the preferred five cells  40  working simultaneously, energy is being removed by multiple sources. 
     In a similar fashion, the plug  31  can also dissipate or absorb vibration. Because the plug  31  preferably is constructed of a material that is different than the body  11 , those different materials can result in a further dissipation of energy. 
     FIG. 7 depicts a second embodiment of a golf club head  10  in accordance with the present invention. In this embodiment, a cartridge  70  is used with a club head body  11  that is substantially similar to the body shown in FIGS. 1-6. In this second embodiment, the cartridge  70  functions to provide similar benefits to those described for the first embodiment. This includes viscous effects and frictional effects. 
     The second embodiment preferably uses a substrate  71  that is inserted into a slot  77  having sides  78 . The slot  77  is preferably formed within the club head body, proximate the sole bar  26 . The slot  77  may vary in thickness, length and distance from the face, so as to allow various performance changes to the club head. Further, the slot  77  may extend from the sole  14  to the cavity rim  22 , or some portion thereof. 
     The substrate  71  preferably is constructed of bronze, although other conventional materials alternatively can be used, including metals such as aluminum or tungsten, or non-metals such as carbon fiber. The substrate  71  generally should be sufficiently durable and ductile. The preferred substrate  71  has a plurality of interstices  72  formed therein, which may be filled with a polymer, such as polyurethane, or other similar materials having a hardness and a modulus of elasticity that are lower than those of the body  11 , and that are easy to manufacture. For example, the preferred material, urethane, is sufficiently elastic and can be injection molded, so that it is readily manufacturable. 
     The cartridge  70  has a toe end  74 , a heel end  75 , a top side  76  and a cartridge sole  73 . When assembled, the cartridge  70  is inserted into the slot  77  and is attached using means known in the art. The toe end  74  of the cartridge  70  is positioned proximate the toe  13  of the body, the heel end  75  is positioned proximate the heel  12  of the body  11 , and the cartridge sole  73  is positioned proximate the sole  14  of the body  11 . The top side  76  of the cartridge is positioned proximate the cavity  20 . If the slot  77  extends completely through to the cavity  20 , the cartridge  70  may also extend to the cavity  20 , or a portion thereof. 
     The second preferred embodiment of FIG. 7 provides many of the benefits of the first preferred embodiment of FIGS. 1-6. In a manner similar to the preferred embodiment, the cartridge shown in FIGS. 7,  7 A and  7 B can provide an improved club head feel, improved vibration damping characteristics, and reduced stiffness as compared to prior clubs in the art. The slot  77  formed within the sole bar  26  may reduce the stiffness of the lower part of the club  10  due to the removal of material and the elimination of a singular mass of material. 
     The use of the cartridge  70  can also dramatically affect the ability of the club head  10  to absorb shock and to improve the feel. The substrate  71 , combined with the interstices  72  filled with a polymer, can help reduce vibration, due to the absorption of energy by the polymer, and due to the geometry of the slot  77 , which impedes vibration. 
     FIG. 8 depicts a third preferred embodiment of a golf club head  10  in accordance with the present invention. In this embodiment, a cartridge  80  is used with a club head body  11  that is substantially similar to the body shown in FIGS. 1-6 and the body shown in FIGS. 7,  7 A and  7 B. In this third embodiment, the cartridge  80  functions to provide similar benefits to those described for the first and second embodiments. 
     The third preferred embodiment preferably uses a substrate  81  that is inserted into a slot  87  having sides  88 . The slot  87  preferably is formed within the club head body, proximate the sole bar  26 , similar to the second embodiment shown in FIG.  7 . The slot  87  may vary in thickness, length and distance from the face, so as to allow various performance changes to the club head. Further, the slot  87  may extend from the sole  14  to the cavity rim  22 , or some portion thereof. 
     The substrate  81  preferably is constructed of bronze, although various metals and other similar materials may alternatively be used, as are known in the art, similar to those mentioned for the second embodiment. The preferred substrate  81  may have a plurality of interstices  82  formed therein, which function to reduce the stiffness of the substrate  81 . 
     Like the second preferred embodiment, this cartridge  80  has a toe end  84 , a heel end  85 , a top side  86  and a cartridge sole  83 . When assembled, the cartridge  80  is inserted into the slot  87  and attached using means known in the art. The toe end  84  of the cartridge is positioned proximate the toe  13  of the body, the heel end  85  is positioned proximate the heel  12  of the body  11 , and the cartridge sole  83  is positioned proximate the sole  14  of the body  11 . The top side  86  of the cartridge is positioned proximate the cavity  20 . If the slot  87  extends completely through to the cavity  20 , the cartridge  80  may also extend to the cavity  20 , or a portion thereof. 
     The third embodiment may have a sleeve  90  that is positioned proximate the cartridge  80 . The sleeve  90  is formed so that it has two planar sides  91  and a sleeve top  92 . When assembled, the sleeve  90  folds over the cartridge  80 . The sleeve top  92  mounts proximate the top side  86  of the cartridge  80 , and the sides  91  drape over the sides of the substrate  81 . The preferred sleeve  90  may have plurality of nubs  95  formed therein, which can provide improved performance characteristics. Preferably, the nubs  95  are positioned on the surface of the sleeve  90  that lies proximate the body  11 . The nubs  95  reduce the surface area of contact between the cartridge  80  and body  11 . During ball contact, energy is more efficiently transferred to, and absorbed by, the preferred polymer sleeve  90 . 
     The third preferred embodiment provides many of the benefits of the other embodiments. In a manner similar to the other embodiments, the cartridge  80  shown in FIGS. 8,  8 A and  8 B can improve club head feel, improve vibration damping characteristics, and reduce stiffness as compared to prior clubs in the art. The slot  87  formed within the sole bar  26  reduces the stiffness of the lower part of the club  10  due to the removal of material and elimination of a singular mass of material. 
     The use of the cartridge  80  also can dramatically affect the ability of the club head  10  to absorb shock and to improve the feel. The substrate  81 , combined with the interstices  82 , which may be filled with a polymer or left as a void, can help reduce vibration, due to the absorption of energy by the polymer, and due to the geometry of the slot  87 , which impedes vibration. The use of the sleeve  90  provides an additional layer of material to absorb vibration. 
     Although the invention has been disclosed in detail with reference only to the preferred embodiments, those skilled in the art will appreciate that golf club heads can be made without departing from the scope of the invention. Accordingly, the invention is defined only by the claims set forth below.