Patent Publication Number: US-11642577-B2

Title: Golf club heads and methods to manufacture golf club heads

Description:
CROSS REFERENCE 
     This application is a continuation-in-part of application Ser. No. 17/099,362, filed Nov. 16, 2020, which is a continuation of application Ser. No. 16/820,136, filed Mar. 16, 2020, now U.S. Pat. No. 10,874,919, which is a continuation of application Ser. No. 16/590,105, filed Oct. 1, 2019, now U.S. Pat. No. 10,632,349, which claims the benefit of U.S. Provisional Application No. 62/908,467, filed Sep. 30, 2019, U.S. Provisional Application No. 62/903,467, filed Sep. 20, 2019, U.S. Provisional Application No. 62/877,934, filed Jul. 24, 2019, U.S. Provisional Application No. 62/877,915, filed Jul. 24, 2019, U.S. Provisional Application No. 62/865,532, filed Jun. 24, 2019, U.S. Provisional Application No. 62/826,310, filed Mar. 29, 2019, and U.S. Provisional Application No. 62/814,959, filed Mar. 7, 2019. 
     U.S. patent application Ser. No. 17/099,362 is a continuation-in-part of application Ser. No. 16/774,449, filed Jan. 28, 2020, which is a continuation of application Ser. No. 16/179,406, filed Nov. 2, 2018, now U.S. Pat. No. 10,583,336, which claims the benefit of U.S. Provisional Application No. 62/581,456, filed Nov. 3, 2017.” 
     This application is a continuation-in-part of application Ser. No. 16/789,167, filed Feb. 12, 2020. 
     This application is a continuation of U.S. Application Ser. No. 16/702,063, filed Dec. 3, 2019, which claims the benefit of U.S. Provisional Application No. 62/775,022, filed Dec. 4, 2018. 
     The disclosures of the above-referenced applications are incorporated by reference herein in their entirety. 
    
    
     COPYRIGHT AUTHORIZATION 
     The present disclosure may be subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the present disclosure and its related documents, as they appear in the Patent and Trademark Office patent files or records, but otherwise reserves all applicable copyrights. 
     FIELD 
     The present disclosure generally relates to golf equipment, and more particularly, to golf club heads and methods to manufacturing golf club heads. 
     BACKGROUND 
     Various materials (e.g., steel-based materials, titanium-based materials, tungsten-based materials, etc.) may be used to manufacture golf club heads. By using multiple materials to manufacture golf club heads, the position of the center of gravity (CG) and/or the moment of inertia (MOI) of the golf club heads may be optimized to produce certain trajectory and spin rate of a golf ball. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 ,  2 ,  3 , and  4    depict a bottom perspective view, a toe-side perspective view, a heel-side perspective view, and a cross-sectional perspective view (along line  4 - 4  of  FIG.  1   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  5 ,  6 , and  7    depict a top view, a schematic cross-sectional view (along line  6 - 6  of  FIG.  5   ), and a front view, respectively, of a golf club head according to another embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  8 ,  9 , and  10    depict a top view, a schematic cross-sectional view (along line  9 - 9  of  FIG.  8   ), and a front view, respectively, of a golf club head according to another embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  11 ,  12 , and  13    depict a top view, a schematic cross-sectional view (along line  12 - 12  of  FIG.  11   ), and another schematic cross-sectional view (along line  12 - 12  of  FIG.  11   ), respectively, of a golf club head according to yet another embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  14 ,  15 ,  16 ,  17 ,  18 ,  19 ,  20 ,  21 ,  22 ,  23 , and  24    depict a perspective back view, a perspective cross-sectional view (along line  15 - 15  of  FIG.  14   ), a perspective cross-sectional view (taken at line  16 - 16  of  FIG.  14   ), a perspective cross-sectional view (along line  17 - 17  of  FIG.  14   ), a perspective cross-sectional view (along line  18 - 18  of  FIG.  14   ), a perspective cross-sectional view (along line  19 - 19  of  FIG.  14   ), a perspective cross-sectional view (along line  20 - 20  of  FIG.  14   ), another perspective cross-sectional view (along line  15 - 15  of  FIG.  14   ), another perspective cross-sectional view (along line  19 - 19  of  FIG.  14   ), a front perspective view of the golf club head of  FIG.  14    shown without a face portion, and a back side of a face portion for the golf club head of  FIG.  14   , respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  25    depicts one manner in which the example golf club head of  FIG.  14    may be manufactured. 
         FIGS.  26 ,  27 , and  28    depict a perspective cross-sectional view (along line  26 - 26  of  FIG.  27   ), a perspective cross-sectional view (along line  27 - 27  of  FIG.  26   ), and a perspective cross-sectional view (along line  28 - 28  of  FIG.  26   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  29 ,  30 , and  31    depict a perspective cross-sectional view (along line  29 - 29  of  FIG.  30   ), a perspective cross-sectional view (along line  30 - 30  of  FIG.  29   ), and a perspective cross-sectional view (along line  31 - 31  of  FIG.  29   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  32 ,  33 , and  34    depict a perspective cross-sectional view (along line  32 - 32  of  FIG.  33   ), a perspective cross-sectional view (along line  33 - 33  of  FIG.  32   ), and a perspective cross-sectional view (along line  34 - 34  of  FIG.  32   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  35 ,  36 , and  37    depict a perspective cross-sectional view (along line  35 - 35  of  FIG.  36   ), a perspective cross-sectional view (along line  36 - 36  of  FIG.  35   ), and a perspective cross-sectional view (along line  37 - 37  of  FIG.  35   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  38 ,  39 , and  40    depict a perspective cross-sectional view (along line  38 - 38  of  FIG.  39   ), a perspective cross-sectional view (along line  39 - 39  of  FIG.  38   ), and a perspective cross-sectional view (along line  40 - 40  of  FIG.  38   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  41 ,  42 , and  43    depict a perspective cross-sectional view (along line  41 - 41  of  FIG.  42   ), a perspective cross-sectional view (along line  42 - 42  of  FIG.  41   ), and a perspective cross-sectional view (along line  43 - 43  of  FIG.  41   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  44    is a perspective cross-sectional view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  45    is a perspective cross-sectional view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  46    is a perspective cross-sectional view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  47    depicts a manner in which an example golf club head described herein may be manufactured. 
         FIGS.  48 ,  49 ,  50 ,  51 ,  52 , and  53    depict a perspective front view, a perspective back view, a perspective front view shown without a face portion, a perspective cross-sectional view (along line  51 - 51  of  FIG.  49   ), a perspective cross-sectional view (along line  52 - 52  of  FIG.  49   ), and a perspective cross-sectional view (along line  53 - 53  of  FIG.  49   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  54 ,  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61 ,  62 ,  63 ,  64 , and  65    depict a perspective front view, a perspective back view, a perspective cross-sectional view (along line  56 - 56  of  FIG.  55   ), a perspective cross-sectional view (along line  57 - 57  of  FIG.  55   ), and a perspective cross-sectional view (along line  58 - 58  of  FIG.  55   ), a perspective front view shown without a face portion, another perspective front view shown without a face portion, another perspective front view shown without a face portion, a perspective cross-sectional view (along line  62 - 62  of  FIG.  54   ), a perspective cross-sectional view (along line  63 - 63  of  FIG.  54   ), and a perspective cross-sectional view (along line  64 - 64  of  FIG.  54   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  65    depicts a back view of a face portion of a golf club head according to any embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  66    depicts a manner in which an example golf club head described herein may be manufactured. 
         FIGS.  67 ,  68 ,  69 ,  70 ,  71 , and  72    depict a perspective front view, a perspective back view, a perspective front view shown without a face portion, a perspective cross-sectional view (along line  70 - 70  of  FIG.  68   ), a perspective cross-sectional view (along line  71 - 72  of  FIG.  68   ), and a perspective cross-sectional view (along line  72 - 72  of  FIG.  68   ), respectively, of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  73  and  74    depict a front perspective view and a rear perspective view, respectively, of a filler insert according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  75    depicts a perspective cross-sectional view of the golf club head of  FIG.  67    taken at line  71 - 71  of  FIG.  68    with a filler insert according to another embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  76 ,  77 , and  78    depict a front perspective view, a rear perspective view, and a side perspective view of the filler insert of  FIG.  75   . 
         FIGS.  79 ,  80 ,  81 ,  82 ,  83 ,  84 ,  85 , and  86    depict perspective cross-sectional views of the golf club head of  FIG.  67    taken at line  71 - 71  of  FIG.  68    with filler inserts according to several embodiments of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  87    depicts an example of manufacturing a golf club head according to any embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  88  and  89    depict cross-sectional views of two examples of face portions according to any embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  90    depicts a top view of a mass portion according to any embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIGS.  91  and  92    depict side views of example mass portions according to any embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  93    depicts a cross-sectional view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG.  94    depicts a rear view of a portion of the golf club head of  FIG.  93   . 
         FIG.  95    depicts a golf club according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
     
    
    
     For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the present disclosure. Additionally, elements in the drawing figures may not be depicted to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present disclosure. 
     DESCRIPTION 
     The following U.S. Patents and Patent Applications, which are collectively referred to herein as “the incorporated by reference applications,” are incorporated by reference herein in their entirety: U.S. Pat. Nos. 8,961,336; 9,199,143; 9,421,437; 9,427,634; 9,468,821; 9,533,201; 9,610,481; 9,649,542; 9,675,853; 9,814,952; 9,878,220; 10,029,158; 10,029,159; 10,159,876; 10,232,235; 10,265,590; 10,279,233; 10,286,267; 10,293,229; 10,449,428; 10,478,684; 10,512,829; 10,596,424; 10,596,425; 10,632,349; 10,716,978; 10,729,948; 10,729,949; 10,814,193; 10,821,339; 10,821,340; 10,828,538; 10,864,414; 10,874,919; 10,874,921; and U.S. patent application Ser. No. 15/628,251, filed Jun. 20, 2017; U.S. patent application Ser. No. 15/631,610, filed Jun. 23, 2017; U.S. patent application Ser. No. 15/701,131, filed Sep. 11, 2017; U.S. patent application Ser. No. 15/785,001, filed Oct. 16, 2017; U.S. patent application Ser. No. 15/791,020, filed Oct. 23, 2017; U.S. patent application Ser. No. 15/842,591, filed Dec. 14, 2017; U.S. patent application Ser. No. 15/876,877, filed Jan. 22, 2018; U.S. patent application Ser. No. 15/890,961, filed Feb. 7, 2018; U.S. patent application Ser. No. 15/947,383, filed Apr. 6, 2018; U.S. patent application Ser. No. 15/958,288, filed Apr. 20, 2018; U.S. patent application Ser. No. 16/052,254, filed Aug. 1, 2018; U.S. patent application Ser. No. 16/376,863, filed Apr. 5, 2019; U.S. patent application Ser. No. 16/376,868, filed Apr. 5, 2019; U.S. patent application Ser. No. 16/388,619, filed Apr. 18, 2019; U.S. patent application Ser. No. 16/388,645, filed Apr. 18, 2019; U.S. patent application Ser. No. 16/566,597, filed Sep. 10, 2019; U.S. patent application Ser. No. 16/785,336, filed Feb. 7, 2020; U.S. patent application Ser. No. 16/785,340, filed Feb. 7, 2020; U.S. patent application Ser. No. 16/789,167, filed Feb. 12, 2020; U.S. patent application Ser. No. 16/929,552, filed Jul. 15, 2020; U.S. patent application Ser. No. 16/939,284, filed Jul. 27, 2020; U.S. patent application Ser. No. 16/997,091, filed Aug. 19, 2020; U.S. patent application Ser. No. 17/032,253, filed Sep. 25, 2020; U.S. patent application Ser. No. 17/038,155, filed Sep. 30, 2020; U.S. patent application Ser. No. 17/038,195, filed Sep. 30, 2020; U.S. patent application Ser. No. 17/066,271, filed Oct. 8, 2020; U.S. patent application Ser. No. 17/099,362, filed Nov. 16, 2020. 
     In general, golf club heads, golf clubs, and methods to manufacture golf club heads and golf clubs are described herein. In the example of  FIGS.  1 - 4   , a golf club head  100  may include a body portion  110  with a top portion  130  having a crown portion  135 , a bottom portion  140 , a toe portion  150 , a heel portion  160 , a front portion  170 , and a rear portion  180 . The crown portion  135  may be a separate piece that may be attached to the top portion  130  and constructed from a composite material. The bottom portion  140  may include a skirt portion (not shown) defined as a side portion of the golf club head  100  between the top portion  130  and the bottom portion  140  excluding the front portion  170  and extending across a periphery of the golf club head  100  from the toe portion  150 , around the rear portion  180 , and to the heel portion  160 . The front portion  170  may include a face portion  175  to engage a golf ball (not shown). The golf club head  100  may have a neutral axis  401 . The neutral axis  401  may be perpendicular to the face portion  175  and may intersect a center of the face portion  175 . The body portion  110  may also include a hosel portion  165  for receiving a shaft (an example golf club  9500  having a golf club head  9502 , a shaft  9504 , and a grip  9506  is shown in  FIG.  95   ). Alternatively, the body portion  110  may include a bore instead of the hosel portion  165 . The body portion  110  may be made from any one or a combination of materials described herein or described in any of the incorporated by reference applications. A maximum front-to-rear distance of the golf club head  100  may be greater than a maximum heel-to-toe distance of the golf club head  100 . Although  FIGS.  1 - 4    may depict a particular type of golf club head (e.g., driver-type club head), the apparatus methods, and articles of manufacture described herein may be applicable to other types of club heads (e.g., a fairway wood-type club head, a hybrid-type club head, an iron-type club head, a putter-type club head). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The bottom portion  140  may include a plurality of port regions, which are shown for example as a first port region  210  with a first set of ports  211  (generally shown as ports  212 ,  214 , and  216 ) near the toe portion  150 , a second port region  220  with a second set of ports  220  (generally shown as ports  222 ,  224 , and  226 ) near the front portion  170 , and a third port region  230  with a third set of ports  231  (generally shown as ports  232 ,  234 , and  236 ) near the heel portion  160 . Although  FIGS.  1 - 4    show a certain configuration of port regions and ports, the number of port regions, the number and configuration of ports in each region, and the location of the ports may be similar to any of the golf club heads described herein on in any of the incorporated by reference applications. The body portion  110  may also include a plurality of mass portions, shown as a first set of mass portions  260  (generally shown as mass portions  262 ,  264 , and  266 ), a second set of mass portions  270  (generally shown as mass portions  272 ,  274 , and  276 ), and a third set of mass portions  280  (generally shown as mass portions  282 ,  284  and  286 ). Each port may interchangeably receive any of the mass portions. The masses of the first set of mass portion  260 , the second set of mass portions  270  and/or the third set of mass portions  280  may be similar or different. Accordingly, by using mass portions having similar or different masses in each of the ports of the port regions  210 ,  220  and/or  230 , the overall mass in each port region and/or the mass distribution in each port region may be adjusted as described herein and in any of the incorporated by reference applications to generally optimize and/or adjust the swing weight, center of gravity, moment of inertia, and/or an overall feel of the golf club head for an individual using the golf club head  100 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Certain regions of the interior of the body portion  110  may include a polymer material, which may also be referred to herein as the filler material, similar to any of the polymer materials described herein or described in any of the incorporated by reference applications. The filler material may dampen vibration, dampen noise, lower the center of gravity and/or provide a better feel and sound for the golf club head  100  when striking a golf ball (not shown). The golf club head  100 , may have one or more interior regions and/or cavities that may include a filler material similar to any of the golf club heads described herein or described in any of the incorporated by reference applications. In one example, as shown in  FIG.  4   , the body portion  110  may include a cavity wall portion  320 . The cavity wall portion  320  may form a first interior cavity portion  410  and a second interior cavity portion  420  within the body portion  110 . The first interior cavity portion  410  and the second interior cavity portion  420  may be separated by the cavity wall portion  320 . Alternatively, the first interior cavity portion  410  and the second interior cavity portion  420  may be connected through one or more openings in the cavity wall portion  320 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As illustrated in  FIG.  4   , the cavity wall portion  320  may include a first portion  322  extending from a location at or proximate to the top portion  130  toward the bottom portion  140 . The first portion  322  may extend toward the bottom portion  140  at a certain angle or orientation relative to the face portion  175 . In one example, the first portion  322  may extend toward the bottom portion  140  and away from the face portion  175 . Accordingly, a first width  411  (W C1 ) of the first interior cavity portion  410  may increase in a direction from the top portion  130  to the bottom portion  140 . In another example, the first portion  322  may extend toward the bottom portion  140  and toward the face portion  175 . Accordingly, the first width  411  of the first interior cavity portion  410  may decrease in a direction from the top portion  130  to the bottom portion  140 . In the illustrated example of  FIG.  4   , the first portion  322  of the of the cavity wall portion  320  may extend from a location at or proximate to the top portion  130  generally parallel or substantially parallel with the face portion  175 . Accordingly, the first width  411  of the first interior cavity portion  410  may be constant or substantially constant. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first interior cavity portion  410  may include an enlarged cavity portion  412  between the top portion  130  and the bottom portion  140 . As shown in the illustrated example of  FIG.  4   , the enlarged cavity portion  412  extends partially or fully over the second port region  220 . Accordingly, the enlarged cavity portion  412  may have a second width  413  (W C2 ) of the first interior cavity portion  410  that may be greater than the first width  411  of the first interior cavity portion  410 . The second width  413  may be about two times greater than the first width  411 . The second width  413  may be at least two times greater than the first width  411 . The enlarged cavity portion  412  may be located at least partially below the neutral axis  401  of the golf club head  100 . The enlarged cavity portion  412  may be located wholly below a neutral axis  401  of the golf club head  100 . The first width  411  may be located above the neutral axis  401 . The second width  413  may be located below the neutral axis  401 . The enlarged cavity portion  412  may be defined by a second wall portion  324  that may extend from the first wall portion  322  toward the rear portion  180  and the bottom portion  140 , and traverse back over the second port region  220 . The first interior cavity portion  410  may include a third wall portion  326  that extends from the second wall portion  324  to a location at or proximate to the bottom portion  140 . The first interior cavity portion  410  may have a third width  414  (W C3 ) extending from the third wall portion  326  to the back surface  176  of the face portion  175 . The third width  414  may be located below the enlarged cavity portion  412 . The third width  414  may be located below the second width  413 . The third width  414  may be less than the second width  413 . The third width  414  may be substantially equal to the first width  411 . As shown in the illustrated example of  FIG.  4   , the third width  414  may be located between the second port region  220  and the face portion  175 . The third width  414  may be located proximate to the bottom portion. In another example, the first width  411  may be similar to the second width  413  of the first interior cavity portion  410  (not shown). Accordingly, the first wall portion  322  of the cavity wall portion  320  may located farther back toward the rear portion  180  than the location of the first wall portion  322  shown in  FIG.  4    such that the portion of the first interior cavity portion  410  above the second port region  220  extends over the one or more ports of the second port region  220 . In other examples, the first interior cavity portion  410  may be configured similar any of the interior cavities described herein and shown in  FIGS.  5 - 13   . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the first interior cavity portion  410  may be unfilled (i.e., empty space). Alternatively, the first interior cavity portion  410  may be partially (i.e., less than 100% filled) or entirely filled with a filler material (i.e., a cavity filling portion) to absorb shock, isolate vibration, dampen noised, and/or provide structural support for the face portion. For example, at least 50% of the first interior cavity portion  410  may be filled with a TPE material to absorb shock, isolate vibration, and/or dampen noise when the golf club head  100  strikes a golf ball via the face portion  175 . In one example, the first interior cavity portion  410  may be partially or entirely filled with a filler material through a port (e.g. port  224 ) located in the bottom portion  140 . In one example, as shown in  FIG.  4   , the port  224  may include an opening that accesses the first interior cavity portion  410 . The opening may provide a fluid pathway for filler material to be introduced to the first interior cavity portion  410 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     When the face portion  175  of the golf club head  100  strikes a golf ball, the face portion  175  and the filler material may deform and/or compress. The kinetic energy of the impact may be transferred to the face portion  175  and/or the filler material. For example, some of the kinetic energy may be transformed into heat by the filler material or work done in deforming and/or compressing the filler material. Further, some of the kinetic energy may be transferred back to the golf ball to launch the golf ball at a certain velocity. A filler material with a relatively higher COR may transfer relatively more kinetic energy to the golf ball and dissipate relatively less kinetic energy. Accordingly, a filler material with a relatively high COR may generate relatively higher golf ball speeds because a relatively greater part of the kinetic energy of the impact may be transferred back to the golf ball to launch the golf ball from the golf club head  100 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     With the support of the cavity wall portion  320  to form the first interior cavity portion  410  and filling at least a portion of the first interior cavity portion  410  with a filler material, the face portion  175  may be relatively thin without degrading the structural integrity, sound, and/or feel of the golf club head  100 . In one example, the face portion  175  may have a thickness of less than or equal to 0.075 inch (e.g., a distance between a front surface  174  and the back surface  176 ). In another example, the face portion  175  may have a thickness of less than or equal to 0.2 inch. In another example, the face portion  175  may have a thickness of less than or equal to 0.06 inch. In yet another example, the face portion  175  may have a thickness of less than or equal to 0.05 inch. Further, the face portion  175  may have a thickness of less than or equal to 0.03 inch. In yet another example, a thickness of the face portion  175  may be greater than or equal to 0.03 inch and less than or equal to 0.2 inch. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the illustrated example of  FIGS.  1 - 4   , the second interior cavity portion  420  may be unfilled (i.e., empty space). Alternatively (not shown), the second interior cavity portion  420  may be partially or entirely filled with a filler material (i.e., a cavity filling portion), which may include one or more similar or different types of materials described herein and may be different or similar to the filler material used to fill the first interior cavity portion  410 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     While each of the examples herein may describe a certain type of golf club head, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of golf club heads. Referring to  FIGS.  5 - 7   , for example, a golf club head  500  may include a body portion  510  and a cavity wall portion  520 . Although  FIGS.  5 - 7    may depict a particular type of club head (e.g., a fairway wood-type club head), the apparatus, methods, and articles of manufacture described herein may be applicable to other types of club head (e.g., a driver-type club head, a hybrid-type club head, an iron-type club head, a putter-type club head, etc.). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  510  may include a toe portion  540 , a heel portion  550 , a front portion  560 , a rear portion  570 , a top portion  580  (e.g., a crown portion), and a bottom portion  590  (e.g., a sole portion). The front portion  560  may include a face portion  562  (e.g., a strike face). The face portion  562  may include a front surface  564  and a back surface  566 . The front surface  564  may include a plurality of grooves, generally shown as  710  in  FIG.  7   . The cavity wall portion  520  may form a first interior cavity portion  610  and a second interior cavity portion  620  within the body portion  510 . As illustrated in  FIG.  6   , for example, the cavity wall portion  520  may extend from the back surface  566  of the face portion  562 . The cavity wall portion  520  may be a single curved wall section. In particular, the cavity wall portion  520  may have a convex arc profile relative to the back surface  566  (e.g., C shape) to form a dome-like structure with an elliptical base (e.g.,  FIG.  7   ) or a circular base on the back surface  566 . In another example, the cavity wall portion  520  may form a cone-like structure or a cylinder-like structure with the body portion  510 . Alternatively, the cavity wall portion  520  may be a concave arc profile relative to the back surface  566 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first interior cavity portion  610  may be partially or entirely filled with a suitable filler material such as any of the filler materials described herein or described in any of the incorporated by reference applications to absorb shock, isolate vibration, dampen noise, and/or provide structural support. The elastic polymer material may be injected into the first interior cavity portion  610  via an injection molding process via a port on the face portion  562 . With the support of the cavity wall portion  520  to form the first interior cavity portion  610  and filling at least a portion of the first interior cavity portion  610  with an elastic polymer material, the face portion  562  may be relatively thin without degrading the structural integrity, sound, and/or feel of the golf club head  500 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The cavity wall portion  520  may include multiple sections. Turning to  FIGS.  8 - 10   , for example, a golf club head  800  may include a body portion  810  and a cavity wall portion  820 . The body portion  810  may include a toe portion  840 , a heel portion  850 , a front portion  860 , a rear portion  870 , a top portion  880  (e.g., a crown portion), and a bottom portion  890  (e.g., a sole portion). The front portion  860  may include a face portion  862  (e.g., a strike face) with a front surface  864  and a back surface  866 . The cavity wall portion  820  may extend from the back surface  866  to form a first interior cavity portion  910  and a second interior cavity portion  920  within the body portion  810 . The cavity wall portion  820  may include two or more wall sections, generally shown as  930 ,  940 , and  950  in  FIG.  9   . Similar to the first interior cavity portion  610  ( FIGS.  5 - 7   ), the first interior cavity portion  910  may be partially or entirely filled with a filler material. The filler material may be injected into the first interior cavity portion  910  via an injection molding process via a port on the face portion  862 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As illustrated in  FIGS.  11  and  12   , for example, a golf club head  1100  may include a body portion  1110  and a cavity wall portion  1120 . The body portion  1110  may include a toe portion  1140 , a heel portion  1150 , a front portion  1160 , a rear portion  1170 , a top portion  1180  (e.g., a crown portion), and a bottom portion  1190  (e.g., a sole portion). The front portion  1160  may include a face portion  1162  (e.g., a strike face) with a front surface  1164  and a back surface  1166 . The face portion  1162  may be associated with a loft plane  1230  that defines the loft angle of the golf club head  1100 . The cavity wall portion  1120  may be a single flat wall section. In particular, the cavity wall portion  1120  may extend between the toe portion  1140  and the heel portion  1150  and between the top portion  1180  and the bottom portion  1190  to form a first interior cavity portion  1210  and a second interior cavity portion  1220  within the body portion  1110 . The cavity wall portion  1120  may be parallel or substantially parallel to the loft plane  1230 . Alternatively, as shown in  FIG.  13   , a cavity wall portion  1320  may be perpendicular or substantially perpendicular to a ground plane  1330 . Similar to the interior cavity  610  portion ( FIGS.  5 - 7   ) and interior cavity  910  portion ( FIGS.  8 - 10   ), the first interior cavity portion  1210  may be partially or entirely filled with an elastic polymer or elastomer material. The elastic polymer material may be injected into the first interior cavity portion  1210  via an injection molding process via a port on the face portion  1162  and/or the bottom portion  1190  as described herein or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Alternatively, the cavity wall portion  1120  may extend between the bottom portion  1190  and a top-and-front transition region (i.e., a transition region between the top portion  1180  and the front portion  1160 ) so that the cavity wall portion  1120  and the loft plane  1230  may not be parallel to each other. In another example, the cavity wall portion  1120  may extend between the top portion  1180  and a bottom-and-front transition region (i.e., a transition region between the bottom portion  1190  and the front portion  1160 ) so that the cavity wall portion  1120  and the loft plane  1230  may be not parallel to each other. Although  FIGS.  11 - 13   , may depict the cavity wall portions  1120  and  1320  being flat or substantially flat, the cavity wall portions  1120  and/or  1320  may be concave or convex relative to the face portion  1162 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  14 - 24   , a golf club head  1400  may include a body portion  1410  having a toe portion  1440 , a heel portion  1450  that may include a hosel portion  1455  configured to receive a shaft (for example the shaft  9504 ) with a grip (for example the grip  9506 ) on one end and the golf club head  1400  on the opposite end of the shaft to form a golf club, a front portion  1460  with a perimeter edge portion  1461 , a back portion  1470 , a top portion  1480 , and a sole portion  1490 . The toe portion  1440 , the heel portion  1450 , the front portion  1460 , the back portion  1470 , the top portion  1480 , and/or the sole portion  1490  may partially overlap each other. The golf club head  1400  may be an iron-type golf club head (e.g., a 1-iron, a 2-iron, a 3-iron, a 4-iron, a 5-iron, a 6-iron, a 7-iron, an 8-iron, a 9-iron, etc.), or a wedge-type golf club head (e.g., a pitching wedge, a lob wedge, a sand wedge, an n-degree wedge such as 44 degrees (°), 48°, 52°, 56°, 60°, etc.). Although  FIGS.  14 - 24    may depict a particular type of club head, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of club heads (e.g., a driver-type club head, a fairway wood-type club head, a hybrid-type club head, a putter-type club head, etc.). The material of construction of the golf club head  1400  and/or any components thereof may be similar to any materials described herein or in any of the incorporated by reference applications for constructing a golf club heads. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  1400  may include a face portion  1462  (i.e., the strike face), which may be integrally formed with the body portion  1410  (e.g., a single unitary piece). In one example, as shown in  FIGS.  14 - 24   , the face portion  1462  may be a separate piece coupled (e.g., adhesively, mechanically, by welding or soldering) to the body portion  1410 . The face portion  1462  may include a front surface  1464  and a back surface  1466 . In one example (not shown), the front portion  1460  may include one or a plurality of recessed shoulders configured to receive the face portion  1462  for attachment of the face portion  1462  to the body portion  1410 . In another example, as shown in  FIGS.  14 - 24   , the back surface  1466  may include a perimeter portion  1467  that may be attached to the perimeter edge portion  1461  of the body portion  1410  to attach the face portion  1462  to the body portion  1410 . The perimeter edge portion  1461  of the body portion  1410  and the perimeter portion  1467  of the face portion  1462  may be attached by one or more fasteners, one or move adhesive or bonding agents, and/or welding or soldering. In one example, as shown in  FIGS.  14 - 24   , the perimeter portion  1467  of the face portion  1462  may be welded to the perimeter edge portion  1461  of the body portion  1410  at one or more locations. Alternatively, the entire perimeter portion  1467  of the face portion  1462  may be welded to the entire perimeter edge portion  1461  of the body portion  1410  (i.e., a continuous weld). The face portion  1462  may include a ball strike region  1468  to strike a golf ball. In one example, the center of the ball strike region  1468  may be a geometric center  1463  of the face portion  1462 . In another example, the geometric center  1463  of the face portion  1462  may be offset from a center of the ball strike region  1468 . In one example, the geometric center  1443  and one or more regions near and/or surrounding the geometric center within the ball strike region  1468  may provide a generally optimum location (i.e., optimum ball distance, ball speed, ball spin characteristics, etc.) on the face portion  1462  for striking a golf ball. In yet another example, any location at or near the geometric center  1463  and within the ball strike region  1468  may provide a generally optimum location on the face portion  1462  for striking a golf ball. However, a ball may be struck with any portion of the face portion  1462  within the ball strike region  1468  or outside the ball strike region  1468  for any of the golf club heads described herein resulting in certain ball flight characteristics different from an on-center hit that may be preferred by an individual. The configuration of the face portion  1462  and the attachment of the face portion  1462  (e.g., welding) to the body portion  1410  may be similar in many respects to the golf club heads described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  1400  may be associated with a ground plane  2310 , a horizontal midplane  2320 , and a top plane  2330 . In particular, the ground plane  2310  may be a plane that is parallel or substantially parallel to the ground and is tangent to the lowermost edge of the sole portion  1490  when the golf club head  1400  is at an address position (e.g., the golf club head  1400  aligned to strike a golf ball). A top plane  2330  may be a plane that is tangent to the uppermost edge of the top portion  1480  when the golf club head  1400  is at the address position. The ground and top planes  2310  and  2330 , respectively, may be parallel or substantially parallel to each other. The horizontal midplane  2320  may be vertically halfway between the ground and top planes  2310  and  2330 , respectively. Further, the golf club head  1400  may be associated with a loft plane  2340  defining a loft angle  2345  (α) of the golf club head  1400 . The loft plane  2340  may be a tangential plane to the face portion  1462 . The loft angle  2345  may be defined by the loft plane  2340  and a vertical plane  2350  normal to the ground plane  2310 . 
     The body portion  1410  may be a hollow body including an interior cavity  1510  having inner walls  1512 . The interior cavity  1510  may extend between the front portion  1460 , the back portion  1470 , the top portion  1480 , and the sole portion  1490 . In the example of  FIGS.  14 - 24   , the interior cavity  1510  of the body portion  1410  may be enclosed with and partially defined with the face portion  1462 . The configuration of the interior cavity  1510  (e.g., height, width, volume, shape, etc.), the configuration of the interior cavity  1510  relative to the body portion  1410  (e.g., volume of the interior cavity  1510  relative to the volume of body portion  1410 ), the width and height variation, and access to the interior cavity  1510  from one or more ports on the body portion  1410  may be similar to the golf club heads described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Further, the body portion  1410  may include one or more ports, which may be exterior ports and/or interior ports (e.g., located inside the body portion  1410 ). The inner walls  1512  of the interior cavity  1510  may include one or more ports. In one example, as shown in  FIG.  14   , the back portion  1470  may include one or more ports along or proximate to a periphery of the body portion  1410 . For example, the body portion  1410  may include a first set of ports  1520  (e.g., shown as ports  1521 ,  1522 , and  1523 ), a second set of ports  1530  (e.g., shown as ports  1531 ,  1532 , and  1533 ), and a third set of ports  1540  (e.g., shown as ports  1541  and  1542 ). The locations, spacing relative to other ports, and any other configuration of each port of the first set of ports  1520 , the second set of ports  1530 , and/or the third set of ports  1540  may be similar in many respects to any of the ports described herein or described in any of the incorporated by reference applications. Further, any one or more of the ports of the first set of ports  1520 , the second set of ports  1530 , and/or the third set of ports  1540  may be connected to interior cavity  1510  through which one or more filler materials may be injected into the interior cavity  1510 . In the example of  FIGS.  14 - 24   , the port  1542  may be connected to the interior cavity  1510  via an opening  1543 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Each port of the first set of ports  1520  may be separated by a distance less than the port diameter of any of the ports of the first set of ports  1520 . Each port of the second set of ports  1530  may be separated by a distance less than the port diameter of any of the ports of the second set of ports  1530 . Each port of the third set of ports third set of ports  1540  may be separated by a distance less than the port diameter of any of the ports of the third set of ports  1540 . The first set of ports  1520  and the second set of ports  1530  may be spaced apart by a distance substantially greater than the port diameter of any of the ports of the first set of ports  1520  and the second set of ports  1530 . In one example, the second set of ports  1530  and the third set of ports  1540  may be spaced apart by a distance less than the port diameter of any of the ports of the second set of ports  1530  and the third set of ports  1540 . In another example, as shown in  FIG.  14   , the second set of ports  1530  and the third set of ports  1540  may be spaced apart by a distance substantially greater than the port diameter of any of the ports of the second set of ports  1530  and the third set of ports  1540 . In one example, the portion of the body portion  1410  between the second set of ports  1530  and the third set of ports  1540  may generally correspond or be aligned with the ball strike region  1468  and may be devoid of any ports. In another example (not shown), the second set of ports  1530  and the third set of ports  1540  may extend continuously and with generally equal port spacing from the toe portion  1440  to the heel portion  1450 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Although the figures may depict the ports as separate and individual parts, each set of the first, second, and third sets of ports  1520 ,  1530 , and  1540 , respectively, may be a single port. In one example, all of the first set of ports  1520  (e.g., shown as  1521 ,  1522 , and  1523 ) may be combined into a single port (e.g., a first port). In another example, all of the second set of ports  1530  (e.g., shown as  1531 ,  1532 , and  1533 ) may be combined into a single port (e.g., a second port). In yet another example, all of the third set of ports  1540  (e.g., shown as  1541  and  1542 ) may be combined into a single port (e.g., a third port). While the figures may depict a particular number of ports, the apparatus, methods, and articles of manufacture described herein may include more or a smaller number of ports. 
     The body portion  1410  may include one or more mass portions (e.g., weight portion(s)), which may be integral mass portion(s) or separate mass portion(s) that may be coupled to the body portion  1410 . In the illustrated example as shown in  FIG.  14   , the body portion  1410  may include a first set of mass portions  1620  (e.g., shown as mass portions  1621 ,  1622 , and  1623 ), a second set of mass portions  1630  (e.g., shown as mass portions  1631 ,  1632 , and  1633 ), and a third set of mass portions  1640  (e.g., shown as mass portions  1641  and  1642 ). While the above example may describe a particular number or portions of mass portions, a set of mass portions may include a single mass portion or a plurality of mass portions as described in any of the incorporated by reference applications. For example, the first set of mass portions  1620  may be a single mass portion (e.g., mass portions  1631 ,  1632 , and  1633  may be a single mass portion referred to as a first mass portion). In a similar manner, the second set of mass portions  1630  and/or the third set of mass portions  1640  may be a single mass portion. Further, the first set of mass portions  1620 , the second set of mass portions  1630 , and/or the third set of mass portions  1640  may be a portion of the physical structure of the body portion  1410 . The mass portions of the first set of mass portions  1620 , the second set of mass portions  1630 , and/or third set of mass portions  1640  may be similar to any of the mass portions described herein or in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  1410  may be made of a first material whereas the mass portions of the first set of mass portions  1620 , the second set of mass portions  1630 , and/or the third set of mass portions  1640  may be made of a second material. The mass portions of the first set of mass portions  1620 , the second set of mass portions  1630 , and/or the mass portions of the third set mass portions  1640  may be similar or different materials. The materials of the body portion  1410  and any of the mass portions of the first set of mass portions  1620 , the second set of mass portions  1630 , and/or the third set mass portions  1640  may be similar to the materials of the body portion and any of the mass portions, respectively, described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  1510  may be partially or entirely filled with one or more filler materials (i.e., a cavity filling material), which may include one or more similar or different types of materials. In one example, as shown in  FIGS.  14 - 24   , the interior cavity  1510  may be filled with a first filler material  1712  and a second filler material  1714 . The first filler material  1712  may be coupled or attached to the back surface  1466  of the face portion  1462 . In one example, the first filler material  1712  may have inherent adhesive or bonding properties to attach to the back surface  1466  of the face portion  1462 . In another example, the first filler material  1712  may be attached to the back surface  1466  of the face portion  1462  with one or more bonding agents or adhesives that may be mixed with the first filler material  1712 . In another example, the first filler material  1712  may be attached to the back surface  1466  of the face portion  1462  with one or more bonding agents or adhesives that may be separate from the first filler material  1712 . In another example, the first filler material  1712  may be maintained in contact with the back surface  1466  of the face portion  1462  with the second filler material  1714  as described herein. In yet another example, the first filler material  1712  may be both bonded to the back surface  1466  of the face portion  1462  as described herein and maintained in contact with the back surface  1466  of the face portion  1462  with the second filler material  1714 . The first filler material  1712  and/or the second filler material  1714  may be similar to the filler materials described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first filler material  1712  may be coupled to at least a portion of the back surface  1466  of the face portion  1462  that corresponds to the ball strike region  1468  of the face portion  1462 . The first filler material  1712  may be coupled to regions of the back surface  1466  of the face portion  1462  that are beyond the ball strike region  1468 . The first filler material  1712  may be coupled to one or more portions the back surface  1466  of the face portion  1462  that is greater than or equal to 10% and less than or equal to 100% of the area back surface  1466  of the face portion  1462  that is exposed to the interior cavity  1510 . The amount of the first filler material  1712  that may be coupled to the back surface  1466  of the face portion  1462  may depend upon the loft angle of the golf club head, the overall thickness of the face portion  1462 , the thickness profile of the face portion  1462 , the shape of the interior cavity  1510 , the locations and configurations of any ports of mass portions, the material properties of the first filler material  1712 , and/or the material properties of the second filler material  1714 . In one example, a relatively large portion of the back surface  1466  of the face portion  1462  may be coupled to the first filler material  1712  for a relatively thin face portion  1462  so that the first filler material  1712  provides sufficient structural support for the face portion  1462 . In another example, a golf club head with a relatively higher loft angle may limit the portions of the back surface  1466  of the face portion  1462  to which the first filler material  1712  may be coupled. In yet another example, the acoustic properties of the golf club head may be a factor in determining the amount of filler material  1712  that may be coupled to the back surface  1466  of the face portion to provide a pleasing sound and feel to an individual. The amount of the first filler material  1712  coupled to the back surface  1466  of the face portion  1462  may (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  1400  strikes a golf ball as perceived by an individual using the golf club head  1400 ), (ii) provide structural support for the face portion  1462 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     A width  1722  (W F1 ) of the first filler material  1712  may vary from the toe portion  1440  to the heel portion  1450  and/or from the top portion  1480  to the sole portion  1490 . The width  1722  of the first filler material  1712  may be constant or substantially constant from the toe portion  1440  to the heel portion  1450  and/or from the top portion  1480  to the sole portion  1490 . The width  1722  of the first filler material  1712  may be constant or substantially constant at one or more locations in the interior cavity  1510  and vary at certain other locations in the interior cavity  1510 . In one example, as shown in  FIGS.  14 - 24   , the width  1722  of the first filler material  1712  may vary at one or more locations in the interior cavity  1510  similar or substantially similar to the contour of all or portions of the inner walls  1512  of the interior cavity  1510  (i.e., similar or substantially similar to the shape of the inner walls  1512  of the interior cavity  1510 ). Accordingly, the amount of the first filler material  1712  in the interior cavity  1510  and/or coupled to the face portion  1462  may be maximized while maintaining a certain gap as further described herein between the first filler material  1712  and the inner walls  1512  of the interior cavity  1510 . In another example, the first filler material  1712  at and/or around the ball strike region  1468  of the face portion  1462  may have a relatively large width  1722  to (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  1400  strikes a golf ball as perceived by an individual using the golf club head  1400 ), (ii) provide structural support for the face portion  1462 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The width  1722  of the first filler material  1712  may be determined at the ball strike region  1468  and/or other regions of the interior cavity  1510  so that a relatively high or optimum coefficient of restitution (COR) is provided for the golf club head  1400 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIGS.  14 - 24   , a distance between the first filler material  1712  and the inner walls  1512  of the interior cavity  1510  may define a gap  1724 . The size of the gap  1724  may be constant or may vary in the interior cavity  1510  similar or substantially similar to the shape of the first filler material  1712 , the shape of the inner walls  1512  of the interior cavity  1510 , the locations of one or more ports that may be connected to the interior cavity  1510 , the locations of one or more integral and/or removable mass portions, and/or other factors as described herein. At certain locations in the interior cavity  1510 , the size of the gap  1724  may be as small as possible yet provide sufficient space to accommodate the second filler material  1714  between the first filler material  1712  and the inner walls  1512  of the interior cavity  1510 . In one example, the gap may be a result of manufacturing the golf club head with the first filler material  1712  and the second filler material  1714 . 
     In one example, the gap  1724  may be greater than or equal to 0.001 inch (0.003 cm) and less than or equal to 0.2 inch (0.508 cm). In another example, the gap  1724  may be greater than or equal to 0.007 inch (0.18 cm) and less than or equal to 0.1 inch (0.384 cm). In another example, the gap  1724  may be greater than or equal to 0.015 inch (0.038 cm) and less than or equal to 0.05 inch (0.127 cm). In yet another example, the gap  1724  may be greater than or equal to 0.003 inch (0.008 cm) and less than or equal to 0.38 inch (0.635 cm). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described herein, the width  1722  of the first filler material  1712  may vary similar or substantially similar to the shape of the inner walls  1512  of the interior cavity  1510 . Accordingly, in one example, the variation in the width of the gap  1724  (Wg) may be expressed by the following equation: 
     
