Patent Publication Number: US-2018050244-A1

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

Description:
CROSS REFERENCE 
     This application is a continuation of U.S. patent application Ser. No. 15/785,001, filed Oct. 16, 2017. This application also claims the benefit of U.S. Provisional Application Ser. No. 62/502,442, filed May 5, 2017, U.S. Provisional Application Ser. No. 62/508,794, filed May 19, 2017, U.S. Provisional Application Ser. No. 62/512,033, filed May 28, 2017, and U.S. Provisional Application Ser. No. 62/570,493, filed Oct. 10, 2017. This application is a continuation-in-part of U.S. Non-Provisional application Ser. No. 15/687,317, filed Aug. 25, 2017, which is a continuation of U.S. Non-Provisional application Ser. No. 15/433,753, filed Feb. 15, 2017, now U.S. Pat. No. 9,764,208, which claims the benefit of U.S. Provisional Application No. 62/343,739, filed May 31, 2016. U.S. Non-Provisional application Ser. No. 15/433,753, now U.S. Pat. No. 9,764,208, is also a continuation application of U.S. Non-Provisional application Ser. No. 15/188,718, filed Jun. 21, 2016, now U.S. Pat. No. 9,610,481, which claims the benefit of U.S. Provisional Application No. 62/343,739, filed May 31, 2016. This application is also a continuation-in-part of U.S. Non-Provisional application Ser. No. 15/701,131, filed Sep. 11, 2017, which is a continuation of U.S. Non-provisional application Ser. No. 15/685,986, filed Aug. 24, 2017, which is a continuation of U.S. patent application Ser. No. 15/628,251, filed Jun. 20, 2017, which is a continuation of U.S. Non-Provisional application Ser. No. 15/209,364, filed on Jul. 13, 2016, which is a continuation application of U.S. Non-Provisional application Ser. No. 14/589,277, filed Jan. 5, 2015, now U.S. Pat. No. 9,421,437, which is a continuation application of U.S. Non-Provisional application Ser. No. 14/513,073, filed Oct. 13, 2014, now U.S. Pat. No. 8,961,336, which is a continuation application of U.S. Non-Provisional application Ser. No. 14/498,603, filed Sep. 26, 2014, now U.S. Pat. No. 9,199,143, which claims the benefit of U.S. Provisional Application No. 62/041,538, filed Aug. 25, 2014. U.S. Non-Provisional application Ser. No. 15/209,364, filed on Jul. 13, 2016 is also a continuation application of U.S. Non-Provisional application Ser. No. 14/618,501, filed Feb. 10, 2015, now U.S. Pat. No. 9,427,634, which is a continuation application of U.S. Non-Provisional application Ser. No. 14/589,277, filed Jan. 5, 2015, now U.S. Pat. No. 9,421,437. U.S. Non-Provisional application Ser. No. 15/209,364, filed on Jul. 13, 2016, is also a continuation application of International Application No. PCT/US15/16666, filed Feb. 19, 2015, which claims the benefits of U.S. Provisional Application No. 61/942,515, filed Feb. 20, 2014, U.S. Provisional Application No. 61/945,560, filed Feb. 27, 2014, U.S. Provisional Application No. 61/948,839, filed Mar. 6, 2014, U.S. Provisional Application No. 61/952,470, filed Mar. 13, 2014, U.S. Provisional Application No. 61/992,555, filed May 13, 2014, U.S. Provisional Application No. 62/010,836, filed Jun. 11, 2014, U.S. Provisional Application No. 62/011,859, filed Jun. 13, 2014, and U.S. Provisional Application No. 62/032,770, filed Aug. 4, 2014. U.S. Non-Provisional application Ser. No. 15/209,364, filed on Jul. 13, 2016 is also a continuation application of International Application No. PCT/US14/71250, filed Dec. 18, 2014, which is a continuation of U.S. Non-Provisional application Ser. No. 14/498,603, filed Sep. 26, 2014, now U.S. Pat. No. 9,199,143. The disclosures of the referenced applications are incorporated herein by reference. 
    
    
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a front view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG. 2  depicts a rear view of the example golf club head of  FIG. 1 . 
         FIG. 3  depicts a top view of the example golf club head of  FIG. 1 . 