       
         
           
             
               
                 
                   where 
                   : 
                   
                     
                       
                         
                           1 
                           ≤ 
                           
                             
                               Wg 
                               max 
                             
                             
                               Wg 
                               min 
                             
                           
                           ≤ 
                           Rg 
                         
                       
                     
                     
                       
                         
                           
                             
                               Wg 
                               max 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             is 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             the 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             maximum 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             Wg 
                           
                           , 
                         
                       
                     
                     
                       
                         
                           
                             
                               Wg 
                               min 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             is 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             the 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             minimum 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             Wg 
                           
                           , 
                           and 
                         
                       
                     
                     
                       
                         
                           1 
                           &lt; 
                           Rg 
                           ≤ 
                           5 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In one example, R g  may be 2 or less as the width  1722  of the first filler material  1712  varies similar or substantially similar to the shape of the inner walls  1512  of the interior cavity  1510 . In another example, R g  may be 3 or less. Accordingly, the maximum width of the gap  1724  (Wg max ) may be no more than three times the minimum width of the gap  1724  (Wg min ). In yet another example, R g  may be 4 or less. Accordingly, the maximum width of the gap  1724  (Wg max ) may be no more than four times the minimum width of the gap  1724  (Wg min ). The variation in the gap  1724  may be small such that the shape of the first filler material  1712  may vary similar or substantially similar to the contour of the inner walls  1512  of the interior cavity  1510  (i.e., the shape of the inner walls of the interior cavity  1510 ). While the above examples may describe particular ratios of Wg max  to Wg min , the apparatus, methods, and articles of manufacture described herein may include greater ratios of Wg max  to Wg min . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The back surface  1466  of the face portion  1462  may include a perimeter portion  1467 , which may be attached to the perimeter edge portion  1461  of the body portion  1410  as described herein. Accordingly, the back surface  1466  of the face portion  1462  may include an inner surface portion  1469  exposed to the interior cavity  1510 . The inner surface portion  1469  may also define a boundary of the interior cavity  1510  (i.e., the front boundary of the interior cavity  1510 ). In one example (not shown), the first filler material  1712  may be coupled the entire inner surface portion  1469  of the face portion  1462 . In another example, as shown in  FIGS.  14 - 24   , the first filler material  1712  may be coupled to a portion of the inner surface portion  1469  of the face portion  1462 . Accordingly, the first filler material  1712  may include a frontal area  1713  attached to the inner surface portion  1469  of the face portion  1462 . In one example, a relationship between the frontal area  1713  of the first filler material  1712  (the area of the front surface of the first filler material  1712  attached to the face portion  1462 ) (FA m ) and the area of the inner surface portion  1469  of the face portion  1462  (BA f ) may be expressed by the following equation:
 
FA m   =BA   f ( A   1   α+A   2 )  (2)
         where:
           FA m  is the frontal area  1713  of the first filler material  1712 ,   BA f  is the area of the inner surface portion  1469  of the face portion  1462 ,   α is the loft angle of the face portion  1462 ,   −0.003≤A 1 ≤0.001, and   0.4≤A 2 ≤0.85   
               

     The loft angle α as used herein may be associated with the type of iron golf club head such as a 5-iron golf club, a 7-iron golf club, or a wedge-type golf club. For example, a 5-iron golf club head may have a loft angle α of 38°±2°. In another example, a 7-iron golf club head may have a loft angle α of 44°±2°. In yet another example, a wedge-type golf club head may have a loft angle α of 5°±2°. Accordingly, any loft angle expressed herein may vary by ±2° for the same type of iron golf club head. While the above examples may describe particular iron-type golf club heads, the apparatus, methods, and articles of manufacture described herein may include a driver-type golf club head, a fairway-wood-type golf club head, a hybrid-type golf club head, a putter-type golf club head, or other types of golf club heads. Further, although the above examples may describe particular loft angles, the apparatus, methods, and articles of manufacture described herein may include greater or less loft angles. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The upper and lower values of the coefficients A 1  and A 2  may define the upper and lower boundaries of the ratio of the frontal area  1713  of the first filler material  1712  to the area of the inner surface portion  1469  of the face portion  1462 . In one example, according to Equation (2) and assuming a value of −0.0018 for the coefficient A 1 , upper and lower boundaries of a ratio of the frontal area  1713  of the first filler material  1712  to the area of the inner surface portion  1469  of the face portion  1462  for a set of iron-type golf club heads may be determined as shown in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Iron-Type 
                 α 
                 (FA m /BA f )≤ 
                 (FA m /BA f )≥ 
               
               
                   
                   
               
             
            
               
                   
                 3 
                 18 
                 0.77 
                 0.45 
               
               
                   
                 4 
                 21 
                 0.77 
                 0.44 
               
               
                   
                 5 
                 23 
                 0.76 
                 0.44 
               
               
                   
                 6 
                 26 
                 0.76 
                 0.43 
               
               
                   
                 7 
                 30 
                 0.75 
                 0.43 
               
               
                   
                 8 
                 34 
                 0.74 
                 0.42 
               
               
                   
                 9 
                 39 
                 0.73 
                 0.41 
               
               
                   
                 Wedge 
                 44 
                 0.72 
                 0.40 
               
               
                   
                 Gap Wedge 
                 49 
                 0.71 
                 0.39 
               
               
                   
                 Sand Wedge 
                 54 
                 0.71 
                 0.38 
               
               
                   
                 Lob Wedge 
                 59 
                 0.70 
                 0.38 
               
               
                   
                   
               
            
           
         
       
     
     The loft angle of a golf club head may determine the structural configuration of the golf club head. Accordingly, golf club heads with different loft angles may have different internal cavity shapes, port locations, mass portion locations, filler material volumes, different CG locations, different size face portions, or different golf club head cross sectional shapes. In one example, a golf club head with a relatively higher loft angle may have a generally smaller cavity width profile than a golf club head with a lower loft angle. Accordingly, the value of FA m /BA f  for the golf club with the relatively higher loft angle may be generally smaller than the golf club head with the lower loft angle due to the difference in the amount of filler materials that may be provided in the interior cavities of each golf club head as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In another example, a relationship between the volume of the first filler material  1712  and the volume of the interior cavity  1510  (V m ) may be expressed by the following equation:
 
 V   m   =V   c ( B   1   α+B   2 )  (3)
         where:
           V m  is the volume of the first filler material  1712 ,   V c  is the volume of the interior cavity  1510 ,   α is the loft angle,   −0.001≤B 1 ≤0.001, and   0.3≤B 2 ≤0.65   
               

     The upper and lower boundary values of the coefficients B 1  and B 2  may define the upper and lower boundaries of a ratio of the volume of the first filler material  1712  to the volume of the interior cavity  1510 . In one example, according to Equation (3) and assuming a value of −0.0015 for the coefficient B 1 , upper and lower boundaries of a ratio of the volume of the first filler material  1712  to the volume of the interior cavity  1510  for a set of iron-type golf club heads may be determined as shown in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Iron-Type 
                 α 
                 (V m /V c )≤ 
                 (V m /V c )≥ 
               
               
                   
                   
               
             
            
               
                   
                 3 
                 18 
                 0.61 
                 0.35 
               
               
                   
                 4 
                 21 
                 0.61 
                 0.35 
               
               
                   
                 5 
                 23 
                 0.60 
                 0.35 
               
               
                   
                 6 
                 26 
                 0.60 
                 0.34 
               
               
                   
                 7 
                 30 
                 0.59 
                 0.34 
               
               
                   
                 8 
                 34 
                 0.58 
                 0.33 
               
               
                   
                 9 
                 39 
                 0.58 
                 0.32 
               
               
                   
                 Wedge 
                 44 
                 0.57 
                 0.32 
               
               
                   
                 Gap Wedge 
                 49 
                 0.56 
                 0.31 
               
               
                   
                 Sand Wedge 
                 54 
                 0.55 
                 0.30 
               
               
                   
                 Lob Wedge 
                 59 
                 0.55 
                 0.29 
               
               
                   
                   
               
            
           
         
       
     
     As discussed herein, golf club heads with different loft angles may have different internal cavity shapes, port locations, mass portion locations, filler material volumes, different CG locations, different size face portions, or different golf club head cross sectional shapes. In one example, a golf club head with a relatively higher loft angle may have a generally smaller cavity width profile than a golf club head with a lower loft angle. Accordingly, the value of V m /V c  for the golf club with the relatively higher loft angle may be generally smaller than the golf club head with the lower loft angle due to the difference in the amount of filler materials that may be provided in the interior cavities of each golf club head as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The values of the coefficients A 1 , A 2 , B 1 , and B 2  within the boundaries of these coefficients as defined herein may maintain a certain gap or a certain perimeter gap between the first filler material  1712  and the inner walls of the interior cavity  1510  as described herein, and/or optimize or maximize the width  1722  of the first filler material  1712  at or proximate to the ball strike region  1468 . Additionally, the values of the coefficients A 1 , A 2 , B 1 , and B 2  may vary within the boundaries of these coefficients as defined herein based on the specific internal configuration or structure of a golf club head. For example, as shown in  FIG.  22   , the widths of certain areas of the interior cavity  1510  may not be sufficiently large to include both the first filler material  1712  and the second filler material  1714 . As shown in  FIG.  19   , an area of the interior cavity  1510  between the port  352  and the face portion  1462  may only include the second filler material  1714 . Accordingly, the absence of first filler material  1712  in the area of the interior cavity  1510  between the port  352  and the face portion  1462  as shown in  FIG.  19    may affect both the upper boundary and the lower boundary of the ratio of the frontal area of the first filler material  1712  to the area of the inner surface portion  1469  of the face portion  1462  and/or the ratio of the volume of the first filler material  1712  to the volume of the interior cavity  1510 . In another example, as shown in  FIGS.  15  and  16   , the ratio of the frontal area  1713  of the first filler material  1712  to the area of the inner surface portion  1469  of the face portion  1462  and/or the ratio of the volume of the first filler material  1712  to the volume of the interior cavity  1510  may be determined so that the width of the first filler material  1712  at the ball strike region  1468  is maximized while still maintaining a gap  1724  of sufficient width to accommodate the second filler material  1714 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described herein, in one example, the first filler material  1712  may not be attached to the entire inner surface portion  1469  of the face portion  1462 . Accordingly, the first filler material  1712  and the perimeter edge portion  1461  (or the perimeter portion  1467  of the face portion) may be spaced apart by a perimeter gap  1725 . The perimeter gap  1725  may be greater than the gap  1724  due to one or more golf club head design and manufacturing considerations. For example, the perimeter gap  1725  may have to be sufficiently large so that the heat from any welding or soldering process as described herein to attach the perimeter portion  1467  of the face portion  1462  to the perimeter edge portion  1461  of the body portion  1410  does not damage, shift, move, detach from the face portion  1462 , and/or alter the material properties (e.g., melt) of the first filler material  1712  at or proximate to perimeter portion  1467  of the face portion  1462 . Accordingly, for example, as shown in  FIGS.  21  and  22   , the perimeter gap  1725  may be larger than the gap  1724 . In another example, as shown in  FIG.  22   , portions of the interior cavity  1510  at or proximate to the perimeter edge portion  1461  may not be sufficiently wide to include both the first filler material  1712  and the second filler material  1714 . Accordingly, the perimeter gap  1725  may be substantially greater than the gap  1724 . Thus, the gap  1724  may be configured such that the first filler material  1712  follows the contour of the inner walls  1512  of the interior cavity  1510 , whereas the perimeter gap  1725  may be similar, greater, or substantially greater than the gap  1725  depending on the location or region of the interior cavity  1510 . In one example, the relationship between the perimeter gap  1725  and the gap  1724  may be expressed by the following equation: 
     
       
         
           
             
               
                 
                   where 
                   : 
                   
                     
                       
                         
                           
                             
                               Wg 
                               PR 
                             
                             
                               Wg 
                               min 
                             
                           
                           ≥ 
                           1.38 
                         
                       
                     
                     
                       
                         
                           
                             
                               Wg 
                               PR 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             is 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             the 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             width 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             of 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             the 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             perimeter 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             gap 
                             ⁢ 
                             
                               
                                   
                               
                               ⁢ 
                               
                                   
                               
                             
                             ⁢ 
                             1725 
                           
                           , 
                           and 
                         
                       
                     
                     
                       
                         
                           
                             Wg 
                             min 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           is 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           the 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           minimum 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           width 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           of 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           the 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           gap 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1724. 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     In one example, the first filler material  1712  may include a polymer material having a relatively high coefficient of restitution (COR). The COR of the first filler material  1712  may be determined by shooting a golf ball sized sample of the first filler material  1712  from an air cannon toward a steel plate. Two light screens at known positions between the cannon and the plate may be used to measure the approach velocity and rebound velocities of the sample. The COR of the sample may then be calculated as the rebound velocity divided by the approach velocity. In one example, he first filler material  1712  may have a COR of greater than or equal to 0.7 at an approach velocity of 125 ft/s (51.1 m/s). In another example, the first filler material  1712  may have a COR of greater than or equal to 0.75 at an approach velocity of 125 ft/s (51.1 m/s). In yet another example, the first filler material  1712  may have a COR of greater than or equal to 0.7 and less than or equal to 0.9 at an approach velocity of 125 ft/s (51.1 m/s). The COR of any of the materials described herein, including any of the filler materials described herein, may be determined by the above-described method. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The compression of the golf ball sized sample may be related to the COR of the golf ball sized sample. Compression is a measurement of how much the golf ball sized sample deforms (compresses) under load. A relatively lower compression rating indicates a softer filler material, whereas a relatively higher compression rating indicates a firmer filler material. Compression may be measured by using an ATTI compression gauge, manufactured by ATTI Engineering, Union City, N.J. In one example, the COR of the first filler material  1712  may be greater than or equal to 0.75 at a compression of greater than or equal to 35. In another example, the COR of the first filler material  1712  may be greater than or equal to 0.78 at a compression of greater than or equal to 2 and less than or equal to 0.8 at a compression of less than or equal to 80. In yet another example, the COR of the first filler material  1712  may be greater than or equal to 0.78 at a compression of greater than or equal to 45 and less than or equal to 0.9 at a compression of less than or equal to 90. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the first filler material  1712  may be a polymer material having a density of greater than or equal to 1.1 g/cm 3  and less than or equal to 1.3 g/cm 3 . In another example, the first filler material  1712  may be a polymer material having a density of greater than or equal to 1.15 g/cm 3  and less than or equal to 1.38 g/cm 3 . In yet another example, the first filler material  1712  may be a polymer material having a density of greater than or equal to 1.1 g/cm 3  and less than or equal to 1.2 g/cm 3 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the first filler material  1712  may be a polymer material including rubber or a rubber compound similar to any of the rubber or rubber compounds described herein that may provide the COR and compression ranges described herein. In one example, the first filler material  1712  may include rubber and at least another compound that may provide increased softness or firmness to the first filler material  1712  to maximize the COR of the first filler material  1712  while maintaining compression values within a certain range as described herein. In one example, the first filler material  1712  may include rubber and Zinc Diacrylate (ZDA), which may increase the compression value of the first filler material  1712  and hence the COR of the first filler material  1712 . The amount of Zinc Diacrylate (ZDA) in the first filler material  1712  may be varied to achieve certain COR and/or compression values as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The adhesive for bonding the first filler material  1712  to the back surface  1466  of the face portion  1462  may be any type of adhesive that can bond the first filler material  1712  to the material of the face portion  1462 . In one example, the first filler material  1712  may be a rubber or a rubber compound and the face portion  1462  may be constructed from a steel-based material such as stainless steel. Accordingly, the adhesive for bonding the first filler material  1712  to the back surface  1466  of the face portion  1462  may be a type of adhesive used to bond steel-based materials to rubber or rubber compounds. In another example, the first filler material  1712  may be a rubber or a rubber compound and the face portion  1462  may be constructed from titanium or a titanium alloy. Accordingly, the adhesive for bonding the first filler material  1712  to the back surface  1466  of the face portion  1462  may be a type of adhesive used to bond titanium-based materials to rubber or rubber compounds. In yet another example, the first filler material  1712  may be bonded to the back surface  1466  of the face portion  1462  with the second filler material  1714 . The bonding of the first filler material  1712  to any portion of the body portion  1410 , the face portion  1462 , and/or the second filler material  1714 , and the bonding of the second filler material  1714  to the body portion  1410 , the face portion  1462 , and/or the first filler material  1712  may be similar to any of the bonding properties and procedures described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example (not shown), the interior cavity  1510  may be entirely filled with the first filler material  1712 . In another example, as shown in  FIGS.  14 - 24    and described herein, the interior cavity  1510  may be partially filled with the first filler material  1712  to define the gap  1724  between the first filler material  1712  and the inner walls  1512  of the interior cavity  1510 . Accordingly, the remaining portions of the first interior cavity  1510  may be filled with a second filler material  1714 . As described herein, the second filler material  1714  may provide or assist (e.g., alone or in conjunction with one or more adhesives) in the coupling of the first filler material  1712  with the face portion  1462 . In other words, the first filler material  1712  may be maintained against the back surface  1466  of the face portion  1462  by the second filler material  1714 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the second filler material  1714  may have one or more different properties than the first filler material  1712  such as density, compression, hardness (i.e., durometer), tensile strength, shear strength, viscosity, elasticity, etc., to optimize energy transfer from the face portion  1462  to a golf ball. The second filler material may be a polymer material such as an epoxy. In one example, the second filler material  1714  may have a lower COR than the first filler material  1712 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described herein, the first filler material  1712  and/or the second filler material  1714  may provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  1400  strikes a golf ball as perceived by an individual using the golf club head  1400 , provide structural support for the face portion  1462 , and/or improve ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The first filler material  1712 , the second filler material  1714 , or both may provide the properties and characteristics described herein whereas the mass of the first filler material  1712 , the mass of the second filler material  1714 , or the masses of both relative to the mass of the body portion  1410  may optimally affect the mass, mass distribution, CG, MOI characteristics, structural integrity and/or or other static and/or dynamic characteristics of the golf club head  1400 . In one example, a relationship between the mass of the first filler material  1712  (m m1 ), the mass of the second filler material  1714  (m m2 ), and the mass of the body portion  1410  (m b ) may be expressed by the following equation:
 
 m   m1   =m   b ( C   1   α+C   2 )− m   m2   (5)
         where:
           m m1  is the mass of the first filler material  1712 ,   m m2  is the mass of the second filler material  1714 ,   m b  is the mass of the body portion  1410 ,   α is the loft angle,   −0.001≤C 1 ≤0.001, and   0.1≤C 2 ≤0.2.   
               