         FIG. 4  depicts a bottom view of the example golf club head of  FIG. 1 . 
         FIG. 5  depicts a left view of the example golf club head of  FIG. 1 . 
         FIG. 6  depicts a right view of the example golf club head of  FIG. 1 . 
         FIG. 7  depicts a cross-sectional view of the example golf club head of  FIG. 1  along line  7 - 7 . 
         FIG. 8  depicts a cross-sectional view of the example golf club head of  FIG. 1  along line  8 - 8 . 
         FIG. 9  depicts a cross-sectional view of the example golf club head of  FIG. 1  along line  9 - 9 . 
         FIG. 10  depicts another rear view of the example golf club head of  FIG. 1 . 
         FIG. 11  depicts a top view of a mass portion associated with the example golf club head of  FIG. 1 . 
         FIG. 12  depicts a side view of a mass portion associated with the example golf club head of  FIG. 1 . 
         FIG. 13  depicts a side view of another mass portion associated with the example golf club head of  FIG. 1 . 
         FIG. 14  depicts a rear view of a body portion of the example golf club head of  FIG. 1 . 
         FIG. 15  depicts a cross-sectional view of a face portion of the example golf club head of  FIG. 1 . 
         FIG. 16  depicts a cross-sectional view of another face portion of the example golf club head of  FIG. 1 . 
         FIG. 17  depicts one manner in which the example golf club head described herein may be manufactured. 
         FIG. 18  depicts another cross-sectional view of the example golf club head of  FIG. 4  along line  18 - 18 . 
         FIG. 19  depicts a cross-sectional view of the example golf club head of  FIG. 1 . 
         FIG. 20  depicts another manner in which an example golf club head described herein may be manufactured. 
         FIG. 21  depicts yet another manner in which an example golf club head described herein may be manufactured. 
         FIG. 22  depicts a front view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG. 23  depicts a rear view of the example golf club head of  FIG. 22 . 
         FIG. 24  depicts a front perspective view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG. 25  depicts a rear perspective view of the example golf club head of  FIG. 24 . 
         FIG. 26  depicts another rear perspective view of the example golf club head of  FIG. 24 . 
         FIG. 27  depicts a perspective bottom view of the example golf club head of  FIG. 24 . 
         FIG. 28  depicts a perspective toe-side view of the example golf club head of  FIG. 24 . 
         FIG. 29  depicts a perspective heel-side view of the example golf club head of  FIG. 24 . 
         FIG. 30  depicts a front view of a golf club head according to an embodiment of the apparatus, methods, and articles of manufacture described herein. 
         FIG. 31  depicts a rear view of the example golf club head of  FIG. 30 . 
         FIG. 32  depicts a bottom view of the example golf club head of  FIG. 30 . 
         FIG. 33  depicts a perspective toe-side view of the example golf club head of  FIG. 30 . 
         FIG. 34  depicts a perspective heel-side view of the example golf club head of  FIG. 30 . 
         FIGS. 35 and 36  depict a perspective cross-sectional view of the example golf club head of  FIG. 30  taken at section lines  35 - 35  of  FIG. 37 . 
         FIG. 37  depicts a front perspective view of the example golf club head of  FIG. 30  shown with the face portion removed. 
         FIG. 38  depicts a perspective cross-sectional view of the example golf club head of  FIG. 30  taken at section lines  38 - 38  of  FIG. 37 . 
         FIG. 39  depicts an enlarged view of area  39  of  FIG. 35 . 
         FIG. 40  depicts yet another manner in which an example golf club head described herein may be manufactured. 
         FIG. 41  depicts yet another manner in which an example golf club head described herein may be manufactured. 
         FIG. 42  depicts an example of curing a bonding agent. 