     The upper and lower values of the coefficients C 1  and C 2  as defined herein may provide the upper and lower boundaries of a ratio of the sum of the masses of the first filler material  1712  and the second filler material  1714  to the mass of the body portion  1410  (i.e., (m m1 +m m2 )/m b ). In one example, according to Equation (5) and assuming a value of −0.0016 for the coefficient C 1 , upper and lower boundaries of a ratio of the sum of the masses of the first filler material  1712  and the second filler material  1714  to the mass of the body portion  1410  for a set of iron-type golf club heads may be determined as shown in Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                   
                 (m m1  + 
                 (m m1  + 
               
               
                   
                 Iron-Type 
                 α 
                 m m2 )/m b )≤ 
                 m m2 )/m b )≥ 
               
               
                   
                   
               
             
            
               
                   
                 3 
                 18 
                 0.16 
                 0.08 
               
               
                   
                 4 
                 21 
                 0.16 
                 0.08 
               
               
                   
                 5 
                 23 
                 0.15 
                 0.08 
               
               
                   
                 6 
                 26 
                 0.15 
                 0.07 
               
               
                   
                 7 
                 30 
                 0.14 
                 0.06 
               
               
                   
                 8 
                 34 
                 0.13 
                 0.06 
               
               
                   
                 9 
                 39 
                 0.13 
                 0.05 
               
               
                   
                 Wedge 
                 44 
                 0.12 
                 0.04 
               
               
                   
                 Gap Wedge 
                 49 
                 0.11 
                 0.03 
               
               
                   
                 Sand Wedge 
                 54 
                 0.10 
                 0.03 
               
               
                   
                 Lob Wedge 
                 59 
                 0.09 
                 0.02 
               
               
                   
                   
               
            
           
         
       
     
     The values of the coefficients C 1  and C 2  within the boundaries of these coefficients as defined herein may (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  1400  strikes a golf ball as perceived by an individual using the golf club head  1400 ), (ii) provide structural support for the face portion  1462 , and/or (iii) improve ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The first filler material  1712  and the second filler material  1714  may provide the properties and characteristics described herein whereas the mass of the first filler material  1712  and the second filler material  1714  relative to the mass of the body portion  1410  optimally affect the mass, mass distribution, CG, MOI characteristics, structural integrity and/or or other static and/or dynamic characteristics of the golf club head  1400 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
       FIG.  25    depicts one manner by which the example golf club head  1400  as described herein may be manufactured. In the example of  FIG.  25   , the process  2500  may begin with providing a body portion  1410  and a face portion  1462  of a golf club head  1400  (block  2510 ). The first filler material  1712  may be formed or molded into a certain shape (block  2512 ) as described in detail herein, for example, to resemble, closely resemble, or generally resemble the contour of the interior cavity  1510  (i.e., the shape of the inner walls  1512  of the interior cavity  1510 ) of the golf club head  1400 . The first filler material  1712  in the molded form may then be attached or bonded to the back surface  1466  of the face portion  1462  (block  2514 ) as described herein. The face portion  1462  may then be attached to the body portion  1410  as described herein to form or enclose the interior cavity  1510  (block  2516 ). The second filler material  1714  may then be injected into the interior cavity  1510  through one or more of the ports of the first set of ports  350 , the second set of ports  360 , and/or the third set of ports  370  that may be connected to the interior cavity  1510  as described herein to fill the gap  1724 , to fill the remaining portions of the interior cavity  1510  (block  2518 ), and/or to surround the first filler material  1712 . The second filler material  1714  may be injected into the interior cavity  1510  at a relatively high pressure if necessary and/or from more than one port if necessary, to allow the second filler material  1714  to fill relatively narrow gaps  1724  at certain locations in the interior cavity  1510  as described herein between the first filler material  1712  and the inner walls of the interior cavity  1510 . The second filler material  1714  may then cure at ambient temperature or by one or more heating/cooling cycles depending on the material used for the second filler material  1714 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  26 - 28   , a golf club head  2600  may include a body portion  2610  having a toe portion  2640 , a heel portion  2650 , a front portion  2660  with a face portion  2662  (e.g., a strike face) having a front surface  2664  and a back surface  2666 , a back portion  2670 , a top portion  2680 , and a sole portion  2690 . In one example, the body portion  2610  may be a hollow body including the interior cavity  2677  extending between the front portion  2660  and the back portion  2670  and extending between the top portion  2680  and the sole portion  2690 . The golf club head  2600  may be similar in many respects to any of the golf club heads described herein. For example, the golf club head  2600  may include any number of ports and/or mass portions similar to any of the golf club head described herein. In another example, the golf club head  2600  may include any of the materials described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  2600  may include one or more filler materials in the interior cavity  2677 . In one example, as shown in  FIGS.  26 - 28   , the golf club head  2600  may include a first filler material  2711  and a second filler material  2713  having one or more different properties than the first filler material  2711  (e.g., elasticity, density, hardness, etc.). In one example, the first filler material  2711  may be a polymer material having a different elasticity than the second filler material  2713  (e.g., the second filler material  2713  may be more elastic than the first filler material  2711  or vice versa). In another example, the first filler material  2711  may include a polymer material having a different density than the second filler material  2713  (e.g., the first filler material  2711  may have a higher density than the second filler material  2713  or vice versa). In yet another example, the first filler material  2711  may have a different hardness (e.g., Shore D hardness or Shore A hardness) than the second filler material  2713  (e.g., the first filler material  2711  may have a relatively higher hardness than the second filler material  2713  or vice versa). In yet another example, the first filler material  2711  and the second filler material  2713  may have different coefficients of restitution (COR). The first and second filler materials  2711  and  2713 , respectively, may be different types of non-metal materials. In one example, the first filler material  2711  may include a thermoset material whereas the second filler material  2713  may include a thermoplastic elastomer material. In another example, the first filler material  2711  may be a rubber or a rubber compound as described herein. In another example, the second filler material  2713  may include a thermoset material whereas the first filler material  2711  may include a thermoplastic elastomer material. The first and second filler materials  2711  and  2713 , respectively, may include the same type of non-metal material but different properties. In one example, the first filler material  2711  may include a thermoset material and the second filler material  2713  may include a thermoset material having a different elasticity than the first filler material  2711 . In another example, the first filler material  2711  may include a thermoplastic material and the second filler material  2713  may include a thermoplastic material having a different elasticity than the first filler material  2711 . Alternatively, the first and second filler materials  2711  and  2713 , respectively, may include metal materials and/or non-metal materials. For example, the first filler material  2711  may include one or more metal-based materials whereas the second filler material  2713  may include one or more polymer materials. Further, the first filler material  2711  and/or the second filler material  2713  may include any of the filler materials described herein. In one example, the first filler material  2711  may be an epoxy material such as any of the epoxy materials described herein and the second filler material  2713  may be an elastomer material such as any of the elastomer materials described herein. In one example, the first filler material  2711  may be an epoxy material such as any of the epoxy materials described herein and the second filler material  2713  may be an elastomer material such as any of the elastomer materials described herein. In yet another example, the first filler material  2711  may be a rubber-based compound and the second filler material  2713  may be an epoxy-based compound. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIGS.  26 - 28   , the first filler material  2711  may be attached or bonded to a portion of the back surface  2666  of the face portion  2662 . In one example, the first filler material  2711  may be attached or bonded to a ball strike region of the back surface  2666  of the face portion  2662 . In another example, the first filler material  2711  may be attached or bonded to the ball strike region of the back surface  2666  of the face portion  2662  and an area surrounding the ball strike region of the back surface  2666  of the face portion  2662 . In one example, the width of the first filler material  2711  (i.e., the thickness of the first filler material  2711 ) may be less than the thickness of the face portion  2662 . In another example, the width of the first filler material  2711  may be similar to the thickness of the face portion  2662 . In yet another example, the width of the first filler material  2711  may be greater than the thickness of the face portion  2662 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIGS.  26 - 28   , the remaining portions of the interior cavity  2677  may be partially or entirely filled with the second filler material  2713 . The first filler material  2711  may be surrounded by the second filler material  2713  such that the second filler material  2713  is attached or bonded to the remaining portions of the back surface  2666  of the face portion  2662 . As shown in  FIG.  26   , the second filler material  2633  may be attached or bonded to the back surface  2666  of the face portion  2662  and define a perimeter portion on the back surface  2666  of the face portion  2662  surrounding the first filler material  2711 . For example, as shown in  FIGS.  26 - 28   , the second filler material  2713  may be attached or bonded to a portion of the back surface  2666  of the face portion  2662  and surround the first filler material  2711  at or proximate to the toe portion  2640 , attached or bonded to a portion of the back surface  2666  of the face portion  2662  and surround the first filler material  2711  at or proximate to the heel portion  2650 , attached or bonded to a portion of the back surface  2666  of the face portion  2662  and surround the first filler material  2711  at or proximate to the top portion  2680 , and/or attached or bonded to a portion of the back surface  2666  of the face portion  2662  and surround the first filler material  2711  at or proximate to the sole portion  2690 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  29 - 31   , a golf club head  2900  may include a body portion  2910  having a toe portion  2940 , a heel portion  2950 , a front portion  2960  with a face portion  2962  (e.g., a strike face) having a front surface  2964  and a back surface  2966 , a back portion  2970 , a top portion  2980 , and a sole portion  2990 . In one example, the body portion  2910  may be a hollow body including the interior cavity  2977  extending between the front portion  2960  and the back portion  2970  and extending between the top portion  2980  and the sole portion  2990 . The golf club head  2900  may be similar in many respects to any of the golf club heads described herein. For example, the golf club head  2900  may include any number of ports and/or mass portions similar to any of the golf club head described herein. In another example, the golf club head  2900  may include any of the materials described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  2900  may include a first filler material  3011  and a second filler material  3013  that may be similar to the first filler material  2711  and the second filler material  2713 , respectively, of the golf club head  2600 . In the example of  FIGS.  29 - 31   , the first filler material  3011  may be attached or bonded to a portion of the back surface  2966  of the face portion  2962  similar to the examples of  FIGS.  26 - 28   . In the example of  FIGS.  29 - 31   , however, the first filler material  3011  may extend from the back surface  2966  of the face portion  2962  to a back surface  2976  of a back wall  2972  of the back portion  2970 . The first filler material  3011  may contact or be attached or bonded to the back surface  2976  of a back wall  2972  of the back portion  2970 . The remaining portions of the interior cavity  2977  may be partially or entirely filled with the second filler material  3013 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  32 - 34   , a golf club head  3200  may include a body portion  3210  having a toe portion  3240 , a heel portion  3250 , a front portion  3260  with a face portion  3262  (e.g., a strike face) having a front surface  3264  and a back surface  3266 , a back portion  3270 , a top portion  3280 , and a sole portion  3290 . In one example, the body portion  3210  may be a hollow body including the interior cavity  3277  extending between the front portion  3260  and the back portion  3270  and extending between the top portion  3280  and the sole portion  3290 . The golf club head  3200  may be similar in many respects to any of the golf club heads described herein. For example, the golf club head  3200  may include any number of ports and/or mass portions similar to any of the golf club head described herein. In another example, the golf club head  3200  may include any of the materials described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  3200  may include a first filler material  3311  and a second filler material  3313  that may be similar to the first filler material  2711  and the second filler material  2713 , respectively, of the golf club head  2600 . In the example of  FIGS.  32 - 34   , the first filler material  3311  may be attached or bonded to a substantial portion of or the entire back surface  3266  of the face portion  3262 . In one example, the width of the first filler material  3311  (i.e., the thickness of the first filler material  3311 ) may be less than the thickness of the face portion  3262 . In another example, the width of the first filler material  3311  may be similar to the thickness of the face portion  3262 . In yet another example, the width of the first filler material  3311  may be greater than the thickness of the face portion  3262 . The remaining portions of the interior cavity  3277  may be partially or entirely filled with the second filler material  3313 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  35 - 37   , a golf club head  3500  may include a body portion  3510  having a toe portion  3540 , a heel portion  3550 , a front portion  3560  with a face portion  3562  (e.g., a strike face) having a front surface  3564  and a back surface  3566 , a back portion  3570 , a top portion  3580 , and a sole portion  3590 . In one example, the body portion  3510  may be a hollow body including the interior cavity  3577  extending between the front portion  3560  and the back portion  3570  and extending between the top portion  3580  and the sole portion  3590 . The golf club head  3500  may be similar in many respects to any of the golf club heads described herein. For example, the golf club head  3500  may include any number of ports and/or mass portions similar to any of the golf club head described herein. In another example, the golf club head  3500  may include any of the materials described herein. The golf club head  3500  may include a first filler material  3611  and a second filler material  3613  that may be similar to the first filler material  2711  and the second filler material  2713 , respectively, of the golf club head  2600 . In the example of  FIGS.  35 - 37   , a portion of the interior cavity  3577  above a horizontal midplane  3583  of the body portion  3510  may be partially or entirely filled with the first filler material  3611 , and a portion of the interior cavity  3577  below the horizontal midplane  3583  may be partially or entirely filled with the second filler material  3613 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  38 - 40   , a golf club head  3800  may include a body portion  3810  having a toe portion  3840 , a heel portion  3850 , a front portion  3860  with a face portion  3862  (e.g., a strike face) having a front surface  3864  and a back surface  3866 , a back portion  3870 , a top portion  3880 , and a sole portion  3890 . In one example, the body portion  3810  may be a hollow body including the interior cavity  3877  extending between the front portion  3860  and the back portion  3870  and extending between the top portion  3880  and the sole portion  3890 . The golf club head  3800  may be similar in many respects to any of the golf club heads described herein. For example, the golf club head  3800  may include any number of ports and/or mass portions similar to any of the golf club head described herein. In another example, the golf club head  3800  may include any of the materials described herein. The golf club head  3800  may include a first filler material  3911  and a second filler material  3913  that may be similar to the first filler material  2711  and the second filler material  2713 , respectively, of the golf club head  2600 . In the example of  FIGS.  38 - 40   , a portion of the interior cavity  3877  below a horizontal midplane  3883  of the body portion  3810  may be partially or entirely filled with the first filler material  3911 , and a portion of the interior cavity  3877  above the horizontal midplane  3883  may be partially or entirely filled with the second filler material  3913 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  41 - 43   , a golf club head  4100  may include a body portion  4110  having a toe portion  4140 , a heel portion  4150 , a front portion  4160  with a face portion  4162  (e.g., a strike face) having a front surface  4164  and a back surface  4166 , a back portion  4170 , a top portion  4180 , and a sole portion  4190 . In one example, the body portion  4110  may be a hollow body including the interior cavity  4177  extending between the front portion  4160  and the back portion  4170  and extending between the top portion  4180  and the sole portion  4190 . The golf club head  4100  may be similar in many respects to any of the golf club heads described herein. For example, the golf club head  4100  may include any number of ports and/or mass portions similar to any of the golf club head described herein. In another example, the golf club head  4100  may include any of the materials described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  4100  may include a first filler material  4211  and a second filler material  4213  that may be similar to the first filler material  2711  and the second filler material  2713 , respectively, of the golf club head  2600 . In the example of  FIGS.  41 - 43   , a portion of the interior cavity  4177  spaced apart from any boundary of the interior cavity  4177  defined by the body portion  4110  and the face portion  4162  may be filled with the first filler material  4211 , and the remaining portions of the interior cavity  4177  may be partially or entirely filled with the second filler material  4213 . In other words, the first filler material  4211  may be suspended in the interior cavity  4177  and entirely surrounded by the second filler material  4213 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as described herein, one or more polymer materials may be injection molded in the body portion of any of the golf club heads described herein. The one or more polymer materials may be made or formed by any useful forming means for forming polymers. This include, molding including compression molding, injection molding, blow molding, and transfer molding; film blowing or casting; extrusion, and thermoforming; as well as by lamination, pultrusion, protrusion, draw reduction, rotational molding, spin bonding, melt spinning, melt blowing; or combinations thereof. In another example, any one or more of the polymer materials described herein may be in pellet or solid pieces that may be placed in the interior cavity and expanded and/or cured with heat. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity of any of the golf club heads described herein may be partially (i.e., greater than 0% and less than 100%) or entirely filled with one or more thermoset materials (e.g., one or more epoxy materials), such as any one or more of the epoxy materials described herein or any other suitable epoxy material(s). In one example, the mass of the thermoset material (e.g., epoxy) partially, substantially (e.g., filling at least 50% of the interior cavity), or entirely filling the interior cavity of any of the golf club heads described herein may be greater than or equal to 6.0 grams and less than or equal to 32.0 grams. A thermoset material partially, substantially, or entirely filling the interior cavity may affect vibration and noise dampening, structural support for a relatively thin face portion, ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As illustrated in  FIG.  44   , for example, the interior cavity  4412  of a body portion  4410  of the golf club head  4400 , which may be similar to any of the golf club heads described herein, may be filled with a thermoset material  4414  (e.g., epoxy material) below the horizontal midplane  4470  of the golf club head  4400 . In another example, the interior cavity  4412  of the golf club head  4400  or any of the golf club heads described herein may be filled with a thermoset material (e.g., epoxy material) above the horizontal midplane  4470  (not shown). In yet another example, the interior cavity  4412  of the golf club head  4400  or any of the golf club heads described herein may be filled with a thermoset material (e.g., epoxy material) above and below the horizontal midplane  4470  and yet have regions in the interior cavity  4412  that may not include any thermoset materials or include other materials (not shown). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As shown in  FIG.  45   , for example, a golf club head  4500 , which may be similar to any of the golf club heads described herein, may include a body portion  4510  with an interior cavity  4512  having a width  4516  of a thermoset material  4514 . The width  4516  may be related to face portion thickness  4519  of the face portion  4518  by the following expression:
 
 W   th   =aT   f   (6)
         Where: 0.5≤a≤5.0
           W th  is the width of the thermoset material in inches, and   T f  is the thickness of the face portion in inches.   
               

     In one example, the width  4516  of the thermoset material  4514  may be greater than or equal to half the face portion thickness  4519 . In another example, the width  4516  of the thermoset material  4514  may be greater than or equal to the face portion thickness  4519  (e.g., W th ≥T f ). In yet another example, the width  4516  of the thermoset material  4514  may be greater than or equal to twice the face portion thickness  4519  (e.g., W th ≥2T f ). In another example, the width  4516  of the thermoset material  4514  may be greater than or equal to three times the face portion thickness  4519  (e.g., W th ≥3T f ). In yet another example, the width  4516  of the thermoset material  4514  may be greater than five times the face portion thickness  4519  (e.g., W th ≥5T f ). In yet another example, the width  4516  of the thermoset material  4514  may be greater than or equal to the face portion thickness  4519  and less than or equal to three times the face portion thickness  4519  (e.g., T f ≤W th ≤3T f ). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, for any of the golf club heads described herein, the mass of a thermoset material partially, substantially, or entirely filling the interior cavity may be related to the mass of the golf club head by the following expression: 
     
       
         
           
             
               
                 
                   where 
                   : 
                   
                     
                       
                         
                           0.03 
                           ≤ 
                           
                             
                               m 
                               T 
                             
                             
                               m 
                               H 
                             
                           
                           ≤ 
                           0.2 
                         
                       
                     
                     
                       
                         
                           
                             
                               m 
                               T 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             is 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             the 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             mass 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             of 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             the 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             thermoset 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             material 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             in 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             grams 
                           
                           , 
                           and 
                         
                       
                     
                     
                       
                         
                           
                             m 
                             H 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           is 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           the 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           mass 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           of 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           the 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           golf 
                           ⁢ 
                           
                             
                                 
                             
                             ⁢ 
                             
                                 
                             
                           
                           ⁢ 
                           club 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           head 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           in 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             grams 
                             . 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     According to the above equation, a ratio of the mass of the thermoset material and the mass of the golf club head may be greater than or equal to 0.03 and less than or equal to 0.2. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     A thermoset material partially, substantially, or entirely filling the interior cavity may have a certain Shore D hardness to provide vibration and noise dampening and/or structurally support a relatively thin face portion of a golf club head. In one example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a Shore D hardness of at least 45. In another example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a Shore D hardness of greater than or equal to 45 and less than or equal to 80. In another example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a Shore D hardness of greater than or equal to 50 and less than or equal to 70. In yet another example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a Shore D hardness of greater than or equal to 55 and less than or equal to 65. In yet another example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a Shore D hardness of greater than or equal to 55 and less than or equal to 75. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     A thermoset material partially, substantially, or entirely filling the interior cavity may have a certain density to provide vibration and noise dampening and/or structurally support a relatively thin face portion of a golf club head. In one example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a density of greater than or equal to 1.0 grams per cubic centimeter (g/cm 3 ) and less than or equal to 2.0 g/cm 3 . In another example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a density of greater than or equal to 1.1 g/cm 3  and less than or equal to 1.5 g/cm 3 . In yet another example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a density of greater than or equal to 1.0 g/cm 3  and less than or equal to 1.4 g/cm 3 . In yet another example, a thermoset material partially, substantially, or entirely filling the interior cavity may have a density of greater than or equal to 1.1 g/cm 3  and less than or equal to 1.2 g/cm 3 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The polymer material (e.g., the thermoset material  4514  as shown in  FIG.  45   ) may be located adjacent to the back surface  4521  of the face portion  4518 . For example, the thermoset material  4514  may be attached and/or bonded directly to the back surface  4521  of the face portion  4518 . Alternatively, the thermoset material  4514  may be located away from the face portion  4518 . In one example, the thermoset material  4514  be attached and/or bonded to the back-wall portion  4575  of the back portion  4574 . As a result, the thermoset material  4514  may not be in contact with the back surface  4521  of the face portion  4518 . While the examples herein describe a polymer material such as the thermoset material  4514  being attached and/or bonded to various surfaces and/or wall portions of the golf club head  4500 , or suspended in the interior cavity  4512 , the thermoset material  4514  may be attached and/or bonded to more or less surfaces and/or wall portions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As shown in  FIG.  46   , for example, a golf club head  4600 , which may be similar to any of the golf club heads described herein, may have a body portion  4610  include an internal cavity  4612  having an internal cavity width that may vary between the top portion  4680  and the sole portion  4690 . In particular, the internal cavity  4612  may include a first width  4620  (W 1 ) above a horizontal midplane  4670  of the golf club head  4600 , a second width  4630  (W 2 ) below the horizontal midplane  4670 , and a third width  4640  (W 3 ) between the first width  4620  and the second width  4630 . The third width  4640  may be at or below the horizontal midplane  4670 . In one example, the third width  4640  may be above one or more ports (e.g., one generally shown as  4622 ). Accordingly, the third width  4640  may be located above one or more mass portions (not shown in  FIG.  46    but for example, a mass portion disposed in the port  4622 ) and/or be closer to the horizontal midplane  4670  than one or more mass portions. In another example, the third width  4640  may be above one or more ports of the golf club head  4500  and below the horizontal midplane  4670 . The third width  4640  may be greater than the first width  4620  (e.g., W 3 &gt;W 1 ) and greater than the second width  4630  (e.g., W 3 &gt;W 2 ). In one example, the first width  4620  may be greater than or equal to the second width  4630  (e.g., W 2 ≥W 1 ). In another example, the second width  4630  may be greater than or equal to the first width  4620  (e.g., W 1 ≥W 2 ). In yet another example, the third width  4640  may be no more than three times the second width  4630 . In yet another example, the third width  4640  may be no more than twice the second width  4630 . In yet another example, the third width  4640  may be no more than 1.5 times the second width  4630 . In yet another example, the third width  4640  may be no more than 1.38 times the second width  4630 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third width  4640  may be at a certain vertical location of the body portion  4610 . The face portion  4618  of the golf club head  4600  may include a plurality of grooves. The face portion  4618  of the golf club head  4600  may include a similar number of grooves as the golf club head  100  of  FIG.  1   . Accordingly, the face portion  4618  may include a plurality of grooves (e.g., eleven grooves are generally shown as grooves  4651 ,  4652 ,  4653 ,  4654 ,  4655 ,  4656 ,  4657 ,  4657 ,  4659 ,  4660 , and  4661  in  FIG.  46   ). The third width  4640  may be located between any of the plurality of grooves. In one example, the third width  4640  may be located between the first groove  4651  and the eleventh groove  4661  from the sole portion  4690 . In another example, the third width  4640  may be located between the fourth groove  4654  and the eighth groove  4658  from the sole portion  4690 . In yet another example, the third width  4640  may be located between the fifth groove  4655  and the seventh groove  4657  from the sole portion  4690 . Although  FIG.  46    may depict the first, second, and third widths  4620 ,  4630 , and  4640 , respectively, of the internal cavity  4612  relative to the loft plane (e.g., one generally shown as  1040  in  FIG.  3   ) associated with the face portion  4618  (e.g., normal to the loft plane), one or more widths may be measured relative to the ground plane (e.g., one generally shown as  1010  in  FIG.  1   ). For example, one or more widths of the internal cavity  4612  may be substantially parallel to the ground plane (e.g., one generally shown as  1010  in  FIG.  1   ). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the process of filling the interior cavity of the golf club head may not include applying a bonding portion to the back surface of the face portion. For example, as shown in  FIG.  47   , the process  4700  of filling the interior cavity of the golf club head may include partially, substantially, or entirely filling the interior cavity with an epoxy material (block  4710 ), and then curing the epoxy material (block  4720 ). The epoxy material may be injected into the interior cavity from one or more ports on the body portion of a golf club head as described herein. In one example, the process of curing the epoxy material may include using heat, radiation, and/or pressure for a certain period of time. In another example, the process of curing the epoxy material may only include allowing the epoxy material to cure at ambient or room temperature for a certain period of time. In another example, the process of filling the interior cavity of the golf club head may include applying a first epoxy material to the back surface of the face portion, curing the first epoxy material to a first cure state as described herein, filling the interior cavity with a second epoxy material that may be the same as or different from the first epoxy material, and curing the first epoxy material to the second cure state and curing the second epoxy material as described herein. In another example, more than two epoxy materials can be used to substantially or fully fill the interior cavity with single or multiple curing processes used for each epoxy material. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  48 - 53   , a golf club head  4800  may include a body portion  4810  having a toe portion  4840  with a toe portion edge  4842 , a heel portion  4850  with a heel portion edge  4852  that may include a hosel portion  4855  configured to receive a shaft (for example the shaft  9504 ) with a grip (for example the grip  9506 ) on one end and the golf club head  4800  on the opposite end of the shaft to form a golf club, a front portion  4860  with a perimeter edge portion  4861 , a back portion  4870  with a back wall portion  4872 , a top portion  4880  with a top portion edge  4882 , and a sole portion  4890  with a sole portion edge  4892 . The toe portion  4840 , the heel portion  4850 , the front portion  4860 , the back portion  4870 , the top portion  4880 , and/or the sole portion  4890  may partially overlap each other. The toe portion edge  4842 , the heel portion edge  4852 , the top portion edge  4882 , and the sole portion edge  4892  may define a periphery of the body portion  4810 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  4800  may be an iron-type golf club head (e.g., a 1-iron, a 2-iron, a 3-iron, a 4-iron, a 5-iron, a 6-iron, a 7-iron, an 8-iron, a 9-iron, etc.), or a wedge-type golf club head (e.g., a pitching wedge, a lob wedge, a sand wedge, an n-degree wedge such as 44 degrees (°), 48°, 52°, 56°, 60°, etc.). Although FIGS.  48 - 53  may depict a particular type of club head, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of club heads (e.g., a driver-type club head, a fairway wood-type club head, a hybrid-type club head, a putter-type club head, etc.). The volume of the golf club head  4800 , the materials of construction of the golf club head  4800 , and/or any components thereof may be similar to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  4800  may include a face portion  4862  (i.e., the strike face), which may be integrally formed with the body portion  4810  (e.g., a single unitary piece). In one example, as shown in  FIGS.  48 - 53   , the face portion  4862  may be a separate piece coupled (e.g., adhesively, mechanically, by welding, and/or by soldering) to the front portion  4860 . The face portion  4862  may include a front surface  4864  and a back surface  4866 . In one example (not shown), the front portion  4860  may include one or a plurality of recessed shoulders configured to receive the face portion  4862  for attachment of the face portion  4862  to the body portion  4810 . In another example, as shown in  FIGS.  48 - 53   , the back surface  4866  may include a perimeter portion  4867  that may be attached to a perimeter edge portion  4861  of the body portion  4810 . The perimeter portion  4867  of the face portion  4862  may be attached to the perimeter edge portion  4861  of the body portion  4810  by one or more fasteners, one or more adhesive or bonding agents, and/or welding or soldering. In one example, as shown in  FIGS.  48 - 53   , the perimeter portion  4867  of the face portion  4862  may be welded to the perimeter edge portion  4861  of the body portion  4810  at one or more locations. Alternatively, the entire perimeter portion  4867  of the face portion  4862  may be welded to the entire perimeter edge portion  4861  of the body portion  4810  (i.e., a continuous weld). The face portion  4862  may include a ball strike region  4868  to strike a golf ball. In one example, the center of the ball strike region  4868  may be a geometric center  4863  of the face portion  4862 . In another example, the geometric center  4863  of the face portion  4862  may be offset from a center of the ball strike region  4868 . In one example, the geometric center  4843  and one or more regions near and/or surrounding the geometric center within the ball strike region  4868  may provide a generally optimum location (i.e., optimum ball distance, ball speed, ball spin characteristics, etc.) on the face portion  4862  for striking a golf ball. In yet another example, any location at or near the geometric center  4863  and within the ball strike region  4868  may provide a generally optimum location on the face portion  4862  for striking a golf ball. However, a ball may be struck with any portion of the face portion  4862  within the ball strike region  4868  or outside the ball strike region  4868  for any of the golf club heads described herein resulting in certain ball flight characteristics different from an on-center hit that may be preferred by an individual. The configuration of the face portion  4862  and the attachment of the face portion  4862  (e.g., welding) to the body portion  4810  may be similar in many respects to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  4800  may be associated with a ground plane  5110 , a horizontal midplane  5120 , and a top plane  5130 . In particular, the ground plane  5110  may be a plane that is parallel or substantially parallel to the ground and is tangent to the lowest portion of the sole portion edge  4892  when the golf club head  4800  is at an address position (e.g., the golf club head  4800  aligned to strike a golf ball). A top plane  5130  may be a plane that is tangent to the upper most portion of top portion edge  4882  when the golf club head  4800  is at the address position. The ground and top planes  5110  and  5130 , respectively, may be parallel or substantially parallel to each other. The horizontal midplane  5120  may be vertically halfway between the ground and top planes  5110  and  5130 , respectively. Further, the golf club head  4800  may be associated with a loft plane  5140  defining a loft angle  5145  (α) of the golf club head  4800 . The loft plane  5140  may be a plane that is tangent to the face portion  4862 . The loft angle  5145  may be defined by an angle between the loft plane  5140  and a vertical plane  5150  normal to the ground plane  5110 . 
     The body portion  4810  may be a hollow body including an interior cavity  4910  having inner walls  4912 . The interior cavity  4910  may extend between the front portion  4860 , the back portion  4870 , the top portion  4880 , and the sole portion  4890 . In the example of  FIGS.  48 - 53   , the interior cavity  4910  of the body portion  4810  may be enclosed with and partially defined with the face portion  4862 . The configuration of the interior cavity  4910  (e.g., height, width, volume, shape, etc.), the configuration of the interior cavity  4910  relative to the body portion  4810  (e.g., volume of the interior cavity  4910  relative to the volume of body portion  4810 ), the width and height variation of the interior cavity  4910 , and access to the interior cavity  4910  from one or more ports on the body portion  4810  may be similar to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The back wall portion  4872  of the back portion  4870  may include an upper back wall portion  5212  and a lower back wall portion  5214 . The back wall portion  4872  may include a ledge portion  5216  that may extend between the toe portion edge  4842  and the heel portion edge  4852  in a continuous or discontinuous manner. The lower back wall portion  5214  may be located farther back on the body portion  4810  than the upper back wall portion  5212 , with the ledge portion  5216  defining a transition portion between the upper back wall portion  5212  and the lower back wall portion  5214 . Accordingly, the ledge portion  5216  may extend transverse to the upper back wall portion  5212  and the lower back wall portion  5214 . In one example, as shown in  FIGS.  48 - 53   , the ledge portion  5216  may include a first ledge portion  5226  and a second ledge portion  5236 . The first ledge portion  5226  may extend on the back wall portion from the toe portion edge  4842  to a back wall center portion  5240  of the back wall portion  4872 . The second ledge portion  5236  may extend from the center portion  5240  of the back wall portion  4872  to the heel portion edge  4852 . As shown in  FIGS.  48 - 53   , the ledge portion  5216  may provide for a relatively greater mass below the horizontal midplane  5120  and the mass of the body portion  4810  below the horizontal midplane  5120  to be moved farther back on the body portion  4810 . The width of the ledge portion  5216  may be greater than, equal to, or less than the width of the interior cavity at certain locations of the body portion  4810 . The configuration of the ledge portion  5216  (e.g., width, segments, tapering, shape, etc.) and the properties of the ledge portion  5216  relative to the width of the interior cavity may be similar to any ledge portion or similar structure of any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  4810  may include one or more ports, which may be exterior ports and/or interior ports (e.g., located inside the body portion  4810 ). The inner walls  4912  of the interior cavity  4910  may include one or more ports (not shown). In one example, as shown in  FIGS.  48 - 53   , the back portion  4870  may include one or more ports along or proximate to a periphery of the body portion  4810 . For example, the body portion  4810  may include a first set of ports  4920  (e.g., shown as ports  4921  and  4922 ), a second set of ports  4930  (e.g., shown as ports  4931  and  4932 ), a third set of ports  4940  (e.g., shown as ports  4941 ,  4942 , and  4943 ), and a fourth set of ports  4950  (e.g., shown as ports  4951  and  4952 ). The locations, spacing relative to other ports, and any other configuration of each port of the first set of ports  4920 , the second set of ports  4930 , the third set of ports  4940 , and/or the fourth set of ports  4950  may be similar in many respects to any of the ports described herein or described in any of the incorporated by reference applications. Further, any one or more of the ports of the first set of ports  4920 , the second set of ports  4930 , the third set of ports  4940 , and/or the fourth set of ports  4950  may be connected to interior cavity  4910  through which one or more filler materials may be injected into the interior cavity  4910 . In the example of  FIGS.  48 - 53   , the ports  4921 ,  4931 , and  4951  may be connected to the interior cavity  4910  via openings  4961 ,  4971 , and  4981 , respectively. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Each port of the first set of ports  4920  may be separated by a distance less than the port diameter of any of the ports of the first set of ports  4920 . Each port of the second set of ports  4930  may be separated by a distance less than the port diameter of any of the ports of the second set of ports  4930 . Each port of the third set of ports third set of ports  4940  may be separated by a distance less than the port diameter of any of the ports of the third set of ports  4940 . Each port of the fourth set of ports  4950  may be separated by a distance less than the port diameter of any of the ports of the third set of ports  4950 . In one example, the first set of ports  4920  and the second set of ports  4930  may be spaced apart by a distance greater than the port diameter of any of the ports of the first set of ports  4920  and the second set of ports  4930 . In another example, the second set of ports  4930  and the third set of ports  4940  may be spaced apart by a distance greater than the port diameter of any of the ports of the second set of ports  4930  and the third set of ports  4940 . In yet another example, the third set of ports  4940  and the fourth set of ports  4945  may be spaced apart by a distance greater than the port diameter of any of the ports of the third set of ports  4940  and the fourth set of ports  4950 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Although the figures may depict the ports as separate and individual parts, each set or a combination of adjacent sets of ports of the first, second, third, and fourth sets of ports  4920 ,  4930 ,  4940 , and  4950 , respectively, may be a single port. In one example, all ports of the first set of ports  4920  may be combined into a single port (e.g., a first port). In another example, all ports of the second set of ports  4930  may be combined into a single port (e.g., a second port). In another example, all ports of the third set of ports  4940  may be combined into a single port (e.g., a third port). In yet another example, all ports of the fourth set of ports  4950  may be combined into a single port (e.g., a fourth port). While the figures may depict a particular number of ports, the apparatus, methods, and articles of manufacture described herein may include more or a smaller number of ports. 
     The body portion  4810  may include one or more mass portions (e.g., weight portion(s)), which may be integral mass portion(s) or separate mass portion(s) that may be coupled to the body portion  4810 . In the illustrated example as shown in  FIGS.  48 - 53   , the body portion  4810  may include a first set of mass portions  5020  (e.g., shown as mass portions  5021  and  5022 ), a second set of mass portions  5030  (e.g., shown as mass portions  5031  and  5032 ), a third set of mass portions  5040  (e.g., shown as mass portions  5041 ,  5042 , and  5043 ), and a fourth set of mass portions  5050  (e.g., shown as mass portions  5051  and  5052 ). While the above example may describe a particular number or portions of mass portions, a set of mass portions may include a single mass portion or a plurality of mass portions as described in any of the incorporated by reference applications. For example, any one or a combination of adjacent sets of mass portions of the first set of mass portions  5020  may be a single mass portion, the second set of mass portions  5030  may be a single mass portion, the third set of mass portions  5040  may be a single mass portion, and/or the fourth set of mass portions  5050  may be a single mass portion. Further, the first set of mass portions  5020 , the second set of mass portions  5030 , the third set of mass portions  5040 , and/or the fourth set of mass portions  5050  may be a portion of the physical structure of the body portion  4810 . The mass portions of the first set of mass portions  5020 , the second set of mass portions  5030 , the third set of mass portions  5040 , and/or the fourth set of mass portions  5050  may be similar to any of the mass portions described herein or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  4910  may be partially or entirely filled with one or more filler materials (i.e., a cavity filling material), which may include one or more similar or different types of materials. In one example, as shown in  FIGS.  48 - 53   , the interior cavity  4910  may be filled with a first filler material  5112  and a second filler material  5114 . The first filler material  5112  and the second filler material  5114  may be similar to any of the filler materials described herein or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first filler material  5112  may be coupled to all or portions of the inner walls  4912  of the interior cavity  4910 . In one example, the first filler material  5112  may have inherent adhesive or bonding properties to attach to all or portions of the inner walls  4912 . In another example, the first filler material  5112  may be attached to all or portions of the inner walls  4912  with one or more bonding agents or adhesives that may be mixed with the first filler material  5112 . In another example, the first filler material  5112  may be attached to all or portions of the inner walls  4912  with one or more bonding agents or adhesives that may be separate from the first filler material  5112 . In yet another example, the first filler material  5221  may be attached to all or portions of the inner walls  4912  with the second filler material  5114 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIGS.  48 - 53   , the first filler material  5112  may be coupled to at least a portion of the inner walls  4912  that may generally correspond to the ball strike region  4868  of the face portion  4862  (i.e., the first filler material  5112  may be generally located behind the ball strike region  4868 ) or regions proximate to and/or surrounding the ball strike region  4868  of the face portion  4862 . In another example, the first filler material  5112  may be coupled to at least 10% of the inner walls  4912 . In another example, the first filler material  5112  may be coupled to at least 25% of the inner walls  4912 . In yet another example, the first filler material  5112  may be coupled to between 25% and 50% of the inner walls  4912 . In another example, the first filler material  5112  may be coupled to between 35% and 75% of the inner walls  4912 . In yet another example, the first filler material  5112  may be coupled to between 50% and 90% of the inner walls  4912 . In yet another example, the first filler material  5112  may be coupled to more than 75% of the inner walls  4912 . In yet another example, the first filler material  5112  may be coupled to all inner walls  4912 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The amount of the first filler material  5112  that may be coupled to the inner walls  4912  may depend on the loft angle of the golf club head, the overall thickness of the face portion  4862 , the thickness profile of the face portion  4862 , the shape of the interior cavity  4910 , the locations and configurations of any ports or mass portions, the material properties of the first filler material  5112 , and/or the material properties of the second filler material  5114 . In one example, a golf club head with a relatively high loft angle may limit the portions of the inner walls  4912  to which the first filler material  5112  may be coupled. In another example, a golf club head with a relatively small loft angle may allow the first filler material  5112  to be coupled to all or substantial portions of the inner walls  4912 . In yet another example, the acoustic properties of a golf club head may be a factor in determining the amount of filler material  5112  that may be coupled to the inner walls  4912  to provide a pleasing sound and feel to an individual. The amount (i.e., volume and/or mass) of the first filler material  5112  coupled to the inner walls  4912  may be determined for each golf club head (i.e., having a certain loft angle) to (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  4800  strikes a golf ball as perceived by an individual using the golf club head  4800 ), (ii) provide structural support for the face portion  4862 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  48 - 53   , a central portion  4911  of the interior cavity  4910 , which may be a portion of the interior cavity  4910  that may generally correspond to the ball strike region  4868 , may include the first filler material  5112  and the second filler material  5114 . The width  4913  of the interior cavity  4910  at the central portion  4911  of the interior cavity  4910  may be generally greater than the width  4913  of the interior cavity  4910  at other portions of the interior cavity  4910 . Accordingly, the region of the interior cavity  4910  behind the ball strike region  4868 , i.e., the central portion  4911 , may include a relatively large volume of the first filler material  5112  and/or the second filler material  5114 . Further, the configuration of the central portion  4911  (i.e., size, shape, contour, volume, etc.) may depend on the loft angle  5145 . For example, a golf club head  4800  with a relatively small loft angle  5145  may have a larger central portion  4911  (i.e., larger volume, depth, height, etc.) than a golf club head  4800  with a relatively large loft angle  5145 . Accordingly, as described herein, the amount of first filler material  5112  and/or the second filler material  5114  inside the interior cavity  4910 , and more specifically, in the central portion  4911  may be determined based on the loft angle  5145  to provide (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  4800  strikes a golf ball as perceived by an individual using the golf club head  4800 ), (ii) provide structural support for the face portion  4862 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The contour of the interior cavity  4910  or the shape of the inner walls  4912  may be defined by a plurality of recessed portions that are recessed relative to the perimeter edge portion  4861 . In the example of  FIGS.  48 - 53   , the interior cavity  4910  may include a first recessed portion  4914 , a second recessed portion  4915  that may have a generally smaller depth (i.e., interior cavity width  4913  as viewed in cross section in  FIGS.  51 - 53   ) relative to the first recessed portion  4914 , a third recessed portion  4916  that may have a generally smaller depth than the second recessed portion  4915 , a fourth recessed portion  4917  that may have a generally smaller depth than the third recessed portion  4916 , and a fifth recessed portion  4918  that may have a generally smaller depth than the fourth recessed portion  4917 . The interior cavity  4910  may have more or less recessed portions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first recessed portion  4914  may generally include the largest width  4913  of the interior cavity  4910  and may be located at the central portion  4911  and/or may include portions that are adjacent to or surround the central portion  4911 . The second recessed portion  4915  may be adjacent to all or portions of the first recessed portion  4914  and may include portions that may be in the central portion  4911 . In the example of  FIGS.  48 - 53   , the second recessed portion  4915  is located below the first recessed portion  4914 . A portion of the structure of the body portion  4810  that includes the third set of ports  4940  may be between the second recessed portion  4915  and the lower back wall portion  5214 . Accordingly, the depth of the second recessed portion  4915  may be less than the depth of the first recessed portion  4914  so that the body portion  4810  can accommodate the third set of ports  4940  between the second recessed portion  4915  and the lower back wall portion  5214 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third recessed portion  4916  may be adjacent to and/or surround all or portions of the second recessed portion  4915  and/or the first recessed portion  4914  and may include portions that may be in the central portion  4911 . In the example of  FIGS.  48 - 53   , the third recessed portion  4916  surrounds the first recessed portion  4914  above the horizontal midplane  5120 . The fourth recessed portion  4917  may be at or proximate to the perimeter edge portion  4861 , and/or may be adjacent to and/or surround all or portions of the third recessed portion  4916 , the second recessed portion  4915 , and/or the first recessed portion  4914 . In the example of  FIGS.  48 - 53   , the fourth recessed portion  4917  is adjacent to portions of the first recessed portion  4914  and the second recessed portion  4915  below the horizontal midplane  5120 . A portion of the structure of the body portion  4810  that includes the second set of ports  4930  and the fourth set of ports  4950  may be between the fourth recessed portion  4917  and the lower back wall portion  5214 . Accordingly, the depth of the fourth recessed portion  4917  may be less than the depths of the first recessed portion  4914  and the second recessed portion  4915  so that the body portion  4810  can accommodate the second set of ports  4930  and the fourth set of ports  4950  between the fourth recessed portion  4917  and the lower back wall portion  5214 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The fifth recessed portion  4918  may be adjacent to the perimeter edge portion  4861 . Accordingly, at any location in the interior cavity  4910  that includes the fifth recessed portion  4918 , the fifth recessed portion  4918  may be between the perimeter edge portion  4861  and any one or more of the first recessed portion  4914 , the second recessed portion  4915 , the third recessed portion  4916 , and the fourth recessed portion  4917 . A portion of the structure of the body portion  4810  that includes the first set of ports  4920  may be between the fifth recessed portion  4918  and the upper back wall portion  5212 . Accordingly, the depth of the fifth recessed portion  4918  may be less than the depth of the adjacent portions of the third recessed portion  4916  so that the body portion  4810  can accommodate the first set of ports  4920  between the fifth recessed portion  4918  and the upper back wall portion  5212 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  4910  may include one or more internal channels that may extend between the toe portion  4840  and the heel portion  4850 . In one example, as shown in  FIGS.  48 - 53   , the interior cavity  4910  may include a first internal channel  4925  that may extend from a location at the toe portion  4840  to the central portion  4911 , and a second internal channel  4926  that may extend from a location at the heel portion  4850  to the central portion  4911 . The first internal channel  4925  and the second internal channel  4926  connect to the first recessed portion  4914  and may have the same depth as the first recessed portion  4914  at or proximate to the central portion  4911 . The depths of the first internal channel  4925  and the second internal channel  4926  may diminish from the first recessed portion  4914  toward the toe portion  4840  and heel portion  4850 , respectively. As shown in the example of  FIGS.  48 - 53   , portions of the first internal channel  4925  and/or the second internal channel  4926  that connect to the first recessed portion  4914  and/or are proximate to the first recessed portion  4914  may maintain a constant depth that may be similar to the depth of the first recessed portion  4914 . Accordingly, the first internal channel  4925  and the second internal channel  4926  provide a greater volume of the first filler material  5112  and/or the second filler material  5114  between the central portion  4911  and the toe portion  4840  and the heel portion. Alternatively, all or portions of the first internal channel  4925  and/or the second internal channel  4926  may have diminishing depths in a direction toward the toe portion  4840  and the heel portion  4850 , respectively. For off-center hits of a golf ball with the face portion  4862 , the increased volume of the first filler material  5112  and/or the second filler material  5114  in the internal channels  4925  and  4926  may (i) provide vibration dampening or sound dampening, (ii) provide structural support for the face portion  4862 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. Further, the mass that is removed from the body portion  4810  to provide the internal channels  4925  and  4926  may be shifted to other locations on the body portion  4810  to increase and/or optimize the moment of inertia and the location of the center of gravity of the golf club head  4800 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  4910  may include additional recessed portions that may define transition regions between the first to fifth recessed portions  4914 - 4918  and the internal channels  4925  and  4926 . Each of the recessed portions may be adjacent to and transition into any one or several of the other recessed portions. For example, as shown in  FIGS.  50 - 51   , the first recessed portion  4914  may include an inclined surface  4927  that may transition and connect to the third recessed portion  4916  above the first recessed portion  4914 . Further, any of the recessed portions may directly transition to the perimeter edge portion  4861 . The recessed portions and the transition regions may collectively define the overall shape and/or contour of the interior cavity  4910 . The transition regions may include walls that are perpendicular, transverse, or include relative to adjacent recessed portions. Further, the transition regions may include rounded corners when joining an adjacent recessed portion to reduce stress concentrations at the joined corner. The recessed portions may define a contoured, continuous, and/or stepped reduction of the width of the interior cavity  4910  form the central portion  4911  to the perimeter edge portion  4861 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The shape, size, width, height, and other characteristics of the recessed portions  4914 - 4918  and the internal channels  4925  and  4926  may be associated with the loft angle  5145  of the golf club head  4800 . In one example, as shown in  FIGS.  48 - 53   , the first recessed portion  4914  and the second recessed portion  4915  may be filled with the first filler material  5112 . The first filler material  5112  may be injection molded in the first recessed portion  4914  and the second recessed portion  4915 . The filler material  5112  may be bonded to the inner walls  4912  including the portions of the inner walls  4912  of the first recessed portion  4914  and the second recessed portion  4915  by having inherent adhesive or bonding properties, with a bonding agent that is mixed with the first filler material  5112 , and/or a separate bonding agent. In another example, the first filler material  5112  may be separately molded in the shape of the first recessed portion  4914  and the second recessed portion  4915  and coupled to the first recessed portion  4914  and the second recessed portion  4915  with a bonding agent, and/or with the second filler material  5114 . In one example, the remaining portions of the interior cavity  4910 , which include the third recessed portion  4916 , the fourth recessed portion  4917 , and the fifth recessed portion  4918  may be filled with the second filler material  5114 . Accordingly, the second filler material  5114  may be coupled to the back surface  4866  of the face portion  4862 , coupled to portions of the inner walls  4912  outside the first recessed portion  4914  and the second recessed portion  4915 , coupled to portions of the inner walls  4912  that are not exposed and not coupled to the first filler material  4211 , and/or disposed between the face portion  4862  and the first filler material  5112 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     A width  5122  (W F1 ) of the first filler material  5112  and the width  5124  (W F2 ) of the second filler material  5114  may vary from the toe portion  4840  to the heel portion  4850  and/or from the top portion  4880  to the sole portion  4890  and/or according to the shapes of the first recessed portion  4914 , the second recessed portion  4915 , the third recessed portion  4916 , the fourth recessed portion  4917 , and/or the fifth recessed portion  4918  depending on the location inside the interior cavity  4910 . The width  5122  of the first filler material  5112  may vary according to the shapes of the first recessed portion  4914  and the second recessed portion  4915 . The width  5122  of the first filler material  5112  and/or the width  5124  of the second filler material  5114  may be constant or substantially constant at one or more locations in the interior cavity  4910  and vary at certain other locations in the interior cavity  4910 . In one example, the width  5122  of the first filler material  5112  and/or the width  5124  of the second filler material  5114  may vary at one or more locations in the interior cavity  4910  similar or substantially similar to the contour of all or portions of the inner walls  4912  of the interior cavity  4910  (i.e., the contours of the recessed portions) and/or the contours of the boundaries between the first filler material  5112  and the second filler material  5114 . In one example, the second filler material  5114  may (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  4800  strikes a golf ball as perceived by an individual using the golf club head  4800 ), (ii) provide structural support for the face portion  4862 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The width  5122  of the first filler material  5112  and width  5124  of the second filler material  5114  may be determined at the ball strike region  4868  and/or other regions of the interior cavity  4910  so that a relatively high or optimum coefficient of restitution (COR) is provided for the golf club head  4800 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the first filler material  5112  may be similar to any of the first filler materials described herein such as the first filler material  4211 . In another example, the first filler material  5112  may be a rubber-type of material such as a compound including a mixture of polybutadiene as a base polymer material, and a vulcanizing agent, which may be based on sulfur, peroxides, metallic oxides, acetoxysilane, or urethane crosslinkers. The added vulcanizing agent may facilitate cross linkage between polybutadiene chains to vulcanize or cure the polybutadiene polymer. The amount of vulcanizing agent may be directly related to the resilience of the resulting vulcanized polymer, which may be measured by Yerzley method, ASTM D945-59. In one example, the first filler material  5112  may be formed from a compound including between 3 parts by weight and 7.5 parts by weight of sulfur per 100 parts by weight of polybutadiene. In another example, the first filler material  5112  may be formed from a compound including between 4 parts by weight and 6.25 parts by weight of a vulcanizing agent such as sulfur per 100 parts by weight of polybutadiene. In yet another example, the first filler material  5112  may be formed from a compound including between 4.75 parts by weight and 5.75 parts by weight of sulfur per 100 parts by weight of polybutadiene. The amounts of polybutadiene and sulfur as described herein may yield a compound having a Yerzley resilience of (1) between 75% and 85%, (2) between 80% and 90%, or (3) greater than 90%. The first filler material  5112  and the mixture composition thereof may be similar to any of the compounds described in U.S. Pat. No. 3,241,834, which is incorporated by reference herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Other additives may be combined with the mixture of polybutadiene and the vulcanizing agent to initiate the curing cycle. In particular, an activating agent such as zinc oxide and/or stearic acid may be used to initiate the curing cycle of the mixture of polybutadiene and the vulcanizing agent. In one example, the amount of zinc oxide used may be between 2 parts by weight and 5 parts by weight per 100 parts by weight of polybutadiene, and/or the amount of stearic acid used may be between 0.5 parts by weight and 4 parts by weight per 100 parts by weight of polybutadiene. In another example, the amount of zinc oxide used may be between 2.5 parts by weight and 4.5 parts by weight per 100 parts by weight of polybutadiene, and/or the amount of stearic acid used may be between 1 part by weight and 2 parts by weight per 100 parts by weight of polybutadiene. In yet another example, the amount of zinc oxide used may be between 3.5 parts by weight and 4.5 parts by weight per 100 parts by weight of polybutadiene, and/or the amount of stearic acid used may be between 1.5 parts by weight and 2.5 parts by weight per 100 parts by weight of polybutadiene. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Further, other additives may be combined with the mixture of polybutadiene and the vulcanizing agent to accelerate the rate of vulcanization. Accelerating the rate of vulcanization may shorten the length of the molding cycle of the first filler material  5112  and may also equalize the heat throughout the mixture during the curing cycle. In one example, any one or a combination of N-oxydiethylene benzothiazole 2 sulfenamide (referred to under the trade name AMAX), di-ortho-tolylguanidine (referred to under the trade name DOTG) and bismuth dimethyldithio-carbonate (referred to under the trade name Bismate) may be used to accelerate the vulcanization process. The activation of these accelerators may occur as the mixture reaches a specific temperature. For Bismate and DOTG, the activation temperature is approximately 230° F., whereas the activation temperature of AMAX is approximately 260° F. By ensuring that the heat of reaction is equalized throughout the mixture a more uniform rate of vulcanization and improved consistency in the end product is obtained. In one example, the amount of each of AMAX, DOTG, and Bismate may be between 0.25 and 4 parts by weight per 100 parts by weight of polybutadiene. In another example, the amount of each of AMAX, DOTG, and Bismate may be between 1 and 3 parts by weight per 100 parts by weight of polybutadiene. In yet another example, the amount of each of AMAX, DOTG, and Bismate may be between 1.5 and 2.75 parts by weight per 100 parts by weight of polybutadiene. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Fillers may be added to the mixture of polybutadiene and the vulcanizing agent. In one example, hydrated silica may be added to the mixture as a filler. The added filler material(s) may perform the function of providing tear and abrasion resistance. The filler material may be selected to include to improve the durability of polybutadiene without unduly increasing the specific gravity. In another example, carbon black may be used as a filler material. In yet another example, lithium oxide may be used as a filler material. In one example, the amount of filler material used may be between 4 and 16 parts by weight per 100 parts by weight of polybutadiene. In another example, the amount of filler material used may be between 5 and 10 parts by weight per 100 parts by weight of polybutadiene. In yet another example, the amount of filler material used may be between 7 and 8 parts by weight per 100 parts by weight of polybutadiene. 
     The amount of filler material may affect the specific gravity of the resulting polymer material, which in turn may affect the resilience of the resulting polymer material. In one example, the amount of filler material used in the polybutadiene and the vulcanizing agent mixture may provide a specific gravity of between 1.0 and 1.5 to optimize resilience of the resulting polymer material (i.e. the first filler material  5112 ). In another example, the amount of filler material used in the polybutadiene and the vulcanizing agent mixture may provide a specific gravity of between 1.1 and 1.4 to optimize resilience of the resulting polymer material. In yet another example, the amount of filler material used in the polybutadiene and the vulcanizing agent mixture, the amount of filler material may provide a specific gravity of between 1.0 and 1.05 to optimize resilience of the resulting polymer material. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     One or more anti-oxidation materials may be added to the polymer mixture to prevent oxidation and staining, and/or to inhibit aging of the resulting polymer compound. In one example, 4 methyl-6 tertiary-butyl phenol (referred to under the trade name Antioxidant 2246) may be added to the mixture at an amount of between 0.25 and 3 parts by weight per 100 parts by weight of polybutadiene. Other examples anti-oxidant materials that may be used include phenyl β naphthylamine, alkyl diphenylamine, and/or hindered alkyl phenols. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The various elements of the polymer mixture described herein may be sufficiently mixed to provide uniform distribution of the elements throughout the mixture. In one example, the mixture may then be placed in a mold and subjected to a pressure of between 500 and 3000 pounds per square inch (psi) for a period of approximately 10 to 30 minutes, while concurrently, the temperature of the mixture may be raised to approximately 285-340° F. In another example, the mixture may then be placed in a mold and subjected to a pressure of between 750 and 2000 psi for a period of approximately 12 to 25 minutes, while concurrently, the temperature of the mixture may be raised to approximately 300-330° F. In yet another example, the mixture may then be placed in a mold and subjected to a pressure of between 900 and 1100 psi for a period of approximately 15 to 20 minutes, while concurrently, the temperature of the mixture may be raised to approximately 315-325° F. Various aspects of the treatment of the mixture (e.g., the length of each of the molding operation, the pressure, and/or the temperature) may be adjusted to compensate for any variation in other aspects of the treatment the mixture. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The adhesive for bonding the first filler material  5112  to the portions of the inner walls  4912  may be any type of adhesive that can bond the first filler material  5112  to the material of the face portion  4862 . In one example, the first filler material  5112  may be a rubber or a rubber compound as described herein and the face portion  4862  may be constructed from a steel-based material such as stainless steel. Accordingly, the adhesive for bonding the first filler material  5112  to the portions of the inner walls  4912  may be a type of adhesive used to bond steel-based materials to rubber or rubber compounds. In another example, the first filler material  5112  may be a rubber or a rubber compound and the body portion  3510  may be constructed from titanium or a titanium alloy. Accordingly, the adhesive for bonding the first filler material  5112  to the portions of the inner walls  4912  may be a type of adhesive used to bond titanium-based materials to rubber or rubber compounds. In another example, the second filler material  5114  may be used to bond the first filler material  5112  to the portions of the inner walls  4912 . The bonding of the first filler material  5112  to any portion of the body portion  4810 , the face portion  4862 , and/or the second filler material  5114 , and the bonding of the second filler material  5114  to the body portion  4810 , the face portion  4862 , and/or the first filler material  5112  may be similar to any of the bonding properties and procedures described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example (not shown), the interior cavity  4910  may be entirely filled with the first filler material  5112 . In another example, as shown in  FIGS.  48 - 53   , the interior cavity  4910  may be partially filled with the first filler material  5112 . Accordingly, the remaining portions of the first interior cavity  4910  may be filled with a second filler material  5114 . As described herein, the second filler material  5114  may provide or assist (e.g., alone or in conjunction with one or more adhesives) in the coupling of the first filler material  5112  with portions of the inner walls  4912  and/or with the face portion  4862 . In other words, the second filler material  5114  may assist in maintaining or maintain the first filler material  5112  coupled to the inner walls  4912  and/or the back surface  4866  of the face portion  4862 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The second filler material  5114  may have one or more different properties than the first filler material  5112  such as density, compression, hardness (i.e., durometer), tensile strength, shear strength, viscosity, elasticity, etc., to optimize energy transfer from the face portion  4862  to a golf ball. The second filler material may be a polymer material. The second filler material may be similar to any of the second filler materials described herein such as the second filler material  4213 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The second filler material  5114  may have a smaller COR than the first filler material  5112 . In one example, the COR of the second filler material  5114  may be less than between 1% and 10% of the COR of the first filler material  5112 . In another example, the COR of the second filler material  5114  may be less than between 2% and 5% of the COR of the first filler material  5112 . In another example, the COR of the second filler material  5114  may be between 2% and 4% less than the COR of the first filler material  5112 . 
     In one example, the first filler material  5112  may have a Shore A hardness of between 54 and 76. In another example, the first filler material  5112  may have a Shore A hardness of between 60 and 70. In another example, the first filler material  5112  may have a Shore A hardness of between 62 and 68. In yet another example, the first filler material  5112  may have a Shore A hardness of between 60 and 75. The second filler material  5114  may have a different hardness than the first filler material  5112 . In one example, the second filler material  5114  may have a Shore D hardness of between 55 and 80. In another example, the second filler material  5114  may have a Shore D hardness of between 50 and 85. In another example, the second filler material  5114  may have a Shore D hardness of between 60 and 75. In yet another example, the second filler material  5114  may have a Shore D hardness of between 62 and 73. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the mass of the first filler material  5112  may be between 0.5% and 6.0% of the total mass of the golf club head  4800 . In another example, the mass of the first filler material  5112  may be between 1.0% and 5.0% of the total mass of the golf club head  4800 . In another example, the mass of the first filler material  5112  may be between 2.0% and 4.0% of the total mass of the golf club head  4800 . In another example, the mass of the first filler material  5112  may be greater than 5% of the total mass of the golf club head  4800 . In yet another example, the body portion  4810  may be entirely filled with the first filler material  5112  as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the mass of the second filler material  5114  may be between 2.0% and 14.0% of the total mass of the golf club head  4800 . In another example, the mass of the second filler material  5114  may be between 3.0% and 12.0% of the total mass of the golf club head  4800 . In another example, the mass of the second filler material  5114  may be between 5.0% and 10.0% of the total mass of the golf club head  4800 . In another example, the mass of the second filler material  5114  may greater than 10% of the total mass of the golf club head  4800 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described herein, the face portion  4862  may be relatively thin to provide increased bending and deflection of the face portion  4862  during a golf ball strike. Further, the face portion  4862  may include one or more grooves (e.g., such as the groove  5469  shown in  FIG.  65   ) on the back surface  4866  of the face portion  4862  as described herein to further increase the flexibility of the face portion  4862 . The second filler material  5114  may be a polymer material with a relatively high strength and stiffness to provide structural support and stability for the face portion  4862  to prevent failure of the face portion  4862  during a golf ball strike or repeated golf ball strikes (i.e., face portion fatigue). The second filler material  5114  may also have a relatively high COR as described herein to provide a rebound effect for the face portion  4862  after a golf ball strike. As further described herein, the first filler material  5112  may be a rubber-type of compound with a lower strength and stiffness (i.e., softer or less rigid) than the second filler material  5114  and a higher COR than the second filler material  5114 . Accordingly, the first filler material  5112  may provide additional structural support for the face portion  4862 . Further, the relatively higher COR of the first filler material  5112  may allow the first filler material  5112  to store the energy from a golf ball strike and to release a substantial amount of the energy back to the golf ball (i.e., without losing much impact energy) by providing a relatively large rebound effect for the face portion  4862 . Additionally, the different material properties of the first filler material  5112  and the second filler material  5114  as described herein may provide sound and vibration dampening at different frequency ranges to provide a pleasant sound and feel for an individual. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described herein, the first filler material  5112  may have a resilience (i.e., Yerzley resilience) of (1) between 75% and 85%, (2) between 80% and 90%, or (3) greater than 90%. The relatively high resilience of the first filler material  5112  may be directly related to the rebound velocity and/or acceleration of the face portion  4862  in response to the deflection of the face portion  4862  after the face portion  4862  strikes a golf ball. Accordingly, a golf club head having a first filler material  5112  with a relatively higher resilience may provide a relatively longer distance for a golf ball than a golf club head having a first filler material  5112  with a relatively lower resilience. The amount of compression of the first filler material  5112  may also be directly related to the rebound velocity and/or acceleration of the face portion  4862  after the face portion strikes a golf ball. A certain amount of compression of the first filler material  5112  may provide an optimum rebound effect for the face portion  4862 . Increasing the compression of the first filler material  5112  beyond a certain amount may negatively affect the rebound of the face portion  4862  by dissipating an excessive amount of the compression energy through the first filler material  5112 . Accordingly, the first filler material  5112  may have a relatively high resilience as described herein when the first filler material  5112  is not excessively compressed when the face portion  4862  strikes a golf ball. To control and/or prevent excessive compression of the first filler material  5112 , the second filler material  5114  may be disposed between the face portion  4862  and the first filler material  5112  as described herein. The second filler material  5114  may effectively transfer and uniformly distribute the energy of a golf ball from the face portion  4862  to the first filler material  5112  and prevent excessive compression, and in particular, local compression of the first filler material  5112  to provide an optimum or substantially optimum and generally uniform transfer of the rebound energy from the first filler material  5112  to the face portion  4862 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The second filler material  5114  may also dampen the vibration of the face portion  4862  to provide a certain sound and feel for the golf club head  4800 . Accordingly, the combination of the first filler material  5112  and the second filler material  5114  may dampen the vibration of the face portion  4862  within a broad range of frequencies to provide a certain sound and feel for the golf club head  4800 . The second filler material  5114  may also contribute to providing a certain rebound and/or acceleration for the face portion  4862  to optimize the transfer of energy from the golf club head  4800  to a golf ball. In other words, the second filler material  5114  may cooperatively with the first filler material  5112  optimize the rebounding of the face portion  4862  to maximize the velocity and distance of the golf ball. Further yet, as described herein, the second filler material  5114  may function as an adhesive between the first filler material  5112  and the face portion  4862  to provide continuous and/or uniform energy transfer between the face portion  4862  and the first filler material  5112 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  54 - 65   , a golf club head  5400  may include a body portion  5410  having a toe portion  5440  with a toe portion edge  5442 , a heel portion  5450  with a heel portion edge  5452  that may include a hosel portion  5455  configured to receive a shaft (for example the shaft  9504 ) with a grip (for example the grip  9506 ) on one end and the golf club head  5400  on the opposite end of the shaft to form a golf club, a front portion  5460  with a perimeter edge portion  5461 , a back portion  5470  with a back wall portion  5472 , a top portion  5480  with a top portion edge  5482 , and a sole portion  5490  with a sole portion edge  5492 . The toe portion  5440 , the heel portion  5450 , the front portion  5460 , the back portion  5470 , the top portion  5480 , and/or the sole portion  5490  may partially overlap each other. The toe portion edge  5442 , the heel portion edge  5452 , the top portion edge  5482 , and the sole portion edge  5492  may define a periphery of the body portion  5410 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  5400  may be an iron-type golf club head (e.g., a 1-iron, a 2-iron, a 3-iron, a 4-iron, a 5-iron, a 6-iron, a 7-iron, an 8-iron, a 9-iron, etc.), or a wedge-type golf club head (e.g., a pitching wedge, a lob wedge, a sand wedge, an n-degree wedge such as 44 degrees (°), 48°, 52°, 56°, 60°, etc.). Although  FIGS.  54 - 65    may depict a particular type of club head, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of club heads (e.g., a driver-type club head, a fairway wood-type club head, a hybrid-type club head, a putter-type club head, etc.). The volume of the golf club head  5400 , the materials of construction of the golf club head  5400 , and/or any components thereof may be similar to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  5400  may include a face portion  5462  (i.e., the strike face), which may be integrally formed with the body portion  5410  (e.g., a single unitary piece). In one example, as shown in  FIGS.  54 - 65   , the face portion  5462  may be a separate piece coupled (e.g., adhesively, mechanically, by welding, and/or by soldering) to the front portion  5460 . The face portion  5462  may include a front surface  5464  and a back surface  5466 . In one example (not shown), the front portion  5460  may include one or a plurality of recessed shoulders configured to receive the face portion  5462  for attachment of the face portion  5462  to the body portion  5410 . In another example, as shown in  FIGS.  54 - 65   , the back surface  5466  may include a perimeter portion  5467  that may be attached to a perimeter edge portion  5461  of the body portion  5410 . The perimeter portion  5467  of the face portion  5462  may be attached to the perimeter edge portion  5461  of the body portion  5410  by one or more fasteners, one or more adhesive or bonding agents, and/or welding or soldering. In one example, as shown in  FIGS.  54 - 65   , the perimeter portion  5467  of the face portion  5462  may be welded to the perimeter edge portion  5461  of the body portion  5410  at one or more locations. Alternatively, the entire perimeter portion  5467  of the face portion  5462  may be welded to the entire perimeter edge portion  5461  of the body portion  5410  (i.e., a continuous weld). The face portion  5462  may include a ball strike region  5468  to strike a golf ball. In one example, the center of the ball strike region  5468  may be a geometric center  5463  of the face portion  5462 . In another example, the geometric center  5463  of the face portion  5462  may be offset from a center of the ball strike region  5468 . In one example, the geometric center  5443  and one or more regions near and/or surrounding the geometric center within the ball strike region  5468  may provide a generally optimum location (i.e., optimum ball distance, ball speed, ball spin characteristics, etc.) on the face portion  5462  for striking a golf ball. In yet another example, any location at or near the geometric center  5463  and within the ball strike region  5468  may provide a generally optimum location on the face portion  5462  for striking a golf ball. However, a ball may be struck with any portion of the face portion  5462  within the ball strike region  5468  or outside the ball strike region  5468  for any of the golf club heads described herein resulting in certain ball flight characteristics different from an on-center hit that may be preferred by an individual. The configuration of the face portion  5462  and the attachment of the face portion  5462  (e.g., welding) to the body portion  5410  may be similar in many respects to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  5400  may be associated with a ground plane  5710 , a horizontal midplane  5720 , and a top plane  5730 . In particular, the ground plane  5710  may be a plane that is parallel or substantially parallel to the ground and is tangent to the lowest portion of the sole portion edge  5492  when the golf club head  5400  is at an address position (e.g., the golf club head  5400  aligned to strike a golf ball). A top plane  5730  may be a plane that is tangent to the upper most portion of top portion edge  5482  when the golf club head  5400  is at the address position. The ground and top planes  5710  and  5730 , respectively, may be parallel or substantially parallel to each other. The horizontal midplane  5720  may be vertically halfway between the ground and top planes  5710  and  5730 , respectively. Further, the golf club head  5400  may be associated with a loft plane  5740  defining a loft angle  5745  (α) of the golf club head  5400 . The loft plane  5740  may be a plane that is tangent to the face portion  5462 . The loft angle  5745  may be defined by an angle between the loft plane  5740  and a vertical plane  5750  normal to the ground plane  5710 . 
     The body portion  5410  may be a hollow body including an interior cavity  5510  having inner walls  5512 . The interior cavity  5510  may extend between the front portion  5460 , the back portion  5470 , the top portion  5480 , and the sole portion  5490 . In the example of  FIGS.  54 - 65   , the interior cavity  5510  of the body portion  5410  may be enclosed with and partially defined with the face portion  5462 . The configuration of the interior cavity  5510  (e.g., height, width, volume, shape, etc.), the configuration of the interior cavity  5510  relative to the body portion  5410  (e.g., volume of the interior cavity  5510  relative to the volume of body portion  5410 ), the width and height variation of the interior cavity  5510 , and access to the interior cavity  5510  from one or more ports on the body portion  5410  may be similar to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The back wall portion  5472  of the back portion  5470  may include an upper back wall portion  5812  and a lower back wall portion  5814 . The back wall portion  5472  may include a ledge portion  5816  that may extend between the toe portion edge  5442  and the heel portion edge  5452  in a continuous or discontinuous manner. The lower back wall portion  5814  may be located farther back on the body portion  5410  than the upper back wall portion  5812 , with the ledge portion  5816  defining a transition portion between the upper back wall portion  5812  and the lower back wall portion  5814 . Accordingly, the ledge portion  5816  may extend transverse to the upper back wall portion  5812  and the lower back wall portion  5814 . In one example, as shown in  FIG.  54 - 65   , the ledge portion  5816  may include a first ledge portion  5826  and a second ledge portion  5836 . The first ledge portion  5826  may extend on the back wall portion from the toe portion edge  5442  to a back wall center portion  5840  of the back wall portion  5472 . The second ledge portion  5836  may extend from the center portion  5840  of the back wall portion  5472  to the heel portion edge  5452 . As shown in  FIGS.  54 - 65   , the ledge portion  5816  may provide for a relatively greater mass of the body portion  5410  below the horizontal midplane  5720 , and the mass of the body portion  5410  below the horizontal midplane  5720  to be moved farther back on the body portion  5410 . The width of the ledge portion  5816  may be greater than, equal to, or less than the width of the interior cavity at certain locations of the body portion  5410 . The configuration of the ledge portion  5816  (e.g., width, segments, tapering, shape, etc.) and the properties of the ledge portion  5816  relative to the width of the interior cavity may be similar to any ledge portion or similar structure of any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  5410  may include one or more ports, which may be exterior ports and/or interior ports (e.g., located inside the body portion  5410 ). The inner walls  5512  of the interior cavity  5510  may include one or more ports (not shown). In one example, as shown in  FIGS.  54 - 65   , the back portion  5470  may include one or more ports along or proximate to the periphery of the body portion  5410 . For example, the body portion  5410  may include a first set of ports  5520  (e.g., shown as ports  5521  and  5522 ), a second set of ports  5530  (e.g., shown as ports  5531  and  5532 ), a third set of ports  5540  (e.g., shown as ports  5541 ,  5542 , and  5543 ), and a fourth set of ports  5550  (e.g., shown as ports  5551  and  5552 ). The locations, spacing relative to other ports, and any other configuration of each port of the first set of ports  5520 , the second set of ports  5530 , the third set of ports  5540 , and/or the fourth set of ports  5550  may be similar in many respects to any of the ports described herein or described in any of the incorporated by reference applications. Further, any one or more of the ports of the first set of ports  5520 , the second set of ports  5530 , the third set of ports  5540 , and/or the fourth set of ports  5550  may be connected to interior cavity  5510  through which one or more filler materials may be injected into the interior cavity  5510 . In the example of  FIGS.  54 - 65   , the ports  5521 ,  5531 , and  5551  may be connected to the interior cavity  5510  via openings  5561 ,  5571 , and  5581 , respectively. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Each port of the first set of ports  5520  may be separated by a distance less than the port diameter of any of the ports of the first set of ports  5520 . Each port of the second set of ports  5530  may be separated by a distance less than the port diameter of any of the ports of the second set of ports  5530 . Each port of the third set of ports third set of ports  5540  may be separated by a distance less than the port diameter of any of the ports of the third set of ports  5540 . Each port of the fourth set of ports  5550  may be separated by a distance less than the port diameter of any of the ports of the third set of ports  5550 . In one example, the first set of ports  5520  and the second set of ports  5530  may be spaced apart by a distance greater than the port diameter of any of the ports of the first set of ports  5520  and the second set of ports  5530 . In another example, the second set of ports  5530  and the third set of ports  5540  may be spaced apart by a distance greater than the port diameter of any of the ports of the second set of ports  5530  and the third set of ports  5540 . In yet another example, the third set of ports  5540  and the fourth set of ports  5545  may be spaced apart by a distance greater than the port diameter of any of the ports of the third set of ports  5540  and the fourth set of ports  5550 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Although the figures may depict the ports as separate and individual parts, each set or a combination of adjacent sets of ports of the first, second, third, and fourth sets of ports  5520 ,  5530 ,  5540 , and  5550 , respectively, may be a single port. In one example, all ports of the first set of ports  5520  may be combined into a single port (e.g., a first port). In another example, all ports of the second set of ports  5530  may be combined into a single port (e.g., a second port). In another example, all ports of the third set of ports  5540  may be combined into a single port (e.g., a third port). In yet another example, all ports of the fourth set of ports  5550  may be combined into a single port (e.g., a fourth port). While the figures may depict a particular number of ports, the apparatus, methods, and articles of manufacture described herein may include more or a smaller number of ports. 
     The body portion  5410  may include one or more mass portions (e.g., weight portion(s)), which may be integral mass portion(s) or separate mass portion(s) that may be coupled to the body portion  5410 . In the illustrated example as shown in  FIGS.  54 - 65   , the body portion  5410  may include a first set of mass portions  5620  (e.g., shown as mass portions  5621  and  5622 ), a second set of mass portions  5630  (e.g., shown as mass portions  5631  and  5632 ), a third set of mass portions  5640  (e.g., shown as mass portions  5641 ,  5642 , and  5643 ), and a fourth set of mass portions  5650  (e.g., shown as mass portions  5651  and  5652 ). While the above example may describe a particular number or portions of mass portions, a set of mass portions may include a single mass portion or a plurality of mass portions as described in any of the incorporated by reference applications. For example, any one or a combination of adjacent sets of mass portions of the first set of mass portions  5620  may be a single mass portion, the second set of mass portions  5630  may be a single mass portion, the third set of mass portions  5640  may be a single mass portion, and/or the fourth set of mass portions  5650  may be a single mass portion. Further, the first set of mass portions  5620 , the second set of mass portions  5630 , the third set of mass portions  5640 , and/or the fourth set of mass portions  5650  may be a portion of the physical structure of the body portion  5410 . The mass portions of the first set of mass portions  5620 , the second set of mass portions  5630 , the third set of mass portions  5640 , and/or the fourth set of mass portions  5650  may be similar to any of the mass portions described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  5510  may be partially or entirely filled with one or more filler materials (i.e., a cavity filling material), which may include one or more similar or different types of materials. In one example, as shown in  FIGS.  54 - 65   , the interior cavity  5510  may be filled with a first filler material  5712  and a second filler material  5714 . In one example, the first filler material  5712  may be similar to the first filler material  5112 , and the second filler material  5714  may be similar to the second filler material  5114  as described herein. Accordingly, the first filler material  5712  may be a rubber or rubber compound, and the second filler material  5714  may be an epoxy-type of material. In another example, the first filler material  5712  and/or the second filler material  5714  may be similar to any of the filler materials described herein or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first filler material  5712  may be coupled to all or portions of the inner walls  5512  of the interior cavity  5510 . In one example, the first filler material  5712  may have inherent adhesive or bonding properties to attach to all or portions of the inner walls  5512 . In another example, the first filler material  5712  may be attached to all or portions of the inner walls  5512  with one or more bonding agents or adhesives that may be mixed with the first filler material  5712 . In another example, the first filler material  5712  may be attached to all or portions of the inner walls  5512  with one or more bonding agents or adhesives that may be separate from the first filler material  5712 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIGS.  56  and  57   , the first filler material  5712  may be coupled to at least a portion of the inner walls  5512  that may generally correspond to the ball strike region  5468  of the face portion  5462  (i.e., the first filler material  5712  may be generally located behind the ball strike region  5468 ) or regions proximate to and/or surrounding the ball strike region  5468  of the face portion  5462 . In another example, the first filler material  5712  may be coupled to at least 10% of the inner walls  5512 . In another example, the first filler material  5712  may be coupled to at least 25% of the inner walls  5512 . In yet another example, the first filler material  5712  may be coupled to between 25% and 50% of the inner walls  5512 . In another example, the first filler material  5712  may be coupled to between 41% and 75% of the inner walls  5512 . In yet another example, the first filler material  5712  may be coupled to between 50% and 90% of the inner walls  5512 . In yet another example, the first filler material  5712  may be coupled to more than 75% of the inner walls  5512 . In yet another example, the first filler material  5712  may be coupled to all of inner walls  5512 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in Table 4, a range of volumes of the first filler material  5712  (V r ) may be expressed relative to the volume of the body portion  5410  (V b ) and relative to the volume of the interior cavity  5510  (V c ). Further, as shown in Table 4, the mass of the first filler material  5712  (m r ) and the mass of the second filler material  5714  (m f ) may be expressed relative to the mass of the body portion  5410  (m b ). 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Golf Club Head 5400 
                 V r /V b   
                 V r /Vc 
                 m r /m b   
                 m f /m b   
               