     
    
    
     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 
     In general, golf club heads and methods to manufacture golf club heads are described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In the example of  FIGS. 1-14 , a golf club head  100  may include a body portion  110  ( FIG. 14 ) having a toe portion  140 , a heel portion  150 , a front portion  160  with a face portion  162  (e.g., a strike face) having a front surface  164  and a back surface  166 , a back portion  170 , a top portion  180 , and a sole portion  190 . The toe portion  140 , the heel portion  150 , the front portion  160 , the back portion  170 , the top portion  180 , and/or the sole portion  190  may partially overlap each other. For example, a portion of the toe portion  140  may overlap portion(s) of the front portion  160 , the back portion  170 , the top portion  180 , and/or the sole portion  190 . In a similar manner, a portion of the heel portion  150  may overlap portion(s) of the front portion  160 , the back portion  170 , the top portion  180 , and/or the sole portion  190 . In another example, a portion of the back portion  170  may overlap portion(s) of the toe portion  140 , the heel portion  150 , the top portion  180 , and/or the sole portion  190 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The golf club head  100  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 (0°), 48°, 52°, 56°, 60°, etc.). Although  FIGS. 1-10  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 apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The toe portion  140  may include a portion of the body portion  110  opposite of the heel portion  150 . The heel portion  150  may include a hosel portion  155  configured to receive a shaft (not shown) with a grip (not shown) on one end and the golf club head  100  on the opposite end of the shaft to form a golf club. The front surface  164  of the face portion  162  may include one or more score lines, slots, or grooves  168  extending to and/or between the toe portion  140  and the heel portion  150 . While the figures may depict a particular number of grooves, the apparatus, methods, and articles of manufacture described herein may include more or less grooves. The face portion  162  may be used to impact a golf ball (not shown). The face portion  162  may be an integral portion of the body portion  110 . Alternatively, the face portion  162  may be a separate piece or an insert coupled to the body portion  110  via various manufacturing methods and/or processes (e.g., a bonding process such as adhesive, a welding process such as laser welding, a brazing process, a soldering process, a fusing process, a mechanical locking or connecting method, any combination thereof, or other suitable types of manufacturing methods and/or processes). The face portion  162  may be associated with a loft plane that defines the loft angle of the golf club head  100 . The loft angle may vary based on the type of golf club (e.g., a long iron, a middle iron, a short iron, a wedge, etc.). In one example, the loft angle may be between five degrees and seventy-five degrees. In another example, the loft angle may be between twenty degrees and sixty degrees. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The back portion  170  may include a portion of the body portion  110  opposite of the front portion  160 . In one example, the back portion  170  may be a portion of the body portion  110  behind the back surface  166  of the face portion  162 . As shown in  FIG. 6 , for example, the back portion  170  may be a portion of the body portion  110  behind a plane  171  defined by the back surface  166  of the face portion  162 . In another example, the plane  171  may be parallel to the loft plane of the face portion  162 . As mentioned above, for example, the face portion  162  may be a separate piece or an insert coupled to the body portion  110 . Accordingly, the back portion  170  may include remaining portion(s) of the body portion  110  other than the face portion  162 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Further, the body portion  110  may include one or more ports, which may be exterior ports and/or interior ports (e.g., located inside the body portion  110 ). The interior walls of the body portion  110  may include one or more ports. In one example, the back portion  170  may include one or more ports (e.g., inside an interior cavity, generally shown as  700  in  FIG. 7 ). In another example, the body portion  110  may include one or more ports along a periphery of the body portion  110 . As illustrated in  FIG. 14 , for example, the body portion  110  may include one or more ports on the back portion  170 , generally shown as a first set of ports  1420  (e.g., shown as ports  1421 ,  1422 ,  1423 , and  1424 ) and a second set of ports  1430  (e.g., shown as ports  1431 ,  1432 ,  1433 ,  1434 ,  1435 ,  1436 , and  1437 ). In another example, one or more ports may be on a back wall portion  1410  of the back portion  170 . One or more ports may be associated with a port diameter, which may be defined as the largest distance to and/or between opposing ends or boundaries of a port. For example, a port diameter for a rectangular port (e.g., a slot, slit, or elongated rectangular opening) may refer to a diagonal length of a rectangle. In another example, a port diameter of an elliptical port may refer to the major axis of an ellipse. As shown in  FIG. 14 , for example, each port may have a circular shape with a port diameter equivalent to a diameter of a circle. In one example, the port diameter of the first set of ports  1420  and/or the second set of ports  1430  may be about 0.25 inch (6.35 millimeters). Any two adjacent ports of the first set of ports  1420  may be separated by less than or equal to the port diameter. In a similar manner, any two adjacent ports of the second set of ports  1430  may be separated by less than or equal to the port diameter. Some adjacent ports may be separated by greater than the port diameter. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  110  may include one or more mass portions, which may be integral mass portion(s) or separate mass portion(s) that may be coupled to the body portion  110 . In the illustrated example as shown in  FIG. 2 , the body portion  110  may include a first set of mass portions  120  (e.g., shown as mass portions  121 ,  122 ,  123 , and  124 ) and a second set of mass portions  130  (e.g., shown as mass portions  131 ,  132 ,  133 ,  134 ,  135 ,  136 , and  137 ). 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. For example, the first set of mass portions  120  may be a single mass portion. In a similar manner, the second set of mass portions  130  may be a single mass portion. Further, the first set of mass portions or the second set of mass portions  130  may be a portion of the physical structure of the body portion  110 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  110  may be made of a first material whereas the first set of mass portions  120  and/or the second set of mass portions  130  may be made of a second material. The first and second materials may be similar or different materials. For example, the body portion  110  may be partially or entirely made of a steel-based material (e.g., 17-4 PH stainless steel, Nitronic® 50 stainless steel, 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. In one example, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be partially or entirely made of a high-density material such as a tungsten-based material or other suitable types of materials. In another example, one more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be partially or entirely made of other suitable metal material such as a stainless steel-based material, a titanium-based material, an aluminum-based material, any combination thereof, and/or other suitable types of materials. Further, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be made of different types of materials (e.g., metal core and polymer sleeve surrounding the metal core). The body portion  110 , the first set of mass portions  120 , and/or the second set of mass portions  130  may be partially or entirely made of similar or different non-metal materials (e.g., composite, plastic, polymer, etc.). The apparatus, methods, and articles of manufacture are not limited in this regard. 
     One or more ports may be configured to receive a mass portion having a similar shape as the port. For example, a rectangular port may receive a rectangular mass portion. In another example, an elliptical port may receive an elliptical mass portion. As shown in  FIGS. 10 and 14 , for example, the first and second sets of ports  1420  and  1430 , respectively, may be cylindrical ports configured to receive one or more cylindrical mass portions. In particular, one or more mass portions of the first set  120  (e.g., generally shown as mass portions  121 ,  122 ,  123 , and  124 ) may be disposed in a port located at or proximate to the toe portion  140  and/or the top portion  180 . For example, the mass portion  121  may be partially or entirely disposed in the port  1421 . One or more mass portions of the second set  130  (e.g., generally shown as mass portions  131 ,  132 ,  133 ,  134 ,  135 ,  136 , and  137 ) may be disposed in a port located at or proximate to the toe portion  140  and/or the sole portion  190 . For example, the mass portion  135  may be partially or entirely disposed in the port  1435 . The first set of mass portions  120  and/or the second set of mass portions  130  may be coupled to the body portion  110  with various manufacturing methods and/or processes (e.g., a bonding process, a welding process, a brazing process, a mechanical locking method, any combination thereof, or other suitable manufacturing methods and/or processes). 
     Alternatively, the golf club head  100  may not include (i) the first set of mass portions  120 , (ii) the second set of mass portions  130 , or (iii) both the first and second sets of mass portions  120  and  130 , respectively. In particular, the body portion  110  may not include ports at or proximate to the top portion  180  and/or the sole portion  190 . For example, the mass of the first set of mass portions  120  (e.g., 3 grams) and/or the mass of the second set of mass portions  130  (e.g., 16.8 grams) may be integral part(s) of the body portion  110  instead of separate mass portion(s). In one example, the body portion  110  may include interior and/or exterior integral mass portions at or proximate to the toe portion  140  and/or at or proximate to the heel portion  150 . In another example, a portion of the body portion  110  may include interior and/or exterior integral mass portions extending to and/or between the toe portion  140  and the heel portion  150 . The first and/or second set of mass portions  120  and  130 , respectively, may affect the mass, the center of gravity (CG), the moment of inertia (MOI), or other physical properties of the golf club head  100 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     One or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may have similar or different physical properties (e.g., color, marking, shape, size, density, mass, volume, external surface texture, materials of construction, etc.). Accordingly, the first set of mass portions  120  and/or the second set of mass portions  130  may contribute to the ornamental design of the golf club head  100 . In the illustrated example as shown in  FIG. 11 , one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may have a cylindrical shape (e.g., a circular cross section). Alternatively, one or more mass portions of the first set  120  may have a first shape (e.g., a cylindrical shape) whereas one or more mass portions