               
                   
               
             
            
               
                 3-iron 
                 9% to 17% 
                 22% to 40% 
                 1.7% to 3.1% 
                 4.3% to 8.0% 
               
               
                 4-iron 
                 10% to 18%  
                 24% to 44% 
                 1.8% to 3.3% 
                 4.1% to 7.5% 
               
               
                 5-iron 
                 9% to 17% 
                 24% to 44% 
                 1.7% to 3.1% 
                 3.8% to 7.1% 
               
               
                 6-iron 
                 8% to 16% 
                 23% to 42% 
                 1.5% to 2.8% 
                 3.7% to 6.9% 
               
               
                 7-iron 
                 8% to 15% 
                 23% to 43% 
                 1.5% to 2.7% 
                 3.5% to 6.5% 
               
               
                 8-iron 
                 8% to 16% 
                 23% to 42% 
                 1.5% to 2.8% 
                 3.7% to 6.8% 
               
               
                 9-iron 
                 8% to 15% 
                 23% to 42% 
                 1.4% to 2.6% 
                 3.4% to 6.4% 
               
               
                 Pitching Wedge 
                 8% to 14% 
                 22% to 41% 
                 1.3% to 2.5% 
                 3.4% to 6.3% 
               
               
                 Gap Wedge 
                 7% to 13% 
                 21% to 40% 
                 1.2% to 2.2% 
                 3.1% to 5.7% 
               
               
                   
               
            
           
         
       
     
     As shown in the example of Table 4, the amount of the first filler material  5712  that may be in the interior cavity  5510  and/or coupled to the inner walls  5512  may depend on the loft angle of the golf club head (e.g., 4-iron, 7-iron, PW, etc.). In another example, the ratio of the volume of the first filler material  5712  to the volume of the body portion  5410  may be greater than or equal to 2.5% and less than or equal to 30%. In another example, the ratio of the volume of the first filler material  5712  to the volume of the interior cavity  5510  may be greater than or equal to 15% and less than or equal to 50%. In another example, the ratio of the mass of the first filler material  5712  to the mass of the body portion  5410  may be greater than or equal to 0.75% and less than or equal to 7.5%. In another example, the ratio of the volume of the first filler material  5712  to the volume of the interior cavity  5510  may be greater than 50%. In another example, the ratio of the volume of the first filler material  5712  to the volume of interior cavity  5510  may be 100% or near 100% (i.e., the interior cavity  5510  is entirely filled with the first filler material  5712 ). In yet another example, a ratio of the mass of second filler material  5712  to the mass of the body portion  5410  may be greater than or equal to 2.0% and less than or equal to 10%. Although Table 4 lists golf club heads that are labeled as having a certain loft angles or loft angle ranges, each of the golf club heads of Table 4 may include a certain loft angle range that may be partially similar or overlap with the loft angle range of an adjacent golf club head of Table 4. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The amount of first filler material  5712  that may be in the interior cavity may also depend on the overall thickness of the face portion  5462 , the thickness profile of the face portion  5462 , the shape of the interior cavity  5510 , the locations and configurations of any ports or mass portions, the material properties of the first filler material  5712 , and/or the material properties of the second filler material  5714 . In one example, a golf club head with a relatively high loft angle may limit the portions of the inner walls  5512  to which the first filler material  5712  may be coupled. In another example, a golf club head with a relatively small loft angle may allow the first filler material  5712  to be coupled to all or substantial portions of the inner walls  5512 . In yet another example, the acoustic properties of a golf club head may be a factor in determining the amount of filler material  5712  that may be coupled to the inner walls  5512  to provide a pleasing sound and feel to an individual. The amount (i.e., volume and/or mass) of the first filler material  5712  coupled to the inner walls  5512  may be determined for each golf club head (i.e., having a certain loft angle) to (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  5400  strikes a golf ball as perceived by an individual using the golf club head  5400 ), (ii) provide structural support for the face portion  5462 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  54 - 65   , a portion of the interior cavity  5510  including a central portion  5511  of the interior cavity  5510 , which may be a portion of the interior cavity  5510  that may generally correspond to the ball strike region  5468 , may be include the first filler material  5712  and the second filler material  5714 . The width  5513  of the interior cavity  5510  at the central portion  5511  of the interior cavity  5510  may be generally greater than the width  5513  of the interior cavity  5510  at other portions of the interior cavity  5510 . Accordingly, the region of the interior cavity  5510  behind the ball strike region  5468 , i.e., the central portion  5511 , may include a relatively large volume of the first filler material  5712  and/or the second filler material  5714 . Further, the configuration of the central portion  5511  (i.e., size, shape, contour, volume, etc.) may depend on the loft angle  5745 . For example, a golf club head  5400  with a relatively small loft angle  5745  may have a larger central portion  5511  (i.e., larger volume, depth, height, etc.) than a golf club head  5400  with a relatively large loft angle  5745 . Accordingly, as described herein, the amount of first filler material  5712  and/or the second filler material  5714  inside the interior cavity  5510 , and more specifically, in the central portion  5511  may be determined based on the loft angle  5745  to provide (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  5400  strikes a golf ball as perceived by an individual using the golf club head  5400 ), (ii) provide structural support for the face portion  5462 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The contour of the interior cavity  5510  or the shape of the inner walls  5512  may be defined by a plurality of recessed portions that may be recessed relative to the perimeter edge portion  5461 . In the example of  FIGS.  54 - 65   , the interior cavity  5510  may include a first recessed portion  5514 , a second recessed portion  5515  that may have a generally smaller depth (i.e., defined by the interior cavity width  5513  as viewed in cross section in  FIGS.  57 - 40   ) relative to the first recessed portion  5514 , a third recessed portion  5516  that may have a generally smaller depth than the second recessed portion  5515 , a fourth recessed portion  5517  that may have a generally smaller depth than the third recessed portion  5516 , and a fifth recessed portion  5518  that may have a generally smaller depth than the fourth recessed portion  5517 . The interior cavity  5510  may have more or less recessed portions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first recessed portion  5514  may generally include a largest width  5513  of the interior cavity  5510  and may be located at the central portion  5511  and/or may include portions that are adjacent to and/or surround the central portion  5511 . The second recessed portion  5515  may be adjacent to and/or surround all or portions of the first recessed portion  5514 , and may include portions that may be in the central portion  5511 . In the example of  FIGS.  54 - 65   , the second recessed portion  5515  is located below the first recessed portion  5514 . A portion of the structure of the body portion  5410  that includes the third set of ports  5540  may be between the second recessed portion  5515  and the lower back wall portion  5814 . Accordingly, the depth of the second recessed portion  5515  may be less than the depth of the first recessed portion  5514  so that the body portion  5410  can accommodate the third set of ports  5540  between the second recessed portion  5515  and the lower back wall portion  5814 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third recessed portion  5516  may be adjacent to and/or surround all or portions of the second recessed portion  5515  and/or the first recessed portion  5514 , and may include portions that may be in the central portion  5511 . In the example of  FIGS.  54 - 65   , the third recessed portion  5516  surrounds the first recessed portion  5514  above the horizontal midplane  5720 . The fourth recessed portion  5517  may be at or proximate to the perimeter edge portion  5461 , and/or may be adjacent to and/or surround all or portions of the third recessed portion  5516 , the second recessed portion  5515 , and/or the first recessed portion  5514 . In the example of  FIGS.  54 - 65   , the fourth recessed portion  5517  is adjacent to portions of the first recessed portion  5514  and the second recessed portion  5515  below the horizontal midplane  5720 . A portion of the structure of the body portion  5410  that includes the second set of ports  5530  and the fourth set of ports  5550  may be between the fourth recessed portion  5517  and the lower back wall portion  5814 . Accordingly, the depth of the fourth recessed portion  5517  may be less than the depths of the first recessed portion  5514  and the second recessed portion  5515  so that the body portion  5410  can accommodate the second set of ports  5530  and the fourth set of ports  5550  between the fourth recessed portion  5517  and the lower back wall portion  5814 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The fifth recessed portion  5518  may be adjacent to the perimeter edge portion  5461 . Accordingly, at any location in the interior cavity  5510  that includes the fifth recessed portion  5518 , the fifth recessed portion  5518  may be between the perimeter edge portion  5461  and any one or more of the first recessed portion  5514 , the second recessed portion  5515 , the third recessed portion  5516 , and the fourth recessed portion  5517 . A portion of the structure of the body portion  5410  that includes the first set of ports  5520  may be between the fifth recessed portion  5518  and the upper back wall portion  5812 . Accordingly, the depth of the fifth recessed portion  5518  may be less than the depth of the adjacent portions of the third recessed portion  5516  so that the body portion  5410  can accommodate the first set of ports  5520  between the fifth recessed portion  5518  and the upper back wall portion  5812 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  5510  may include one or more internal channels that may extend between the toe portion  5440  and the heel portion  5450 . In one example, as shown in  FIGS.  54 - 65   , the interior cavity  5510  may include a first internal channel  5525  that may extend from a location at the toe portion  5440  to the central portion  5511 , and a second internal channel  5526  that may extend from a location at the heel portion  5450  to the central portion  5511 . The first internal channel  5525  and the second internal channel  5526  connect to the first recessed portion  5514  and may have the same depth as the first recessed portion  5514  at or proximate to the central portion  5511 . The depths of the first internal channel  5525  and the second internal channel  5526  may diminish from the first recessed portion  5514  toward the toe portion  5440  and heel portion  5450 , respectively. As shown in the example of  FIGS.  54 - 65   , portions of the first internal channel  5525  and/or the second internal channel  5526  that connect to the first recessed portion  5514  and/or are proximate to the first recessed portion  5514  may maintain a constant depth that may be similar to the depth of the first recessed portion  5514 . Alternatively, all or portions of the first internal channel  5525  and/or the second internal channel  5526  may have diminishing depths in a direction toward the toe portion  5440  and the heel portion  5450 , respectively. In one example, as shown in  FIGS.  54 - 65   , the height of first internal channel  5525  increases in a direction from the toe portion  5440  to the central portion  5511  to include a relatively large and expanding triangular first channel portion  5535 . Similarly, the height of the second internal channel  5526  increases in a direction from the heel portion  5450  to the central portion  5511  to include a relatively large and expanding triangular second channel portion  5536 . The first channel portion  5535  and the second channel portion  5536  may effectively expand the central portion  5511  further toward the toe portion  5440  and the heel portion  5450 , respectively. Accordingly, the first internal channel  5525  and the second internal channel  5526  may provide a greater volume of the first filler material  5712  and/or the second filler material  5714  between the central portion  5511  and the toe portion  5440  and the heel portion. For off-center hits of a golf ball with the face portion  5462 , the increased volume of the first filler material  5712  and/or the second filler material  5714  in the internal channels  5525  and  5526  may (i) provide vibration dampening or sound dampening, (ii) provide structural support for the face portion  5462 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. Further, the mass that is removed from the body portion  5410  to provide the internal channels  5525  and  5526 , and more specifically, the first channel portion  5535  and the second channel portion  5536 , may be shifted to other locations on the body portion  5410  to increase and/or optimize the moment of inertia and the location of the center of gravity of the golf club head  5400 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  5510  may include additional recessed portions that may define transition regions between the first to fifth recessed portions  5514 - 5518  and the internal channels  5525  and  5526 . Each of the recessed portions may be adjacent to and transition into any one or several of the other recessed portions. For example, as shown in  FIGS.  57 - 59   , the first recessed portion  5514  may include an inclined surface  5527  that may transition and connect to the third recessed portion  5516  above the first recessed portion  5514 . Further, any of the recessed portions may directly transition to the perimeter edge portion  5461 . The recessed portions and the transition regions may collectively define the overall shape and/or contour of the interior cavity  5510 . The transition regions may include walls that are perpendicular, transverse, or include relative to adjacent recessed portions. Further, the transition regions may include rounded corners when joining an adjacent recessed portion to reduce stress concentrations at the joined corner. The recessed portions may define a contoured, continuous, and/or stepped reduction of the width of the interior cavity  5510  form the central portion  5511  to the perimeter edge portion  5461 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The shape, size, width, height, and other characteristics of the recessed portions  5514 - 5518  and the internal channels  5525  and  5526  may be associated with the loft angle  5745  of the golf club head  5400 . In one example, as shown in  FIGS.  54 - 65   , the first recessed portion  5514 , the second recessed portion  5515 , the third recessed portion  5516 , and the internal channels  5525  and  5526  may be filled with the first filler material  5712 . The first filler material  5712  may be injection molded in the first recessed portion  5514 , the second recessed portion  5515 , the third recessed portion  5516 , and the internal channels  5525  and  5526 . The filler material  5712  may be bonded to the inner walls  5512  of the first recessed portion  5514 , the second recessed portion  5515 , the third recessed portion  5516 , and the internal channels  5525  and  5526  by having inherent adhesive or bonding properties, with a bonding agent that is mixed with the first filler material  5712 , and/or a separate bonding agent. In another example, the first filler material  5712  may be separately molded in the shape of the first recessed portion  5514 , the second recessed portion  5515 , the third recessed portion  5516 , and the internal channels  5525  and  5526 , and coupled to the first recessed portion  5514 , the second recessed portion  5515 , the third recessed portion  5516 , and the internal channels  5525  and  5526  with a bonding agent. In one example, the remaining portions of the interior cavity  5510 , which include the fourth recessed portion  5517  and the fifth recessed portion  5518  may be filled with the second filler material  5714 . Accordingly, the second filler material  5714  may be coupled to the back surface  5466  of the face portion  5462 , coupled to portions of the inner walls  5512  outside the first recessed portion  5514 , the second recessed portion  5515 , and the third recessed portion  5516 , and/or disposed between the face portion  5462  and the first filler material  5712 . In another example, the first recessed portion  5514  and the second recessed portion  5515  may be filled with the first filler material  5712 , whereas the remaining portions of the interior cavity  5510  may be filled with the second filler material  5714 . In another example, the first recessed portion  5514 , the second recessed portion  5515 , and the internal channels  5525  and  5526  may be filled with the first filler material  5712 , whereas the remaining portions of the interior cavity  5510  may be filled with the second filler material  5714 . In another example, the first recessed portion  5514 , the second recessed portion  5515 , the internal channels  5525  and  5526 , the third recessed portion  5516  and the fifth recessed portions  5518  may be filled with the first filler material  5712 , whereas the remaining portions of the interior cavity  5510  may be filled with the second filler material  5714 . In yet another example, the entire interior cavity  5510  may be filled with the first filler material  5712 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     A width  5722  (W F1 ) of the first filler material  5712  and the width  5724  (W F2 ) of the second filler material  5714  may vary from the toe portion  5440  to the heel portion  5450  and/or from the top portion  5480  to the sole portion  5490  and/or according to the shapes of the first recessed portion  5514 , the second recessed portion  5515 , the third recessed portion  5516 , the fourth recessed portion  5517 , and/or the fifth recessed portion  5518  depending on the location inside the interior cavity  5510 . The width  5722  of the first filler material  5712  may vary according to the shapes of the first recessed portion  5514 , the second recessed portion  5515 , and the third recessed portion  5516 . The width  5722  of the first filler material  5712  and/or the width  5724  of the second filler material  5714  may be constant or substantially constant at one or more locations in the interior cavity  5510  and vary at certain other locations in the interior cavity  5510 . In one example, the width  5722  of the first filler material  5712  and/or the width  5724  of the second filler material  5714  may vary at one or more locations in the interior cavity  5510  similar or substantially similar to the contour of all or portions of the inner walls  5512  of the interior cavity  5510  (i.e., the contours of the recessed portions) and/or the contours of the boundaries between the first filler material  5712  and the second filler material  5714 . In one example, the second filler material  5714  may (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  5400  strikes a golf ball as perceived by an individual using the golf club head  5400 ), (ii) provide structural support for the face portion  5462 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The width  5722  of the first filler material  5712  and width  5724  of the second filler material  5714  may be determined at the ball strike region  5468  and/or other regions of the interior cavity  5510  so that a relatively high or optimum coefficient of restitution (COR) is provided for the golf club head  5400 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example (not shown), the interior cavity  5510  may be entirely filled with the first filler material  5712 . In another example, as shown in  FIGS.  54 - 65   , the interior cavity  5510  may be partially filled with the first filler material  5712 . Accordingly, the remaining portions of the first interior cavity  5510  may be filled with a second filler material  5714 . As described herein, the second filler material  5714  may provide or assist (e.g., alone or in conjunction with one or more adhesives) in the coupling of the first filler material  5712  with the back wall portion  5472 . In other words, the second filler material  5714  may assist in maintaining or maintain the first filler material  5712  coupled to the back wall portion  5472 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  65   , the back surface  5466  of the face portion  5462  may include one or more grooves proximate to the perimeter portion  5467  of the face portion  5462 . In one example, as shown in  FIG.  65   , a groove  5469  may be a continuous groove (i.e., defining a loop) extending in a path similar to the path of the perimeter portion  5467  proximate to the perimeter portion  5467 . The groove  5469  may include a relatively thinner portion of the face portion  5462 . Accordingly, the groove  5469  may increase the flexibility of the face portion  5462  so that when a golf ball strikes the face portion  5462 , the face portion  5462  provides a greater rebound (i.e., a greater trampoline effect), and hence may provide a greater velocity for the golf ball. All or portions of the groove  5469  may be filled with the first filler material  5712  and/or second filler material  5714 . In the example of the golf club head  5400 , all of the groove  5469  may be filled with the second filler material  5714 . Accordingly, the second filler material  5714  may structurally support the relatively thinner portions of the face portion  5462  defined by the groove  5469 . In another example, a plurality of separate grooves (not shown) may be provided on the back surface  5466  of the face portion  5462  at certain locations proximate to the perimeter portion  5467  to provide a certain rebound effect for the face portion  5462 . In yet another example, a continuous groove similar to the groove  5469  and/or a plurality of separate grooves (not shown) may be provided at certain locations between the perimeter portion  5467  and the geometric center  5463  on the back surface  5466  of the face portion  5462  to provide a certain rebound effect for the face portion  5462 . The face portion of any of the golf club heads described herein may include the groove  5469 . For example, the face portion  3562  of the golf club head  3500  of  FIG.  35    may include a similar groove that may be filled with the second filler material  3814  and/or the first filler material  3812 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described herein, the face portion  5462  may be relatively thin to provide increased bending and deflection of the face portion  5462  during a golf ball strike. Further, the face portion  4862  may include one or more grooves such as the groove  5469  on the back surface  5466  of the face portion  5462  as described herein to further increase the flexibility of the face portion  5462 . The second filler material  5714  may be a polymer material with a relatively high strength and stiffness to provide structural support and stability for the face portion  5462  to prevent failure of the face portion  5462  during a golf ball strike or repeated golf ball strikes (i.e., face portion fatigue). As described herein, the second filler material  5714  may be an epoxy-type of material. The second filler material  5714  may also have a relatively high COR as described herein to provide a rebound effect for the face portion  5462  after a golf ball strike. As further described herein, the first filler material  5712  may be a rubber-type of compound with a lower strength and stiffness (i.e., softer or less rigid) than the second filler material  5714  and a higher COR than the second filler material  5714 . Accordingly, the first filler material  5712  may provide additional structural support for the face portion  5462 . Further, the relatively higher COR of the first filler material  5712  may allow the first filler material  5712  to store the energy from a golf ball strike and to release a substantial amount of the energy back to the golf ball (i.e., without losing much impact energy) by providing a relatively large rebound effect for the face portion  5462 . Additionally, the different material properties of the first filler material  5712  and the second filler material  5714  as described herein may provide sound and vibration dampening at different frequency ranges to provide a pleasant sound and feel for an individual. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
       FIG.  66    depicts one manner by which the golf club head  5400  or any of the golf club heads described herein may be manufactured. In the example of  FIG.  66   , the process  6600  may begin with providing a body portion  5410  and a face portion  5462  of a golf club head  5400  (block  6610 ). The first filler material  5712  may be coupled to the interior cavity  5510  (block  6620 ). In one example, the first filler material  5712  may be formed in one or more recessed portions as described herein (i.e., any of the recessed portions described herein) of the interior cavity  5510  by injection molding. The first filler material  5712  may then cure at ambient temperature or by one or more heating/cooling cycles depending on the material used for the first filler material  5712 . In another example, the first filler material  5712  may be molded into the shape of one or more recessed portions as described herein and then coupled to the one or more recessed portions with a bonding agent as described herein. The face portion  5462  may then be attached to the body portion  5410  as described herein to enclose the interior cavity  5510  (block  6630 ). The second filler material  5714  may then be injected into the interior cavity  5510  through one or more of the ports of the first set of ports  5520 , the second set of ports  5530 , the third set of ports  5540 , and/or the fourth set of ports  5550  that may be connected to the interior cavity  5510  as described herein (block  6640 ). The second filler material  5714  may then cure at ambient temperature or by one or more heating/cooling cycles depending on the material used for the second filler material  5714 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  67 - 86   , a golf club head  6700  may include a body portion  6710  having a toe portion  6740  with a toe portion edge  6742 , a heel portion  6750  with a heel portion edge  6752  that may include a hosel portion  6755  configured to receive a shaft (for example the shaft  9504 ) with a grip (for example the grip  9506 ) on one end and the golf club head  6700  on the opposite end of the shaft to form a golf club, a front portion  6760  with a perimeter edge portion  6761 , a back portion  6770  with a back wall portion  6772 , a top portion  6780  with a top portion edge  6782 , and a sole portion  6790  with a sole portion edge  6792 . The toe portion  6740 , the heel portion  6750 , the front portion  6760 , the back portion  6770 , the top portion  6780 , and/or the sole portion  6790  may partially overlap each other. The toe portion edge  6742 , the heel portion edge  6752 , the top portion edge  6782 , and the sole portion edge  6792  may define a periphery of the body portion  6710 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  6700  may be an iron-type golf club head (e.g., a 1-iron, a 2-iron, a 3-iron, a 4-iron, a 5-iron, a 6-iron, a 7-iron, an 8-iron, a 9-iron, etc.), or a wedge-type golf club head (e.g., a pitching wedge, a lob wedge, a sand wedge, an n-degree wedge such as 44 degrees (°), 48°, 52°, 56°, 60°, etc.). Although  FIGS.  67 - 86    may depict a particular type of club head, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of club heads (e.g., a driver-type club head, a fairway wood-type club head, a hybrid-type club head, a putter-type club head, etc.). The volume of the golf club head  6700 , the materials of construction of the golf club head  6700 , and/or any components thereof may be similar to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  6700  may include a face portion  6762  (i.e., the strike face), which may be integrally formed with the body portion  6710  (e.g., a single unitary piece). In one example, as shown in  FIGS.  67 - 86   , the face portion  6762  may be a separate piece coupled (e.g., adhesively, mechanically, by welding, and/or by soldering) to the front portion  6760 . The face portion  6762  may include a front surface  6764  and a back surface  6766 . In one example (not shown), the front portion  6760  may include one or a plurality of recessed shoulders configured to receive the face portion  6762  for attachment of the face portion  6762  to the body portion  6710 . In another example, as shown in  FIGS.  67 - 86   , the back surface  6766  may include a perimeter portion  6767  that may be attached to a perimeter edge portion  6761  of the body portion  6710 . The perimeter portion  6767  of the face portion  6762  may be attached to the perimeter edge portion  6761  of the body portion  6710  by one or more fasteners, one or more adhesive or bonding agents, and/or welding or soldering. In one example, as shown in  FIGS.  67 - 86   , the perimeter portion  6767  of the face portion  6762  may be welded to the perimeter edge portion  6761  of the body portion  6710  at one or more locations. Alternatively, the entire perimeter portion  6767  of the face portion  6762  may be welded to the entire perimeter edge portion  6761  of the body portion  6710  (i.e., a continuous weld). The face portion  6762  may include a ball strike region  6768  to strike a golf ball. In one example, the center of the ball strike region  6768  may be a geometric center  6763  of the face portion  6762 . In another example, the geometric center  6763  of the face portion  6762  may be offset from a center of the ball strike region  6768 . In one example, the geometric center  6743  and one or more regions near and/or surrounding the geometric center within the ball strike region  6768  may provide a generally optimum location (i.e., optimum ball distance, ball speed, ball spin characteristics, etc.) on the face portion  6762  for striking a golf ball. In yet another example, any location at or near the geometric center  6763  and within the ball strike region  6768  may provide a generally optimum location on the face portion  6762  for striking a golf ball. However, a ball may be struck with any portion of the face portion  4862  within the ball strike region  6768  or outside the ball strike region  6768  for any of the golf club heads described herein resulting in certain ball flight characteristics different from an on-center hit that may be preferred by an individual. The configuration of the face portion  6762  and the attachment of the face portion  6762  (e.g., welding) to the body portion  6710  may be similar in many respects to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The face portion  6762  may include a groove  6769  (shown in  FIG.  72   ) that may be similar in many respects to the groove  5469  of the golf club head  5400 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  6700  may be associated with a ground plane  7010 , a horizontal midplane  7020 , and a top plane  7030 . In particular, the ground plane  7010  may be a plane that is parallel or substantially parallel to the ground and is tangent to the lowest portion of the sole portion edge  6792  when the golf club head  6700  is at an address position (e.g., the golf club head  6700  aligned to strike a golf ball). A top plane  7030  may be a plane that is tangent to the upper most portion of top portion edge  6782  when the golf club head  6700  is at the address position. The ground and top planes  7010  and  7030 , respectively, may be parallel or substantially parallel to each other. The horizontal midplane  7020  may be vertically halfway between the ground and top planes  7010  and  7030 , respectively. Further, the golf club head  6700  may be associated with a loft plane  7040  defining a loft angle  7045  (α) of the golf club head  6700 . The loft plane  7040  may be a plane that is tangent to the face portion  6762 . The loft angle  7045  may be defined by an angle between the loft plane  7040  and a vertical plane  7050  normal to the ground plane  7010 . 
     The body portion  6710  may be a hollow body including an interior cavity  6810  having inner walls  6812 . The interior cavity  6810  may extend between the front portion  6760 , the back portion  6770 , the top portion  6780 , and the sole portion  6790 . In the example of  FIGS.  67 - 86   , the interior cavity  6810  of the body portion  6710  may be enclosed with and partially defined with the face portion  6762 . The configuration of the interior cavity  6810  (e.g., height, width, volume, shape, etc.), the configuration of the interior cavity  6810  relative to the body portion  6710  (e.g., volume of the interior cavity  6810  relative to the volume of body portion  6710 ), the width and height variation of the interior cavity  6810 , and access to the interior cavity  6810  from one or more ports on the body portion  6710  may be similar to any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The back wall portion  6772  of the back portion  6770  may include an upper back wall portion  7112  and a lower back wall portion  7114 . The back wall portion  6772  may include a ledge portion  7116  that may extend between the toe portion edge  6742  and the heel portion edge  6752  in a continuous or discontinuous manner. The lower back wall portion  7114  may be located farther back on the body portion  6710  than the upper back wall portion  7112 , with the ledge portion  7116  defining a transition portion between the upper back wall portion  7112  and the lower back wall portion  7114 . Accordingly, the ledge portion  7116  may extend transverse to the upper back wall portion  7112  and the lower back wall portion  7114 . In one example, as shown in  FIG.  67 - 86   , the ledge portion  7116  may include a first ledge portion  7126  and a second ledge portion  7136 . The first ledge portion  7126  may extend on the back wall portion from the toe portion edge  6742  to a back wall center portion  7140  of the back wall portion  6772 . The second ledge portion  7136  may extend from the center portion  7140  of the back wall portion  6772  to the heel portion edge  6752 . As shown in  FIGS.  67 - 86   , the ledge portion  7116  may provide for a relatively greater mass of the body portion  6710  below the horizontal midplane  7020 , and the mass of the body portion  6710  below the horizontal midplane  7020  to be moved farther back on the body portion  6710 . The width of the ledge portion  7116  may be greater than, equal to, or less than the width of the interior cavity at certain locations of the body portion  6710 . The configuration of the ledge portion  7116  (e.g., width, segments, tapering, shape, etc.) and the properties of the ledge portion  7116  relative to the width of the interior cavity may be similar to any ledge portion or similar structure of any of the golf club heads described herein and/or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  6710  may include one or more ports, which may be exterior ports and/or interior ports (e.g., located inside the body portion  6710 ). The inner walls  6812  of the interior cavity  6810  may include one or more ports (not shown). In one example, as shown in  FIGS.  67 - 86   , the back portion  6770  may include one or more ports along or proximate to the periphery of the body portion  6710 . For example, the body portion  6710  may include a set of ports  6820  (e.g., shown as port  6821 ,  6822 ,  6823 ,  6824 , and  6825 . Each port of the set of ports  6820  may be separated by a distance less than, equal to, or greater than the port diameter of any of the ports of the set of ports  6820 . In one example, the ports  6821  and  6822  may be separated by a distance greater than the port diameter of any of the ports  6821  or  6822 . Similarly, the ports  6824  and  6825  may be separated by a distance greater than the port diameter of any of the ports  6824  or  6825 . The ports  6822 ,  6823 , and  6824  may be separated by a distance less than the port diameter of any of the ports  6822 ,  6823 , or  6824 . Any one or more of the ports of the set of ports  6820  may be combined into a single port. The locations, spacing relative to other ports, and any other configuration of each port of the set of ports  6820  may be similar in many respects to any of the ports described herein or described in any of the incorporated by reference applications. Further, any one or more of the ports of the set of ports  6820  may be connected to interior cavity  6810  through which one or more filler materials may be injected into the interior cavity  6810 . In the example of  FIGS.  67 - 86   , the ports  6821  and  6825  may be connected to the interior cavity  6810  via openings  6861  and  6871 , respectively. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  6710  may include one or more mass portions (e.g., weight portion(s)), which may be integral mass portion(s) or separate mass portion(s) that may be coupled to the body portion  6710 . In the illustrated example as shown in  FIGS.  67 - 86   , the body portion  6710  may include a set of mass portions  6920  (e.g., shown as mass portions  6921 ,  6922 ,  6923 ,  6924 , and  6925 ). While the above example may describe a particular number or portions of mass portions, a set of mass portions may include a single mass portion or a plurality of mass portions as described in any of the incorporated by reference applications. For example, any one or a combination of adjacent mass portions of the set of mass portions  6920  may be a single mass portion. Further, the set of mass portions  6920  may be a portion of the physical structure of the body portion  6710 . The mass portions of the set of mass portions  6920  may be similar to any of the mass portions described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  6810  may be partially or entirely filled with one or more filler materials (i.e., a cavity filling material) as described herein, which may include one or more similar or different types of materials. In one example, as shown in  FIGS.  67 - 86   , the interior cavity  6810  may be filled with a filler material  7012 , which may be similar to the filler material  5112  or the filler material  5712 , or similar to any of the filler materials described herein or described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The filler material  7012  may be coupled to all or portions of the inner walls  6812  of the interior cavity  6810 . In one example, the filler material  7012  may have inherent adhesive or bonding properties to attach to all or portions of the inner walls  6812 . In another example, the filler material  7012  may be attached to all or portions of the inner walls  6812  with one or more bonding agents or adhesives that may be mixed with the filler material  7012 . In another example, the filler material  7012  may be attached to all or portions of the inner walls  6812  with one or more bonding agents or adhesives that may be separate from the filler material  7012 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the filler material  7012  may be coupled to at least a portion of the inner walls  6812  that may generally correspond to the ball strike region  6768  of the face portion  6762  (i.e., the filler material  7012  may be generally located behind the ball strike region  6768 ) or regions proximate to and/or surrounding the ball strike region  6768  of the face portion  6762 . In another example, the filler material  7012  may be coupled to at least 10% of the inner walls  6812 . In another example, the filler material  7012  may be coupled to at least 25% of the inner walls  6812 . In yet another example, the filler material  7012  may be coupled to between 25% and 50% of the inner walls  6812 . In another example, the filler material  7012  may be coupled to between 54% and 75% of the inner walls  6812 . In yet another example, the filler material  7012  may be coupled to between 50% and 90% of the inner walls  6812 . In yet another example, the filler material  7012  may be coupled to more than 75% of the inner walls  6812 . In yet another example, the filler material  7012  may be coupled to all of inner walls  6812 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The amount of the filler material  7012  that may be coupled to the inner walls  6812  may depend on the loft angle of the golf club head, the overall thickness of the face portion  6762 , the thickness profile of the face portion  6762 , the shape of the interior cavity  6810 , the locations and configurations of any ports or mass portions, and/or the material properties of the filler material  7012 . In one example, a golf club head with a relatively high loft angle may limit the portions of the inner walls  6812  to which the filler material  7012  may be coupled. In another example, a golf club head with a relatively small loft angle may allow the filler material  7012  to be coupled to all or substantial portions of the inner walls  6812 . In yet another example, the acoustic properties of a golf club head may be a factor in determining the amount of filler material  7012  that may be coupled to the inner walls  6812  to provide a pleasing sound and feel to an individual. The amount (i.e., volume and/or mass) of the filler material  7012  coupled to the inner walls  6812  may be determined for each golf club head (i.e., having a certain loft angle) to (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  6700  strikes a golf ball as perceived by an individual using the golf club head  6700 ), (ii) provide structural support for the face portion  6762 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  67 - 86   , a portion of the interior cavity  6810  including a central portion  6811  of the interior cavity  6810 , which may be a portion of the interior cavity  6810  that may generally correspond to the ball strike region  6768 , may be include the filler material  7012 . The width  6813  of the interior cavity  6810  at the central portion  6811  of the interior cavity  6810  may be generally greater than the width  6813  of the interior cavity  6810  at other portions of the interior cavity  6810 . Accordingly, the region of the interior cavity  6810  behind the ball strike region  6768 , i.e., the central portion  6811 , may include a relatively large volume of the filler material  7012 . Further, the configuration of the central portion  6811  (i.e., size, shape, contour, volume, etc.) may depend on the loft angle  7045 . For example, a golf club head  6700  with a relatively small loft angle  7045  may have a larger central portion  6811  (i.e., larger volume, depth, height, etc.) than a golf club head  6700  with a relatively large loft angle  7045 . Accordingly, as described herein, the amount of filler material  7012  inside the interior cavity  6810 , and more specifically, in the central portion  6811  may be determined based on the loft angle  7045  to provide (i) provide vibration dampening or sound dampening (e.g., consistent and/or pleasing sound and feel when the golf club head  6700  strikes a golf ball as perceived by an individual using the golf club head  6700 ), (ii) provide structural support for the face portion  6762 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The contour of the interior cavity  6810  or the shape of the inner walls  6812  may be defined by a plurality of recessed portions that are recessed relative to the perimeter edge portion  6761 . In the example of  FIGS.  67 - 86   , the interior cavity  6810  may include a first recessed portion  6814 , a second recessed portion  6815  that may have a generally smaller depth relative to the first recessed portion  6814 , a third recessed portion  6816  that may have a generally smaller depth than the second recessed portion  6815 , a fourth recessed portion  6817  that may have a generally smaller depth than the third recessed portion  6816 , and a fifth recessed portion  6818  that may have a generally smaller depth than the fourth recessed portion  6817 . The interior cavity  6810  may have more or less recessed portions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first recessed portion  6814  may generally include a largest width  6813  of the interior cavity  6810  and may be located at the central portion  6811  and/or may include portions that are adjacent to and/or surround the central portion  6811 . The second recessed portion  6815  may be adjacent to and/or surround all or portions of the first recessed portion  6814 , and may include portions that may be in the central portion  6811 . In the example of  FIGS.  67 - 86   , the second recessed portion  6815  is located below the first recessed portion  6814 . A portion of the structure of the body portion  6710  that includes the ports  6822 ,  6823 , and  6824  may be between the second recessed portion  6815  and the lower back wall portion  7114 . Accordingly, the depth of the second recessed portion  6815  may be less than the depth of the first recessed portion  6814  so that the body portion  6710  can accommodate the ports  6822 ,  6823 , and  6824  between the second recessed portion  6815  and the lower back wall portion  7114 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third recessed portion  6816  may be adjacent to and/or surround all or portions of the second recessed portion  6815  and/or the first recessed portion  6814 , and may include portions that may be in the central portion  6811 . In the example of  FIGS.  67 - 86   , the third recessed portion  6816  surrounds the first recessed portion  6814  above the horizontal midplane  7020 . The fourth recessed portion  6817  may be at or proximate to the perimeter edge portion  6761 , and/or may be adjacent to and/or surround all or portions of the third recessed portion  6816 , the second recessed portion  6815 , and/or the first recessed portion  6814 . In the example of  FIGS.  67 - 86   , the fourth recessed portion  6817  is adjacent to portions of the first recessed portion  6814  and the second recessed portion  6815  below the horizontal midplane  7020 . The fifth recessed portion  6818  may be adjacent to the perimeter edge portion  6761 . Accordingly, at any location in the interior cavity  6810  that includes the fifth recessed portion  6818 , the fifth recessed portion  6818  may be between the perimeter edge portion  6761  and any one or more of the first recessed portion  6814 , the second recessed portion  6815 , the third recessed portion  6816 , and the fourth recessed portion  6817 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  6810  may include one or more internal channels that may extend between the toe portion  6740  and the heel portion  6750 . In one example, as shown in  FIGS.  67 - 86   , the interior cavity  6810  may include a first internal channel  6825  that may extend from a location at the toe portion  6740  to the central portion  6811 , and a second internal channel  6826  that may extend from a location at the heel portion  6750  to the central portion  6811 . The first internal channel  6825  and the second internal channel  6826  connect to the first recessed portion  6814  and may have the same depth as the first recessed portion  6814  at or proximate to the central portion  6811 . The depths of the first internal channel  6825  and the second internal channel  6826  may diminish from the first recessed portion  6814  toward the toe portion  6740  and heel portion  6750 , respectively. As shown in the example of  FIGS.  67 - 86   , portions of the first internal channel  6825  and/or the second internal channel  6826  that connect to the first recessed portion  6814  and/or are proximate to the first recessed portion  6814  may maintain a constant depth that may be similar to the depth of the first recessed portion  6814 . Alternatively, all or portions of the first internal channel  6825  and/or the second internal channel  6826  may have diminishing depths in a direction toward the toe portion  6740  and the heel portion  6750 , respectively. For off-center hits of a golf ball with the face portion  6762 , the increased volume of the filler material  7012  in the internal channels  6825  and  6826  may (i) provide vibration dampening or sound dampening, (ii) provide structural support for the face portion  6762 , and/or (iii) optimize ball travel distance, ball speed, ball launch angle, ball spin rate, ball peak height, ball landing angle and/or ball dispersion. Further, the mass that is removed from the body portion  6710  to provide the internal channels  6825  and  6826  may be shifted to other locations on the body portion  6710  to increase and/or optimize the moment of inertia and the location of the center of gravity of the golf club head  6700 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  6810  may include additional recessed portions that may define transition regions between the first to fifth recessed portions  6814 - 6818  and the internal channels  6825  and  6826 . Each of the recessed portions may be adjacent to and transition into any one or several of the other recessed portions. For example, the first recessed portion  6814  may include an inclined surface  6827  (shown in  FIG.  71   ) that may transition and connect to the third recessed portion  6816  above the first recessed portion  6814 . Further, any of the recessed portions may directly transition to the perimeter edge portion  6761 . The recessed portions and the transition regions may collectively define the overall shape and/or contour of the interior cavity  6810 . The transition regions may include walls that are perpendicular, transverse, or include relative to adjacent recessed portions. Further, the transition regions may include rounded corners when joining an adjacent recessed portion to reduce stress concentrations at the joined corner. The recessed portions may define a contoured, continuous, and/or stepped reduction of the width of the interior cavity  6810  form the central portion  6811  to the perimeter edge portion  6761 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The shape, size, width, height, and other characteristics of the recessed portions  6814 - 6818  and the internal channels  6825  and  6826  may be associated with the loft angle  7045  of the golf club head  6700 . In one example, as shown in  FIGS.  67 - 86   , the first recessed portion  6814 , the second recessed portion  6815 , and the third recessed portion  6816  may be filled with the filler material  7012 . The filler material  7012  may be injection molded in the first recessed portion  6814 , the second recessed portion  6815 , and the third recessed portion  6816 . The filler material  7012  may be bonded to the inner walls  6812  of the first recessed portion  6814 , the second recessed portion  6815 , and the third recessed portion  6816  by having inherent adhesive or bonding properties, with a bonding agent that is mixed with the filler material  7012 , and/or a separate bonding agent. In another example, the filler material  7012  may be separately molded in the shape of the first recessed portion  6814 , the second recessed portion  6815 , and the third recessed portion  6816 , and coupled to the first recessed portion  6814 , the second recessed portion  6815 , and the third recessed portion  6816  with a bonding agent. In one example, the remaining portions of the interior cavity  6810 , which include the fourth recessed portion  6817  and the fifth recessed portion  6818  may be unfilled. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     A width of the filler material  7012  may vary from the toe portion  6740  to the heel portion  6750  and/or from the top portion  6780  to the sole portion  6790  and/or according to the shapes of the first recessed portion  6814 , the second recessed portion  6815 , the third recessed portion  6816 , the fourth recessed portion  6817 , the fifth recessed portion  6818  depending on the location inside the interior cavity  6810 , and/or similar to widths of any of the filler materials described herein. In one example, as shown in  FIGS.  67 - 86   , the filler material  7012  may be a filler insert  7320  having a width  7322  (W FI ) that may be similar or slightly greater than the width  6813  of the interior cavity  6810 . Accordingly, the filler insert  7320  may extend from the inner wall  6812  of the interior cavity  6810  to the back surface  6766  of the face portion  6762 . The filler insert  7320  may include a front surface  7330  and a back surface  7340 . The distance between the front surface  7330  and the back surface  7340  may define the width  7322  of the filler insert  7320 . The back surface  7340  may be coupled (i.e., contact, engage, attached, or bonded) to the inner walls  6812  of the interior cavity  6810 . To provide a continuous coupling or substantially continuous coupling between the filler insert  7320  and the inner walls  6812  of the interior cavity  6810 , the back surface  7340  may have a shape that corresponds or substantially corresponds to the shapes of portions of the inner walls  6812  of the interior cavity  6810  to which the filler insert  7320  may be coupled. Accordingly, as shown in the example of  FIG.  74   , the back surface  7340  may have a shape that may correspond to portions of the first recessed portion  6814 , the second recessed portion  6815 , the third recessed portion  6816 , the first internal channel  6825 , the second internal channel  6826 , and any inner wall transition portions (i.e., transition portions between recessed portions and/or channels) that the filler insert  7320  may be coupled. To provide a continuous coupling or substantially continuous coupling between the first filler insert  7320  and the back surface  6766  of the face portion  6762 , the front surface  7330  of the filler insert  7320  may have a shape that corresponds or substantially corresponds to the shape of the back surface  6766  of the face portion  6762 . In one example, as shown in  FIG.  73   , the front surface  7330  of the filler insert  7320  may be planar. In another example (not shown), the front surface  7330  may have groove, ridges, channels, slots, dimples, inverted cones, and/or various other shapes and contours that may resemble corresponding shapes of the back surface of the face portion  6762  and/or account for various thickness profiles of the face portion  6762  to provide continuous or substantially continuous coupling between the first filler insert  7320  and the face portion  6762 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The adhesive for bonding the filler insert  7320  to the inner walls  6812  of the interior cavity  6810  and to the back surface  6766  of the face portion  6762  may be similar to any of the adhesive or bonding agents described herein. In one example, the adhesives for bonding the filler insert  7320  to the inner walls  6812  of the interior cavity  6810  and to the back surface  6766  of the face portion  6762  may be similar. In another example, the adhesive for bonding the filler insert  7320  to the inner walls  6812  of the interior cavity  6810  and to the back surface  6766  of the face portion  6762  may be different to account for the different materials of the body portion  6710  and the face portion  6762 . In yet another example, the adhesive for bonding the filler insert  7320  to the inner walls  6812  of the interior cavity  6810  and the back surface  6766  of the face portion  6762  may be similar to the second filler material  4213 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIGS.  75 - 78   , another filler insert  7420  having a front surface  7430  and a back surface  7440  may be similar in many respects to the filler insert  7320  as described herein. The filler insert  7420  may include and upper slot  7450 , which may be U-shaped. Accordingly, the upper slot  7450  may include a first arm  7452  and a second arm  7454 . The first arm  7452  may be coupled to the back surface  6766  of the face portion  6762 . The second arm  7454  may be coupled to the inner walls  6812  of the interior cavity  6810 . When the face portion  6762  strikes a golf ball, the first arm  7452  may both compress and deflect toward the second arm  7454  to allow for the corresponding upper portion of the face portion  6762  to have a larger deflection than the lower portion of the face portion  6762 . Accordingly, the upper portion of the face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics than the lower portion of the face portion  6762 . Further, the filler insert  7420  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  79   , another filler insert  7920  having a front surface  7930  and a back surface  7940  may be similar in many respects to the filler insert  7320  as described herein. The filler insert  7920  may include a lower slot  7950 , which may be U-shaped. Accordingly, the lower slot  7950  may include a first arm  7952  and a second arm  7954 . The first arm  7952  may be coupled or bonded to the back surface  6766  of the face portion  6762  as described herein. The second arm  7954  may be coupled to the inner walls  6812  of the interior cavity  6810  as described herein. When the face portion  6762  strikes a golf ball, the first arm  7952  may both compress and deflect toward the second arm  7954  to allow for the corresponding lower portion of the face portion  6762  to have a larger deflection than the upper portion of the face portion  6762 . Accordingly, the lower portion of the face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics than the upper portion of the face portion  6762 . Further, the filler insert  7920  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  80   , another filler insert  8020  having a front surface  8030  and a back surface  8040  may be similar in many respects to the filler insert  7320  as described herein. The filler insert  8020  may include a front cavity  8050  at the front surface  8030 . Accordingly, the front surface  8030  may include an upper front surface  8031  coupled or bonded to the back surface  6766  of the face portion  6762  and a lower front surface  8032  coupled or bonded to the back surface  6766  of the face portion  6762 . As shown in the example of  FIG.  80   , the front cavity  8050  may have a circular shape. In another example (not shown), the front cavity  8050  may have a non-circular shape. In one example, as shown in  FIG.  80   , the front cavity  8050  may be behind a central portion of the face portion  6762 , which may correspond to a general ball strike region of the face portion  6762 . When the face portion  6762  strikes a golf ball, the central portion of the face portion  6762  may have a larger deflection than the surrounding portions of the face portion  6762 . Accordingly, the central portion of the face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics than the surrounding portions the face portion  6762 . Further, the filler insert  8020  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  81   , another filler insert  8120  having a front surface  8130  and a back surface  8140  may be similar in many respects to the filler insert  7320  as described herein. The filler insert  8120  may include an upper slot  8150  and a lower slot  8152  to define a center portion  8153 . The center portion  8153  defines a portion of the front surface  8130  that may be coupled or bonded to the back surface  6766  of the face portion  6762 . The area of the center portion  8153  that is coupled or bonded to the face portion  6762  may have any shape such as circular, rectangular, or square. The center portion  8153  may be behind a central portion of the face portion  6762 , which may correspond to a general ball strike region of the face portion  6762 . When the face portion  6762  strikes a golf ball, the center portion  8153  of the filler insert  8120  may deflect along with the central portion of the face portion  6762 . Accordingly, the central portion of the face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics than the surrounding portions the face portion  6762 . Further, the filler insert  8120  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  82   , another filler insert  8220  having a front surface  8230  and a back surface  8240  may be similar in many respects to the filler insert  7320  as described herein. The filler insert  8220  may include a front cavity  8250  at the front surface  8230 . Accordingly, the front surface  8230  may include an upper front surface  8231  coupled or bonded to the back surface  6766  of the face portion  6762  and a lower front surface  8232  coupled or bonded to the back surface  6766  of the face portion  6762 . As shown in the example of  FIG.  82   , the front cavity  8250  may have a rectangular shape. In another example (not shown), the front cavity  8250  may have a non-rectangular shape. In one example, as shown in  FIG.  82   , the front cavity  8250  may be behind a central portion of the face portion  6762 , which may correspond to a ball strike region of the face portion  6762 . When the face portion  6762  strikes a golf ball, the central portion of the face portion  6762  may have a larger deflection than the surrounding portions of the face portion  6762 . Accordingly, the central portion of the face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics than the surrounding portions the face portion  6762 . Further, the filler insert  8220  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  83   , another filler insert  8320  having a front surface  8330  and a back surface  8340  may be similar in many respects to the filler insert  7320  as described herein. The filler insert  8320  may have a height  8321  that may be smaller than the height of the filler insert  7320 . Accordingly, the front surface  8330  may be coupled or bonded to a smaller area of the face portion  6762 . As a result, the face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics than the surrounding portions the face portion  6762  as compared to a golf club head having the filler insert  7320 . Further, the filler insert  8320  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  84   , another filler insert  8420  having a front surface  8430  and a back surface  8440  may be similar in many respects to the filler insert  7320  as described herein. The filler insert  8420  may have a height  8421  that may be smaller than the height of the filler insert  7320  and smaller than the height  8321  of the filler insert  8320 . Accordingly, the front surface  8430  may be coupled or bonded to a smaller area of the face portion  6762 . As a result, the face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics than the surrounding portions the face portion  6762  as compared to a golf club head having the filler insert  7320  or a golf club head having the filler insert  8320 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  85   , another filler insert  8520  having a front surface  8530  and a back surface  8540  may be similar in many respects to the filler insert  7320  as described herein. The front surface  8530  of the filler insert  8520  may be bonded or coupled to the face portion  6762 . The back surface  8540  of the filler insert  8520  may not be coupled to the inner walls  6812  of the interior cavity  6810 . The filler insert  8520  may have any cross-sectional shape. In the example of  FIG.  85   , the filler insert  8520  may have a width  8523  that increases linearly or substantially linearly in a direction from the top portion  6780  to a location behind a central portion of the face portion  6762 , and decreases linearly from the location behind the central portion of the face portion  6762  in a direction toward the sole portion  6790 . The face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics at different locations on the face portion  6762  that may correspond with the cross-sectional shape of the filler insert  8520 . Further, the filler insert  8520  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  86   , another filler insert  8620  having a front surface  8630  and a back surface  8640  may be similar in many respects to the filler insert  7320  as described herein. The front surface  8630  of the filler insert  8620  may be bonded or coupled to the face portion  6762 . The back surface  8640  of the filler insert  8520  may not be coupled to the inner walls  6812  of the interior cavity  6810 . The filler insert  8620  may have any cross-sectional shape. In the example of  FIG.  86   , the filler insert  8620  may have a width  8623  that increases in a curved manner or path in a direction from the top portion  6780  to a location behind a central portion of the face portion  6762 , and decreases in a curved manner or path from the location behind the central portion of the face portion  6762  in a direction toward the sole portion  6790 . The face portion  6762  may exhibit different ball spin, launch angle, launch speed, and/or trajectory characteristics that may correspond to cross-sectional shape of the filler insert  8620 . Further, the filler insert  8620  may absorb shock, isolate vibration, and/or dampen noise when the face portion  6762  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example (not shown), the interior cavity  6810  may be entirely filled with the filler material  7012 . In another example, as shown in  FIGS.  67 - 86   , the interior cavity  6810  may be partially filled with the filler material  7012 , and the remaining portions of the interior cavity  6810  may be unfilled. In another example (not shown), the remaining portions of the interior cavity  6810  may be filled with another filler material that may be similar to any of the filler materials described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the cross-sectional shape of any of the filler inserts shown in  FIGS.  67 - 86    may extend the entire distance inside the interior cavity  6810  between the toe portion  6740  and the heel portion  6750 . In another example, the cross-sectional shape of a filler insert may extend along one or more portions of the distance inside the interior cavity  6810  between the toe portion  6740  and the heel portion  6750 . In another example, the cross-sectional shape of a filler insert may extend along a portion of the interior cavity  6810  behind a central portion or the strike region of the face portion  6762 . In yet another example, the cross-sectional shape of a filler insert may extend a certain portion of the interior cavity  6810  according to one of the configurations described herein, and the cross sectional shape of the filler insert at other portions of the interior cavity  6810  may be configured according to one or more of the other cross-sectional configurations of the filler insert described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Any of the filler inserts described herein may be attached or bonded to the inner walls  6812  of the interior cavity  6810  by any of adhesive or bonding agents described herein. In another example, one or more portions of the interior cavity  6810  that may not be occupied by the filler insert  8020  may be filled with any of the filler materials described herein. In another example, the interior cavity  6810  may only include a filler insert as described herein. In yet another example, interior cavity  6810  may be partially or fully filled with any of the filler materials described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
       FIG.  87    depicts one manner by which the golf club head  6700  or any of the golf club heads described herein may be manufactured. In the example of  FIG.  87   , the process  8700  may begin with providing a body portion  6710  and a face portion  6762  of a golf club head  6700  (block  8710 ). The filler insert  7320  may be formed by injection molding the filler material  7012  in a mold that is configured to produce a filler insert  7320  as described herein (block  8720 ). For example, the interior of the mold may include portions that correspond in shape to portions of the interior cavity  6810  to which the filler insert  7320  may be coupled as described herein. The filler insert  7320  may then be attached to the inner walls  6812  of the interior cavity  6810  as described herein (block  8730 ). The face portion  6762  may then be attached to the body portion  6710  as described herein to enclose the interior cavity  6810  (block  8740 ). In one example, prior to attaching the face portion  6762  to the body portion  6710 , an adhesive or a bonding agent may be applied to portions of the back surface  6766  of the face portion  6762  that couples to the filler insert  7320 . In another example, the filler insert  7320  may engage the back surface  6766  of the face portion  6762  without the use of any adhesives or bonding agents. Alternatively, the filler insert  7320  may be attached to the back surface  6766  of the face portion  6762  (block  8730 ). In one example, prior to attaching the face portion  6762  to the body portion  6710 , an adhesive or a bonding agent may be applied to portions of the inner walls  6812  of the interior cavity  6810  that couples to the filler insert  7320 . In another example, the filler insert  7320  may engage the inner walls  6812  of the interior cavity  6810  without the use of any adhesives or bonding agents. The filler insert  7320  may be slightly compressed between the inner walls  6812  of the interior cavity  6810  and the back surface  6766  of the face portion  6762  after the face portion  6762  is attached to the body portion  6710 . The slight compression of the filler insert  7320  may assist in maintaining the filler insert  7320  engaged to the inner walls  6812  of the interior cavity  6810  and/or the back surface  6766  of the face portion  6762  with or without the use of adhesives or bonding agents. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  88   , a face portion  8862  may have a first thickness  8810  (T1) or a second thickness  8820  (T2). The first thickness  8810  may be a thickness of a section of the face portion  8862  adjacent to a groove  8868  whereas the second thickness  8820  may be a thickness of a section of the face portion  8862  below the groove  8868 . For example, the first thickness  8810  may be a maximum distance between the front surface  8864  and the back surface  8866 . The second thickness  8820  may be based on the groove  8868 . In particular, the groove  8868  may have a groove depth  8825  (Dgroove). The second thickness  8820  may be a maximum distance between the bottom of the groove  8868  and the back surface  8866 . The sum of the second thickness  8820  and the groove depth  8825  may be substantially equal to the first thickness  8810  (e.g., T2+Dgroove=T1). Accordingly, the second thickness  8820  may be less than the first thickness  8810  (e.g., T2&lt;T1). 
     To lower and/or move the CG of a golf club head further back, such as the CG of any of the golf club heads described herein, mass from the front portion of a golf club head may be removed by using a relatively thinner face portion  8862 . For example, the first thickness  8810  or the second thickness  8820  may be less than or equal to 0.1 inch (2.54 millimeters). In another example, the first thickness  8810  or the second thickness  8820  may be about 0.075 inch (1.875 millimeters) (e.g., T1=0.075 inch). With the support of the back wall portion of a golf club head to form an interior cavity and filling at least a portion of the interior cavity with one or more filler materials as described herein, the face portion  8862  may be relatively thinner (e.g., T1&lt;0.075 inch) without degrading the structural integrity, sound, and/or feel of a golf club head. In one example, the first thickness  8810  may be less than or equal to 0.060 inch (1.524 millimeters) (e.g., T1≤0.060 inch). In another example, the first thickness  8810  may be less than or equal to 0.040 inch (1.016 millimeters) (e.g., T1≤0.040 inch). Based on the type of material(s) used to form the face portion  8862  and/or the body portion  110 , the face portion  8862  may be even thinner with the first thickness  8810  being less than or equal to 0.030 inch (0.762 millimeters) (e.g., T1≤0.030 inch). The groove depth  8825  may be greater than or equal to the second thickness  8820  (e.g., Dgroove≥T2). In one example, the groove depth  8825  may be about 0.020 inch (0.508 millimeters) (e.g., Dgroove=0.020 inch). Accordingly, the second thickness  8820  may be about 0.010 inch (0.254 millimeters) (e.g., T2=0.010 inch). In another example, the groove depth  8825  may be about 0.015 inch (0.381 millimeters), and the second thickness  8820  may be about 0.015 inch (e.g., Dgroove=T2=0.015 inch). Alternatively, the groove depth  8825  may be less than the second thickness  8820  (e.g., Dgroove&lt;T2). Without the support of the back wall portion of a golf club head and one or more filler materials used to fill in the interior cavity, the golf club head may not be able to withstand multiple impacts by a golf ball on a face portion. In contrast, a golf club head with a relatively thin face portion but without the support of the back wall portion and the one or more filler materials as described herein (e.g., a cavity-back golf club head) may produce unpleasant sound (e.g., a tinny sound) and/or feel during impact with a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Based on manufacturing processes and methods used to form a golf club head such as any of the golf club heads described herein, the face portion  8862  may include additional material at or proximate to a periphery of the face portion  8862 . Accordingly, the face portion  8862  may also include a third thickness  8830 , and a chamfer portion  8840 . The third thickness  8830  may be greater than either the first thickness  8810  or the second thickness  8820  (e.g., T3&gt;T1&gt;T2). In particular, the face portion  8862  may be coupled to the body portion of a golf club head by a welding process. For example, the first thickness  8810  may be about 0.030 inch (0.762 millimeters), the second thickness  8820  may be about 0.015 inch (0.381 millimeters), and the third thickness  8830  may be about 0.050 inch (1.27 millimeters). Accordingly, the chamfer portion  8840  may accommodate some of the additional material when the face portion  8862  is welded to the body portion of the golf club head. 
     As illustrated in  FIG.  89   , for example, the face portion  8862  may include a reinforcement section, generally shown as  8905 , below one or more grooves  8868 . In one example, the face portion  8862  may include a reinforcement section  8905  below each groove. Alternatively, face portion  8862  may include the reinforcement section  8905  below some grooves (e.g., every other groove) or below only one groove. The face portion  8862  may include a first thickness  8910 , a second thickness  8920 , a third thickness  8930 , and a chamfer portion  8940 . The groove  8868  may have a groove depth  8925 . The reinforcement section  8905  may define the second thickness  8920 . The first and second thicknesses  8910  and  8920 , respectively, may be substantially equal to each other (e.g., T1=T2). In one example, the first and second thicknesses  8910  and  8920 , respectively, may be about 0.030 inch (0.762 millimeters) (e.g., T1=T2=0.030 inch). The groove depth  8925  may be about 0.015 inch (0.381 millimeters), and the third thickness  8930  may be about 0.050 inch (1.27 millimeters). The groove  8868  may also have a groove width. The width of the reinforcement section  8905  may be greater than or equal to the groove width. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Alternatively, the face portion  8862  may vary in thickness at and/or between the top portion and the sole portion of a golf club head. In one example, the face portion  8862  may be relatively thicker at or proximate to the top portion than at or proximate to the sole portion (e.g., thickness of the face portion  8862  may taper from the top portion towards the sole portion). In another example, the face portion  8862  may be relatively thicker at or proximate to the sole portion than at or proximate to the top portion (e.g., thickness of the face portion  8862  may taper from the sole portion towards the top portion). In yet another example, the face portion  8862  may be relatively thicker between the top portion and the sole portion than at or proximate to the top portion and the sole portion (e.g., thickness of the face portion  8862  may have a bell-shaped contour). The face portion  8862  may be similar to any of the face portions described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     One or more mass portions of any of the sets of mass portions described herein may have similar or different physical properties (e.g., color, marking, shape, size, density, mass, volume, external surface texture, materials of construction, etc.). Accordingly, any of the sets of mass portions described herein may contribute to the ornamental design of a golf club head. In the illustrated example as shown in  FIG.  90   , one or more mass portions of any of the sets of mass portions described herein may have a cylindrical shape (e.g., a circular cross section). Alternatively, one or more mass portions of any of the sets of mass portions described herein may have a first shape (e.g., a cylindrical shape) whereas one or more mass portions of another one of the sets of mass portions as described herein may have a second shape (e.g., a cubical shape). In another example, one or more mass portions of any of the sets of mass portions described herein may include two or more mass portions with different shapes. In another example, one or more mass portions of any of the sets of mass portions described herein may have a different color(s), marking(s), shape(s), density or densities, mass(es), volume(s), material(s) of construction, external surface texture(s), and/or any other physical property as compared to one or more mass portions of another one of the sets of mass portions as described herein. The properties of any of the mass portions and sets of mass portions described herein may be similar to any of the mass portions and sets of mass portions described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Referring to  FIGS.  91  and  92   , for example, a first mass portion  9100  and a second mass portion  9200  may include threads, generally shown as  9110  and  9210 , respectively, to engage with correspondingly configured threads in ports on the to secure in the ports as described herein. Accordingly, one or more mass portions as described herein may be shaped similar to and function as a screw or threaded fastener for engaging threads in a port. For example, one or more mass portions of any of the sets of mass portions described herein may be a screw. One or more mass portions of any of the mass portions described herein may not be readily removable from the body portion of a golf club head with or without a tool. Alternatively, one or more mass portions of any of the sets of mass portions described herein may be readily removable (e.g., with a tool) so that a relatively heavier or lighter mass portion may replace one or more mass portions of any of the sets of mass portions described herein. In another example, one or more mass portions of any of the sets of mass portions described herein may be secured in the ports with epoxy or adhesive so that the mass portions may not be readily removable. In yet another example, one or more mass portions of any of the sets of mass portions described herein may be secured in the ports with both threads and thread sealant (e.g. acrylic adhesive, cyanoacrylate adhesive, epoxy, thermoplastic adhesive, silicone sealant, or urethane adhesive) so that the mass portions may not be readily removable. In yet another example, one or more mass portions of any of the sets of mass portions described herein may be press fit in a port. In yet another example, one or more mass portions of any of the sets of mass portions described herein may be formed inside a port by injection molding. For example, a liquid metallic material (i.e., molten metal) or a plastic material (e.g. rubber, foam, or any polymer material) may be injected or otherwise introduced into a port. After the liquid material is cooled and/or cured inside the port, the resulting solid material (e.g., a metal material, a plastic material, or a combination thereof) may form a mass portion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As mentioned above, one or more mass portions of any of the sets of mass portions described herein may be similar in some physical properties but different in other physical properties. For example, a mass portion may be made from an aluminum-based material or an aluminum alloy whereas another mass portion may be made from a tungsten-based material or a tungsten alloy. In another example, a mass portion may be made from a polymer material whereas another mass portion may be made from a steel-based material. In yet another example, as illustrated in  FIGS.  90 - 92   , one or more mass portions of any of the sets of mass portions described herein may have a diameter  9010  of about 0.25 inch (6.35 millimeters) but one or more mass portions of another one or more sets of mass portions described herein may be different in height. In particular, one or more mass portions of any of the sets of mass portions described herein may be associated with a first height  9120 , and one or more mass portions of another one or more sets of mass portions described herein may be associated with a second height  9220 . The first height  9120  may be relatively shorter than the second height  9220 . In one example, the first height  9120  may be about 0.125 inch (3.175 millimeters) whereas the second height  9220  may be about 0.3 inch (7.62 millimeters). In another example, the first height  9120  may be about 0.16 inch (4.064 millimeters) whereas the second height  9220  may be about 0.4 inch (10.16 millimeters). Alternatively, the first height  9120  may be equal to or greater than the second height  9220 . Although the above examples may describe particular dimensions, one or more mass portions described herein may have different dimensions. In one example, any of the mass portions described herein may be interchangeably used in any of the ports described herein. Any property of any of the mass portions described herein may be similar to the corresponding property of any of the mass portions described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The apparatus, methods, and articles of manufacture described herein may include one or more club identifiers (e.g., a serial number, a matrix barcode, a trademark, a club number, a loft angle, a character, etc.). For example, any of the golf club heads described herein may include a visual indicator such as a club number to identify the type of golf club. In particular, the club number may correspond to the loft angle of the golf club head (e.g., 3, 4, 5, 6, 7, 8, or 9). In one example, a 7-iron type golf club head may be marked with “7”. In another example, a golf club head may be marked with the loft angle. For example, a 54-degree wedge type golf club head may be marked “54”. In yet another example, a 10.5-degree driver type golf club head may be marked “10.5.” Any marking(s) associated with a club identifier may be visually differentiated (e.g., different color, texture, pattern, etc.) from the rest of a golf club head. To distinguish from other golf club heads, a golf club head as described herein may include a trademark (e.g., a word, a name, a symbol, a design, or any combination thereof) to identify a brand name or a model of the golf club head (e.g., distinguish from other manufacturer or seller). The club identifier may be another type of visual indicator such as a product number or a serial number to identify the golf club head as authentic equipment, to track inventory, or to distinguish the golf club head from fake or counterfeit products. Alternatively, the club identifier may be a digital signature or a machine-readable optical representation of information or data about the golf club head (e.g., numeric character(s), alphanumeric character(s), byte(s), a one-dimensional barcode such as a Universal Product Code (UPC), a two-dimensional barcode such as a Quick Response (QR) code, etc.). The club identifier may be placed at various location on the golf club head (e.g., the heel portion, the hosel portion, the face portion, the top portion, the sole portion, etc.) using various methods (e.g., painted, laser etched, stamped, casted, or molded onto the golf club head). For example, the club identifier may be a serial number laser etched onto the hosel portion of the golf club head. Instead of being an integral part of the golf club head, the club identifier may be a separate component coupled to the golf club head (e.g., a label adhered via an adhesive or an epoxy). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     To determine the effect of using different filler materials on the coefficient of restitution (COR) and the performance of the golf club head  5400 , several golf clubs having golf club heads that were similar to the golf club head  5400  but with different loft configurations (i.e., 4-iron, 7-iron, pitching wedge) and different filler materials were tested to obtain COR, ball speed, launch angle, back spin, peak height, and carry distance for each golf club. To measure the COR of each golf club, an air cannon device was used to launch a golf ball weighing approximately 45 grams at an initial velocity (i.e., inbound velocity) of about 125 mph toward a center location (as defined below) of the golf club head for multiple iterations. A speed monitoring device was used to measure the outbound velocity (mph) and the rebound time in milliseconds (ms) of the golf ball for each test iteration. An average COR of the golf club head was then determined from the measured data. To measure ball speed, launch angle, back spin, peak height, and carry distance for each golf club, each of the example golf clubs was tested with a swing robot manufactured by Golf Laboratories of San Diego, Calif. to strike a golf ball at an average golf club head speed of 84 mph to 86 mph for multiple iterations at each of five locations on the face portion of the golf club head to determine average ball speed (mph), average ball launch angle (radians), average ball back spin (rpm), average ball peak height (yards), and average total carry distance (yards). The five locations of the face portion were a center location, a toe location, a heel location, a low location, and a high location. The center location was determined as the location on the face portion by which a golf ball is typically struck by an individual. In other words, the center location statistically (e.g., greater than 75%) receives the highest number of ball strikes. The center location was determined to be at 0.75 inches or approximately 0.75 inches up from the bottom portion and at the center of a corresponding groove on the face portion subject to variations and/or approximations according to measurement tolerances and/or the actual ball strike region on the face portion by the swing robot. The toe location and the heel location were determined as 0.5 inches or approximately 0.5 inches from the center location in the toe direction and in the heel direction, respectively, subject to variations and/or approximations according to measurement tolerances and the actual ball strike point on the face portion by the swing robot. The high location and the low location were determined as 0.25 inches or approximately 0.25 inches from the center location in the top direction and the bottom direction, respectively, subject to variations and/or approximations according to measurement tolerances and the actual ball strike point on the face portion by the swing robot. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Tables 5-10 show experimental performance results for three examples of a 4-iron golf club having a golf club head constructed according to apparatus, methods, and articles of manufacture described herein for the golf club head  5400  with each example having different filler materials. The golf club head  5491  (not shown) of example 1 was similar to the golf club head  5400  in a 4-iron configuration except that the golf club head  5491  was filled with a thermoplastic elastomer (TPE) filler material with the same or similar properties as any of the TPE materials described herein or in any of the incorporated by reference applications. The golf club head  5494  (not shown) of example 2 was similar to the golf club head  5400  in a 4-iron configuration except that the golf club head  5494  was filled with an epoxy material with the same or similar properties as any of the epoxy materials described herein or in any of the incorporated by reference applications. The golf club head  5493  of example 3 was similar to the golf club head  5400  in a 4-iron configuration and was filled with the first filler material  5712  and the second filler material  5714  as described in detail herein. Accordingly, all three example golf club heads  5491 ,  5494 , and  5493  were structurally similar except for the differences in their filler materials. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 4-Iron Golf Club COR at Face Center Location 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Inbound 
                 Outbound 
                 Rebound 
                   
               
               
                   
                 Velocity 
                 Velocity 
                 Time 
               
               
                 Golf Club Head 
                 (mph) 
                 (mph) 
                 (ms) 
                 COR 
               
               
                   
               
               
                 Golf Club Head 5491 
                 125.01 
                 64.75 
                 23.59 
                 0.803 
               
               
                 Golf Club Head 5492 
                 124.96 
                 65.90 
                 23.32 
                 0.814 
               
               
                 Golf Club Head 5493 
                 124.97 
                 66.92 
                 23.13 
                 0.824 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 4-Iron Golf Club Ball Speed (mph) vs. Face Portion Location 
               
            
           
           
               
               
            
               
                   
                 Face Location 
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 5491 
                 126.63 
                 123.45 
                 124.62 
                 121.32 
                 126.65 
               
               
                 Golf Club Head 5492 
                 127.52 
                 124.18 
                 124.97 
                 122.93 
                 125.73 
               
               
                 Golf Club Head 5493 
                 127.95 
                 124.33 
                 125.03 
                 123.42 
                 126.42 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 4-Iron Golf Club Launch Angle (radians) vs. Face Portion Location 
               
            
           
           
               
               
            
               
                   
                 Face Location 
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 5491 
                 13.93 
                 14.02 
                 13.60 
                 14.27 
                 13.58 
               
               
                 Golf Club Head 5492 
                 13.90 
                 13.88 
                 13.47 
                 14.33 
                 13.37 
               
               
                 Golf Club Head 5493 
                 14.05 
                 14.20 
                 13.92 
                 14.23 
                 13.63 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 4-Iron Golf Club Backspin (rpm) vs. Face Portion Location 
               
            
           
           
               
               
            
               
                   
                 Face Location 
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 5491 
                 3695 
                 3839 
                 3589 
                 3764 
                 3942 
               
               
                 Golf Club Head 5492 
                 3826 
                 3931 
                 3696 
                 3899 
                 3924 
               
               
                 Golf Club Head 5493 
                 3765 
                 3925 
                 3689 
                 3865 
                 3988 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 4-Iron Golf Club Peak Height (yards) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 28.00 
                 26.17 
                 25.83 
                 25.50 
                 27.00 
               
               
                 5491 
               
               
                 Golf Club Head 
                 28.00 
                 26.67 
                 26.00 
                 27.00 
                 26.17 
               
               
                 5492 
               
               
                 Golf Club Head 
                 28.83 
                 27.00 
                 26.67 
                 27.00 
                 27.33 
               
               
                 5493 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 4-Iron Golf Club Carry Distance (yards) vs. Face Portion Location 
               
            
           
           
               
               
            
               
                   
                 Face Location 
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 210.33 
                 202.33 
                 207.00 
                 199.00 
                 207.50 
               
               
                 5491 
               
               
                 Golf Club Head 
                 210.67 
                 203.17 
                 206.00 
                 201.00 
                 205.50 
               
               
                 5492 
               
               
                 Golf Club Head 
                 211.83 
                 203.33 
                 207.00 
                 202.67 
                 206.67 
               
               
                 5493 
               
               
                   
               
            
           
         
       
     
     Referring to Table 5, the golf club head  5493  has a higher COR for face center strikes than the golf club heads  5491  and  5494 . Accordingly, as shown in Table 6, the higher COR provides a higher ball speed than golf club heads  5491  and  5494  at the center location. In particular, at the center location, the increase in ball speed for the golf club head  5493  relative to the golf club head  5494  is close to 0.5 mph, and the increase in ball speed for the golf club head  5493  relative to the golf club head  5491  is more than one (1) mph and close to 1.5 mph. With reference to Table 10, the increase in ball speed at the center location for the golf club head  5493  relative to the golf club heads  5491  and  5494  provides a greater total ball carry distance for the golf club head  5493 . In particular, at the center location, the increase in carry distance for the golf club head  5493  relative to the golf club head  5494  is over one (1) yard, and the increase in carry distance for the golf club head  5493  relative to the golf club head  5491  is 1.5 yards. As described herein, the center location of the face portion may represent the highest statistical strike region on the face portion. In other words, many individuals may strike a golf ball at or proximate to the center location. Accordingly, the golf club head  5493  as described in detail herein (e.g., filled with the first and second filler materials  5712  and  5714 , respectively) provides improved performance for all face center strikes in comparison to a golf club head that is similar to the golf club head  5400  but filled with another filler material such as a TPE material (e.g., the golf club head  5491 ) or an epoxy material (e.g., the golf club head  5494 ). Further, the ball speed and carry distance for the golf club head  5493  at the heel, the toe, and the high face locations are greater than the ball speed and carry distance for the same locations, respectively, for the golf club heads  5491  and  5494 . Accordingly, the golf club head  5493  as described in detail herein (e.g., filled with the first and second filler materials  5712  and  5714 , respectively) provides an overall improved performance in comparison to a golf club head that is similar to the golf club head  5400  but filled with another filler material such as a TPE material (e.g., the golf club head  5491 ) or an epoxy material (e.g., the golf club head  5494 ). 
     Tables 11-16 show experimental performance results for three examples of a 7-iron golf club having a golf club head constructed according to apparatus, methods, and articles of manufacture described herein for the golf club head  5400  with each example having different filler materials. The golf club head  5591  (not shown) of example 4 was similar to the golf club head  5400  in a 7-iron configuration except that the golf club head  5591  was filled with a thermoplastic elastomer (TPE) filler material with the same or similar properties as any of the TPE materials described herein or in any of the incorporated by reference applications. The golf club head  5592  (not shown) of example 5 was similar to the golf club head  5400  in a 7-iron configuration except that the golf club head  5592  was filled with an epoxy material with the same or similar properties as any of the epoxy materials described herein or in any of the incorporated by reference applications. The golf club head  5593  of example 6 was similar to the golf club head  5400  in a 7-iron configuration and was filled with the first filler material  5712  and the second filler material  5714  as described in detail herein. Accordingly, all three example golf club heads  5591 ,  5592 , and  5593  were structurally similar except for the differences in their filler materials. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 7-Iron Golf Club COR at Face Center Location 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Inbound 
                 Outbound 
                 Rebound 
                   
               
               
                   
                 Golf Club 
                 Velocity 
                 Velocity 
                 Time 
               
               
                   
                 Head 
                 (mph) 
                 (mph) 
                 (ms) 
                 COR 
               
               
                   
                   
               
               
                   
                 Golf Club 
                 124.88 
                 67.98 
                 22.96 
                 0.808 
               
               
                   
                 Head 5591 
               
               
                   
                 Golf Club 
                 125.25 
                 68.61 
                 22.79 
                 0.811 
               
               
                   
                 Head 5592 
               
               
                   
                 Golf Club 
                 125.13 
                 69.75 
                 22.58 
                 0.821 
               
               
                   
                 Head 5593 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 7-Iron Golf Club Ball Speed (mph) vs. Face Portion Location 
               
            
           
           
               
               
            
               
                   
                 Face Location 
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 115.90 
                 114.00 
                 113.70 
                 113.90 
                 112.60 
               
               
                 5591 
               
               
                 Golf Club Head 
                 115.52 
                 113.44 
                 113.12 
                 111.89 
                 111.75 
               
               
                 5592 
               
               
                 Golf Club Head 
                 116.70 
                 113.90 
                 114.30 
                 114.00 
                 112.90 
               
               
                 5593 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 7-Iron Golf Club Launch Angle (radians) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 18.40 
                 18.30 
                 18.00 
                 17.90 
                 17.70 
               
               
                 5591 
               
               
                 Golf Club Head 
                 18.28 
                 17.97 
                 18.26 
                 18.82 
                 17.45 
               
               
                 5592 
               
               
                 Golf Club Head 
                 17.80 
                 17.30 
                 17.30 
                 18.00 
                 17.20 
               
               
                 5593 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 7-Iron Golf Club Backspin (rpm) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 5354 
                 5534 
                 5045 
                 5298 
                 5761 
               
               
                 5591 
               
               
                 Golf Club Head 
                 5796 
                 5927 
                 5495 
                 5836 
                 6032 
               
               
                 5592 
               
               
                 Golf Club Head 
                 5534 
                 5824 
                 5469 
                 5597 
                 5784 
               
               
                 5593 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 15 
               
             
            
               
                   
               
               
                 7-Iron Golf Club Peak Height (yards) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 31.00 
                 30.00 
                 29.00 
                 29.00 
                 28.00 
               
               
                 5591 
               
               
                 Golf Club Head 
                 31.00 
                 29.10 
                 29.10 
                 29.60 
                 27.30 
               
               
                 5592 
               
               
                 Golf Club Head 
                 31.00 
                 28.00 
                 28.00 
                 29.00 
                 28.00 
               
               
                 5593 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 16 
               
             
            
               
                   
               
               
                 7-Iron Golf Club Carry Distance (yards) vs. Face Portion Location 
               
            
           
           
               
               
            
               
                   
                 Face Location 
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 177.00 
                 173.00 
                 176.00 
                 174.00 
                 170.00 
               
               
                 5591 
               
               
                 Golf Club Head 
                 174.50 
                 170.20 
                 172.00 
                 168.20 
                 166.90 
               
               
                 5592 
               
               
                 Golf Club Head 
                 178.00 
                 172.00 
                 174.00 
                 173.00 
                 170.00 
               
               
                 5593 
               
               
                   
               
            
           
         
       
     
     Referring to Table 11, the golf club head  5593  has a higher COR for face center strikes than the golf club heads  5591  and  5592 . Accordingly, as shown in Table 12, the golf club head  5593  provides a higher ball speed than golf club heads  5591  and  5592  at the center location. In particular, at the center location, the increase in ball speed for the golf club head  5593  relative to the golf club head  5591  is close to one (1) mph, and the increase in ball speed for the golf club head  5593  relative to the golf club head  5592  is more than one (1) mph. With reference to Table 16, the increase in ball speed at the center location of the golf club head  5593  provides a greater total ball carry distance for the golf club head  5593  in comparison to the golf club head  5591  and the golf club head  5592 . In particular, at the center location, the increase in carry distance for the golf club head  5593  relative to the golf club head  5591  is one (1) yard, and the increase in carry distance for the golf club head  5593  relative to the golf club head  5592  is over three (3) yards. As described herein, the center location of the face portion may represent the highest statistical strike region on the face portion. In other words, many individuals may strike a golf ball at or proximate to the center location. Accordingly, the golf club head  5593  as described in detail herein (e.g., filled with the first and second filler materials  5712  and  5714 , respectively) provides improved performance for all face center strikes in comparison to a golf club head that is similar to the golf club head  5400  but filled with another filler material such as a TPE material (e.g., the golf club head  5591 ) or an epoxy material (e.g., the golf club head  5592 ). 
     Tables 17-22 show experimental performance results for three examples of a pitching wedge (PW) golf club having a golf club head constructed according to apparatus, methods, and articles of manufacture described herein for the golf club head  5400  with each example having different filler materials. The golf club head  5691  (not shown) of example 7 was similar to the golf club head  5400  in a PW configuration except that the golf club head  5691  was filled with a thermoplastic elastomer (TPE) filler material with the same or similar properties as any of the TPE materials described herein or in any of the incorporated by reference applications. The golf club head  5692  (not shown) of example 8 was similar to the golf club head  5400  in a PW configuration except that the golf club head  5692  was filled with an epoxy material with the same or similar properties as any of the epoxy materials described herein or in any of the incorporated by reference applications. The golf club head  5693  of example 9 was similar to the golf club head  5400  in a PW configuration and was filled with the first filler material  5712  and the second filler material  5714  as described in detail herein. Accordingly, all three example golf club heads  5691 ,  5692 , and  5693  were structurally similar except for the differences in their filler materials. 
     
       
         
           
               
             
               
                 TABLE 17 
               
             
            
               
                   
               
               
                 Pitching Wedge Golf Club COR at Face Center Location 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Inbound 
                 Outbound 
                 Rebound 
                   
               
               
                   
                 Golf Club 
                 Velocity 
                 Velocity 
                 Time 
               
               
                   
                 Head 
                 (mph) 
                 (mph) 
                 (ms) 
                 COR 
               
               
                   
                   
               
               
                   
                 Golf Club 
                 124.72 
                 66.65 
                 23.23 
                 0.776 
               
               
                   
                 Head 5691 
               
               
                   
                 Golf Club 
                 124.92 
                 68.52 
                 22.83 
                 0.792 
               
               
                   
                 Head 5692 
               
               
                   
                 Golf Club 
                 124.78 
                 68.53 
                 22.84 
                 0.793 
               
               
                   
                 Head 5693 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 18 
               
             
            
               
                   
               
               
                 Pitching Wedge Golf Club Ball Speed 
               
               
                 (mph) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 91.15 
                 90.22 
                 89.78 
                 90.48 
                 87.82 
               
               
                 5691 
               
               
                 Golf Club Head 
                 92.05 
                 91.00 
                 90.12 
                 91.50 
                 88.17 
               
               
                 5692 
               
               
                 Golf Club Head 
                 92.30 
                 91.15 
                 90.25 
                 91.33 
                 88.38 
               
               
                 5693 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 19 
               
             
            
               
                   
               
               
                 Pitching Wedge Golf Club Launch Angle 
               
               
                 (radians) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 25.88 
                 25.40 
                 26.22 
                 26.58 
                 24.47 
               
               
                 5691 
               
               
                 Golf Club Head 
                 26.32 
                 25.57 
                 26.25 
                 26.48 
                 24.45 
               
               
                 5692 
               
               
                 Golf Club Head 
                 26.70 
                 25.55 
                 26.43 
                 26.88 
                 24.85 
               
               
                 5693 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 20 
               
             
            
               
                   
               
               
                 Pitching Wedge Golf Club Backspin 
               
               
                 (rpm) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 8527 
                 8757 
                 8083 
                 8173 
                 9100 
               
               
                 5691 
               
               
                 Golf Club Head 
                 8372 
                 8735 
                 8011 
                 8432 
                 8931 
               
               
                 5692 
               
               
                 Golf Club Head 
                 8201 
                 8806 
                 8101 
                 8301 
                 8982 
               
               
                 5693 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 21 
               
             
            
               
                   
               
               
                 Pitching Wedge Golf Club Peak Height 
               
               
                 (yards) vs. Face Portion Location 
               
            
           
           
               
               
               
            
               
                   
                 Face Location 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 26.83 
                 25.50 
                 26.00 
                 27.00 
                 23.00 
               
               
                 5691 
               
               
                 Golf Club Head 
                 27.67 
                 26.17 
                 26.17 
                 27.17 
                 23.17 
               
               
                 5692 
               
               
                 Golf Club Head 
                 28.17 
                 26.17 
                 26.50 
                 27.83 
                 24.00 
               
               
                 5693 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 22 
               
             
            
               
                   
               
               
                 Pitching Wedge Golf Club Carry Distance 
               
               
                 (yards) vs. Face Portion Location 
               
            
           
           
               
               
            
               
                   
                 Face Location 
               
            
           
           
               
               
               
               
               
               
            
               
                 Golf Club Head 
                 Center 
                 Toe 
                 Heel 
                 High 
                 Low 
               
               
                   
               
               
                 Golf Club Head 
                 122.50 
                 120.50 
                 120.67 
                 121.67 
                 116.67 
               
               
                 5691 
               
               
                 Golf Club Head 
                 123.83 
                 121.83 
                 121.67 
                 122.67 
                 117.67 
               
               
                 5692 
               
               
                 Golf Club Head 
                 124.17 
                 122.00 
                 121.50 
                 122.50 
                 117.50 
               
               
                 5693 
               
               
                   
               
            
           
         
       
     
     Referring to Table 17, the golf club head  5693  has a higher COR for face center strikes than the golf club heads  5691  and  5692 . Accordingly, as shown in Table 18, the golf club head  5693  provides a higher ball speed than golf club heads  5691  and  5692  at the center location. In particular, at the center location, the increase in ball speed for the golf club head  5693  relative to the golf club head  5691  is over one (1) mph, and the increase in ball speed for the golf club head  5693  relative to the golf club head  5692  is nearly 0.5 mph. With reference to Table 22, the increase in ball speed at the center location of the golf club head  5693  provides a greater total ball carry distance for the golf club head  5693  in comparison to the golf club head  5691  and the golf club head  5692 . In particular, at the center location, the increase in carry distance for the golf club head  5693  relative to the golf club head  5691  is nearly (2) yards, and the increase in carry distance for the golf club head  5693  relative to the golf club head  5692  is nearly 0.5 yards. As described herein, the center location of the face portion may represent the highest statistical strike region on the face portion. In other words, many individuals may strike a golf ball at or proximate to the center location. Accordingly, the golf club head  5693  as described in detail herein (e.g., filled with the first and second filler materials  5712  and  5714 , respectively) provides improved performance for all face center strikes in comparison to a golf club head that is similar to the golf club head  5400  but filled with another filler material such as a TPE material (e.g., the golf club head  5691 ) or an epoxy material (e.g., the golf club head  5692 ). Further, the ball speed and carry distance for the golf club head  5693  at the heel, the toe, the high, and the low face locations are greater than the ball speed and carry distance for the same locations, respectively, for the golf club heads  5691  and  5692 . Accordingly, the golf club head  5693  as described in detail herein (e.g., filled with the first and second filler materials  5712  and  5714 , respectively) provides an overall improved performance for all face locations of the golf club head  5693  in comparison to a golf club head that is similar to the golf club head  5400  but filled with another filler material such as a TPE material (e.g., the golf club head  5691 ) or an epoxy material (e.g., the golf club head  5692 ). 
     In one example, the deflections of the center locations of the face portions  5462  of the golf club head  5592  and  5593  in response to golf ball strikes where numerically determined using finite element analysis (FEA). The numerically modeled collision was between a two-part golf ball (USGA Bridgestone Calibration Ball) traveling at 38 m/s (85 mph) and each of the golf club heads  5592  and  5593  in a fixed position with each of the golf club heads  5592  and  5592  having a face portion thickness of approximately 0.059 inches (1.5 mm). The results of the FEA are shown in Table 23 considering nearly identical force at maximum face portion deflection (i.e., nearly identical deformed shapes for the golf ball). 
     
       
         
           
               
               
               
               
             
               
                 TABLE 23 
               
               
                   
               
               
                   
                 Time at Maximum 
                 Time at Face 
                 Maximum Face 
               
               
                 Golf Club 
                 Face Center 
                 Portion 
                 Center 
               
               
                 Head 
                 Displacement (s) 
                 Rebound (s) 
                 Displacement (mm) 
               
               
                   
               
             
            
               
                 Golf Club 
                 2.03E−04 
                 5.82E−04 
                 0.36 
               
               
                 Head 5592 
               
               
                 Golf Club 
                 2.74E−04 
                 5.88E−04 
                 0.70 
               
               
                 Head 5593 
               
               
                   
               
            
           
         
       
     
     As shown in Table 23, the time to reach maximum face center deflection measured from the time the golf ball collides with the face portion  5462  and the rebound time for the face portion  5462  (i.e., time to reach near zero deflection from maximum deflection) are nearly the same for both golf club heads  5592  and  5593 . However, as shown in Table 23, the maximum deflection of the face portion  5462  for the golf club head  5593  is nearly twice as large as the maximum deflection of the face portion  5462  for the golf club head  5593  for the nearly the same maximum deflection and rebound time interval. Accordingly, the relatively large deflection and subsequent rebound of the face portion  5462  of the golf club head  5593  in the same time interval as the golf club head  5592  (i.e., higher face rebound velocity) may provide a larger transfer of rebound energy to the golf ball to result in the increased golf ball velocities and carry distances described herein to the golf club head  5593 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS.  93  and  94   , a golf club head  9300  may include a body portion  9310  having a toe portion (not shown in  FIGS.  93  and  94   ), a heel portion (not shown in  FIGS.  93  and  94   ), a front portion  9360  with a face portion  9362  (e.g., a strike face) having a front surface  9364  and a back surface  9366 , a back portion  9370  having a back wall portion  9372 , a top portion  9380 , and a sole portion  9390 . The face portion  9362  may be an integral portion of the body portion  9310 . Alternatively, the face portion  9362  may be a separate piece or an insert coupled to the body portion  9310  via various manufacturing methods and/or processes described herein. The golf club head  9300  may be similar in many respects to any of the golf club heads described herein. Accordingly, the golf club head  9300  may include an interior cavity  9375 , one or a plurality of ports (not shown in  FIGS.  93  and  94   ), and/or one or a plurality of mass portions (not shown in  FIGS.  93  and  94   ) similar to any of the golf club heads described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The interior cavity  9375  may be partially or entirely filled with one or more filler materials (i.e., a cavity filling material), which may include one or more similar or different types of materials. In one example, as shown in  FIGS.  93  and  94   , the interior cavity  9375  may be partially filled with a filler material  9412 , which may be similar to any of the filler materials described herein. In one example, the filler material  9412  may be a TPE material similar to any of the TPE materials described herein. In another example, the filler material  9412  may be a thermoset material similar to any of the thermoset materials described herein such as an epoxy-based material. In yet another example, the filler material  9412  may be a rubber-based compound such as any of the rubber-based compounds described herein. The filler material  9412  may be coupled or attached to the back surface  9366  of the face portion  9362  similar to the coupling of a filler material to the back surface of the face portion of any of the golf club heads described herein. The material, size, shape, configuration, location in the interior cavity  9375 , coupling to the face portion  9362 , and/or any other property or configuration of the filler material  9412  may be similar to the same property or configuration of the filler material of any of the golf club head described herein. In another example (not shown), any remaining unfilled portion of the interior cavity  9375  may also be filled with another filler material having different physical properties than the filler material  9412 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As shown in  FIGS.  93  and  94   , the golf club head  9300  may include an internal mass portion  9420  coupled to a back surface of the filler material  9412 . In one example, the internal mass portion  9420  may be located and/or centered at or proximate to the ball strike region of the golf club head  9300  and be sufficiently large to encompass all or substantial portions of the ball strike region of the golf club head  9300 . In other words, a portion of the filler material  9412  behind the ball strike region of the face portion  9362  may be sandwiched by the ball strike region of the face portion  9362  and the internal mass portion  9420 . In another example, the internal mass portion  9420  may be located and/or centered at or proximate to the geometric center of the face portion  9362 . In yet another example, the internal mass portion  9420  may be located and/or centered at or proximate to the center of gravity of the golf club head  9300 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  93   , a gap  9424  may be defined as a distance between the inner surface  9378  of the body portion  9310  that defines the interior cavity  9375  and the internal mass portion  9420 . In the example of  FIG.  93   , the gap  9424  is shown to be between the internal mass portion  9420  and the back wall portion  9372 . As shown in  FIG.  93   , the internal mass portion  9420  may be spaced apart from all portions of the inner surface  9378  (i.e., the inner walls). In other words, the internal mass portion  9420  may not contact any portion of the inner surface  9378  of the body portion  9310  that defines the interior cavity  9375 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The internal mass portion  9420  may be attached to the filler material  9412  via various manufacturing methods and/or processes. In one example, the internal mass portion  9420  may be bonded or attached to the filler material  9412  with an adhesive. In another example (not shown), the internal mass portion  9420  may be maintained in position against the filler material  9412  as described herein by another filler material (not shown) in the gap  9424 . In another example, as shown in  FIGS.  93  and  94   , the filler material  9412  may include a correspondingly shaped depression or recess to receive all of portions of the internal mass portion  9420 . In yet another example, the filler material  9412  may surround portions of the internal mass portion  9420 . As described herein, the internal mass portion  9420  may be attached to the filler material  9412  and yet be spaced apart from all portions of the inner surface  9378  (i.e., the inner walls) of the body portion  9310  that defines the interior cavity  9375 . Accordingly, the internal mass portion  9420  may be moveable in the interior cavity  9375  and relative to the body portion  9310  and the face portion  9362  to the extent allowed by the compression and expansion of the filler material  9412  as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The internal mass portion  9420  may have any shape, size and/or thickness. The internal mass portion  9420  may be constructed from a material with a relatively higher density than the filler material  9412 . For example, the internal mass portion  9420  may be constructed from metal or metal alloys based on steel, titanium, magnesium, tungsten, and/or other metals. The internal mass portion  9420  may be constructed from a material with a relatively higher density than the material of the body portion  9310 . In one example, the internal mass portion  9420  may be constructed from a tungsten-based material, whereas the body portion  9310  may be constructed from a steel-based material. As shown in the example of  FIGS.  93  and  94   , the internal mass portion  9420  may be disc shaped. In one example, the internal mass portion  9420  may have a similar diameter as the diameter of a golf ball (not shown). In another example, the internal mass portion  9420  may have a diameter that is larger than the diameter of a golf ball. In another example, the internal mass portion  9420  may have a diameter corresponding to all or substantial portions of the ball strike region of the face portion  9362 . In yet another example, the internal mass portion may have rectangular shape. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIG.  93   , the thickness of the internal mass portion  9420  may be less than the thickness of the filler material  9412 . In another example, the thickness of the internal mass portion  9420  may be greater than or equal to the thickness of the filler material  9412 . In another example, the combined thickness of the internal mass portion  9420  and the filler material  9412  may be similar to the width of the gap  9424  at the widest region of the interior cavity  9375  (i.e., the greatest width of the interior cavity  9375  between the face portion  9362  and the back wall portion  9372 . In another example, the combined thickness of the internal mass portion  9420  and the filler material  9412  may be less than the width of the gap  9424  at the widest region of the interior cavity  9375 . In another example, the combined thickness of the internal mass portion  9420  and the filler material  9412  may be greater than the width of the gap  9424  at the widest region of the interior cavity  9375 . In another example, the thickness of the filler material  9412  may be greater than width of the gap  9424  at the widest region of the interior cavity  9375 . In yet another example, the thickness of the internal mass portion  9420  may greater than the width of the gap  9424  at the widest region of the interior cavity  9375 . The thickness of the filler material  9412 , the thickness and configuration of the internal mass portion  9420 , and the width of the gap  9424  may be determined according to the loft angle of the golf club head  9300  to optimize CG location, increase or optimize MOI, and provide better sound and feel for the golf club head  9300 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The internal mass portion  9420  may be attached to the filler material  9412 . Accordingly, the internal mass portion  9420  may move in the interior cavity  9375  to the extent allowed by the elasticity of the filler material  9412 . In other words, the internal mass portion  9420  may be moveable toward the face portion  9362  by compression of the filler material  9412 , and conversely, movable away from the face portion  9362  by expansion of the filler material  9412 . The internal mass portion  9420  may move with the same acceleration and speed as the golf club head  9300  in response to the swinging motion of the golf club head  9300 . Accordingly, as the face portion  9362  impacts a golf ball (not shown), the face portion  9362  may deflect inward to compress the filler material  9412  as described herein. The forward momentum of the internal mass portion  9420  may further compress the filler material  9412  to enhance or increase the elastic rebounding effect of the filler material  9412 . Accordingly, the velocity of the golf ball may increase, which may increase ball distance. In other words, a portion of the kinetic energy of the internal mass portion  9420  due to the swinging motion of the golf club head  9300  may be transferred to the filler material  9412  as potential energy (i.e., compression of the filler material  9412 ) in response to the face portion  9362  striking the golf ball. The potential energy stored in the filler material  9412  imparted from the internal mass portion  9420  may then be transferred as kinetic energy to the golf ball. Further, a portion of the kinetic energy of the internal mass portion  9420  that may not be utilized for compressing the filler material  9412  may be directly transferred to the golf ball via the filler material  9412  and the face portion  9362 . Accordingly, the golf ball may attain a higher speed, which in turn, may result in a longer golf ball travel distance. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion and/or the face portion of any of the golf club heads described herein may be partially or entirely made of a steel-based material (e.g., 17-4 PH stainless steel, Nitronic® 50 stainless steel, alloy steel 8620, maraging steel or other types of stainless steel), a titanium-based material, an aluminum-based material (e.g., a high-strength aluminum alloy or a composite aluminum alloy coated with a high-strength alloy), any combination thereof, non-metallic materials, composite materials, and/or other suitable types of materials. The body portion and/or the face portion may be constructed with materials that are similar to any of the body portions and/or face portions described herein or in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the area of the front surface of the face portion of any of the golf club heads described herein may be greater than or equal to 330 mm 2  and less than or equal to 5000 mm 2 . In another example, the area of the front surface of the face portion of any of the golf club heads described herein may be greater than or equal to 1000 mm 2  and less than or equal to 5300 mm 2 . In yet another example, the area of the front surface of the face portion of any of the golf club heads described herein may be greater than or equal to 1500 mm 2  and less than or equal to 4800 mm 2 . While the above examples may describe particular areas, the area of the front surface may greater than or less than those numbers. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, a filler material may include an elastic polymer or an elastomer material (e.g., a viscoelastic urethane polymer material such as Sorbothane® material manufactured by Sorbothane, Inc., Kent, Ohio), a thermoplastic elastomer material (TPE), a thermoplastic polyurethane material (TPU), other polymer material(s), bonding material(s) (e.g., adhesive), and/or other suitable types of materials that may absorb shock, isolate vibration, and/or dampen noise. In another example, a filler material may be one or more thermoset polymers having bonding properties (e.g., one or more adhesive or epoxy materials). A material may also absorb shock, isolate vibration, and/or dampen noise when a golf club head as described herein strikes a golf ball. Further, a filler material may be an epoxy material that may be flexible or slightly flexible when cured. In another example, a filler material may include any of the 3M™ Scotch-Weld™ DP100 family of epoxy adhesives (e.g., 3M™ Scotch-Weld™ Epoxy Adhesives DP100, DP100 Plus, DP100NS and DP100FR), which are manufactured by 3M corporation of St. Paul, Minn. In another example, a filler material may include 3M™ Scotch-Weld™ DP100 Plus Clear adhesive. In another example, a filler material may include low-viscosity, organic, solvent-based solutions and/or dispersions of polymers and other reactive chemicals such as MEGUM™, ROBOND™, and/or THIXON™ materials manufactured by the Dow Chemical Company, Auburn Hills, Mich. In yet another example, a filler material may be LOCTITE® materials manufactured by Henkel Corporation, Rocky Hill, Conn. In another example, a filler material may be a polymer material such as an ethylene copolymer material that may absorb shock, isolate vibration, and/or dampen noise when a golf club head strikes a golf ball via the face portion. In another example, a filler material may be a high density ethylene copolymer ionomer, a fatty acid modified ethylene copolymer ionomer, a highly amorphous ethylene copolymer ionomer, an ionomer of ethylene acid acrylate terpolymer, an ethylene copolymer comprising a magnesium ionomer, an injection moldable ethylene copolymer that may be used in conventional injection molding equipment to create various shapes, an ethylene copolymer that can be used in conventional extrusion equipment to create various shapes, an ethylene copolymer having high compression and low resilience similar to thermoset polybutadiene rubbers, and/or a blend of highly neutralized polymer compositions, highly neutralized acid polymers or highly neutralized acid polymer compositions, and fillers. For example, the ethylene copolymer may include any of the ethylene copolymers associated with DuPont™ High-Performance Resin (HPF) family of materials (e.g., DuPont™ HPF AD1172, DuPont™ HPF AD1035, DuPont® HPF 1000 and DuPont™ HPF 2000), which are manufactured by E.I. du Pont de Nemours and Company of Wilmington, Del. The DuPont™ HPF family of ethylene copolymers are injection moldable and may be used with conventional injection molding equipment and molds, provide low compression, and provide high resilience, i.e., relatively high coefficient of restitution (COR). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. A filler material not specifically described in detail herein may include one or more similar or different types of materials described herein and in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Any of the filler materials described herein may be subjected to different processes during manufacturing of any of the golf club heads described herein. Such processes may include one or more filler materials being heated and/or cooled by conduction, convection, and/or radiation during one or more injection molding processes or post injection molding curing processes. For example, all of the heating and cooling processes may be performed by using heating or cooling systems that employ conveyor belts that move a golf club head described herein through a heating or cooling environment for a period of time as described herein. The processes of manufacturing a golf club head with one or more filler materials may be similar to any of the processes described in any of the incorporated by reference applications. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Any of the golf club heads described herein may be manufactured by casting from metal such as steel. However, other techniques for manufacturing a golf club head as described herein may be used such as 3D printing, or molding a golf club head from metal or non-metal materials such as ceramics. 
     All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Although a particular order of actions may be described herein with respect to one or more processes, these actions may be performed in other temporal sequences. Further, two or more actions in any of the processes described herein may be performed sequentially, concurrently, or simultaneously. 
     Procedures defined by golf standard organizations and/or governing bodies such as the United States Golf Association (USGA) and/or the Royal and Ancient Golf Club of St. Andrews (R&amp;A) may be used for measuring the club head volume of any of the golf club heads described herein. For example, a club head volume may be determined by using the weighted water displacement method (i.e., Archimedes Principle). Although the figures may depict particular types of club heads (e.g., a driver-type club head or iron-type golf club head), the apparatus, methods, and articles of manufacture described herein may be applicable to other types of club head (e.g., a fairway wood-type club head, a hybrid-type club head, a putter-type club head, etc.). Accordingly, any golf club head as described herein may have a volume that is within a volume range corresponding to certain type of golf club head as defined by golf governing bodies. A driver-type golf club head may have a club head volume of greater than or equal to 300 cubic centimeters (cm3 or cc). In another example, a driver-type golf club head may have a club head volume of 460 cc. A fairway wood golf club head may have a club head volume of between 100 cc and 300 cc. In one example, a fairway wood golf club head may have a club head volume of 180 cc. An iron-type golf club head may have a club head volume of between 25 cc and 100 cc. In one example, an iron-type golf club head may have a volume of 50 cc. Any of the golf clubs described herein may have the physical characteristics of a certain type of golf club (i.e., driver, fairway wood, iron, etc.), but have a volume that may fall outside of the above described ranges. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As the rules of golf may change from time to time (e.g., new regulations may be adopted or old rules may be eliminated or modified by golf standard organizations and/or governing bodies such as the United States Golf Association (USGA), the Royal and Ancient Golf Club of St. Andrews (R&amp;A), etc.), golf equipment related to the apparatus, methods, and articles of manufacture described herein may be conforming or non-conforming to the rules of golf at any particular time. Accordingly, golf equipment related to the apparatus, methods, and articles of manufacture described herein may be advertised, offered for sale, and/or sold as conforming or non-conforming golf equipment. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     While the above examples may describe an iron-type or a wedge-type golf club head, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of golf club heads (e.g., a driver-type golf club head, a fairway wood-type golf club head, a hybrid-type golf club head, a putter-type golf club head, etc.). Further, although the above examples may describe steel-based material, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of metal materials, non-metal materials, or both. 
     Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. A numerical range defined using the word “between” includes numerical values at both end points of the numerical range. A spatial range defined using the word “between” includes any point within the spatial range and the boundaries of the spatial range. A location expressed relative to two spaced apart or overlapping elements using the word “between” includes (i) any space between the elements, (ii) a portion of each element, and/or (iii) the boundaries of each element. 
     The terms “a,” “an,” and/or “the” used in the context of describing various embodiments the present disclosure are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The term “coupled” and any variation thereof refer to directly or indirectly connecting two or more elements chemically, mechanically, and/or otherwise. The phrase “removably connected” is defined such that two elements that are “removably connected” may be separated from each other without breaking or destroying the utility of either element. 
     The term “substantially” when used to describe a characteristic, parameter, property, or value of an element may represent deviations or variations that do not diminish the characteristic, parameter, property, or value that the element may be intended to provide. Deviations or variations in a characteristic, parameter, property, or value of an element may be based on, for example, tolerances, measurement errors, measurement accuracy limitations and other factors. The term “proximate” is synonymous with terms such as “adjacent,” “close,” “immediate,” “nearby”, “neighboring”, etc., and such terms may be used interchangeably as appearing in this disclosure. 
     The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely for clarification and does not pose a limitation on the scope of the present disclosure. No language in the specification should be construed as indicating any non-claimed element essential to the practice of any embodiments discussed herein. The apparatus, methods, and articles of manufacture described herein may be implemented in a variety of embodiments, and the foregoing description of some of these embodiments does not necessarily represent a complete description of all possible embodiments. Instead, the description of the drawings, and the drawings themselves, disclose at least one embodiment, and may disclosure alternative embodiments. 
     Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements disclosed herein. One or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims. 
     While different features or aspects of an embodiment may be described with respect to one or more features, a singular feature may comprise multiple elements, and multiple features may be combined into one element without departing from the scope of the present disclosure. Further, although methods may be disclosed as comprising one or more operations, a single operation may comprise multiple steps, and multiple operations may be combined into one step without departing from the scope of the present disclosure. 
     Although certain example apparatus, methods, and articles of manufacture have been described herein, the scope of coverage of this disclosure is not limited thereto. On the contrary, this disclosure covers all apparatus, methods, and articles of articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.