of the second set  130  may have a second shape (e.g., a cubical shape). In another example, the first set of mass portions  120  may include two or more mass portions with different shapes (e.g., the mass portion  121  may be a first shape whereas the mass portion  122  may be a second shape different from the first shape). Likewise, the second set of mass portions  130  may also include two or more mass portions with different shapes (e.g., the mass portion  131  may be a first shape whereas the mass portion  132  may be a second shape different from the first shape). In another example, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  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 the first set of mass portions  120  and/or the second set of mass portions  130 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Although the above examples may describe mass portions having a particular shape, the apparatus, methods, and articles of manufacture described herein may include mass portions of other suitable shapes (e.g., a portion of or a whole sphere, cube, cone, cylinder, pyramid, cuboidal, prism, frustum, rectangular, elliptical, or other suitable geometric shape). While the above examples and figures may depict multiple mass portions as a set of mass portions, two or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be a single piece of mass portion. In one example, the first set of mass portions  120  may be a single piece of mass portion instead of a series of four separate mass portions. In another example, the second set of mass portions  130  may be a single piece of mass portion instead of a series of seven separate mass portions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Referring to  FIGS. 12 and 13 , for example, the first set of mass portions  120  and/or the second set of mass portions  130  may include threads, generally shown as  1210  and  1310 , respectively, to engage with correspondingly configured threads in the ports to secure in the ports of the back portion  170  (e.g., generally shown as  1420  and  1430  in  FIG. 14 ). 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 the first set of mass portions  120  and/or the second set of mass portions  130  may be a screw. One or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may not be readily removable from the body portion  110  with or without a tool. Alternatively, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  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 the first and second sets of mass portions  120  and  130 , respectively. In another example, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be secured in the ports of the back portion  170  with epoxy or adhesive so that the one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may not be readily removable. In yet another example, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be secured in the ports of the back portion  170  with both epoxy and threads so that the one more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may not be readily removable. In yet another example, one or more mass portions described herein may be press fit in a port. In yet another example, one or more 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 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 be 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 the first set of mass portions  120  and/or the second set of mass portions  130  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. 11-13 , one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may have a diameter  1110  of about 0.25 inch (6.35 millimeters) but one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be different in height. In particular, one or more mass portions of the first set of mass portions  120  may be associated with a first height  1220  ( FIG. 12 ), and one or more mass portions of the second set of mass portions  130  may be associated with a second height  1320  ( FIG. 13 ). The first height  1220  may be relatively shorter than the second height  1320 . In one example, the first height  1220  may be about 0.125 inch (3.175 millimeters) whereas the second height  1320  may be about 0.3 inch (7.62 millimeters). In another example, the first height  1220  may be about 0.16 inch (4.064 millimeters) whereas the second height  1320  may be about 0.4 inch (10.16 millimeters). Alternatively, the first height  1220  may be equal to or greater than the second height  1320 . Although the above examples may describe particular dimensions, one or more mass portions described herein may have different dimensions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Referring to  FIG. 10 , for example, the golf club head  100  may be associated with a ground plane  1010 , a horizontal midplane  1020 , and a top plane  1030 . In particular, the ground plane  1010  may be a tangential plane to the sole portion  190  of the golf club head  100  when the golf club head  100  is at an address position (e.g., the golf club head  100  is aligned to strike a golf ball). A top plane  1030  may be a tangential plane to the top portion of the  180  of the golf club head  100  when the golf club head  100  is at the address position. The ground and top planes  1010  and  1030 , respectively, may be substantially parallel to each other. The horizontal midplane  1020  may be vertically halfway between the ground and top planes  1010  and  1030 , respectively. 
     The body portion  110  may include any number of ports (e.g., no ports, one port, two ports, etc.) above the horizontal midplane  1020  and/or below the horizontal midplane  1020 . In one example, the body portion  110  may include a greater number of ports below the horizontal midplane  1020  than above the horizontal midplane  1020 . In the illustrated example as shown in  FIG. 14 , the body portion  110  may include four ports (e.g., generally shown as ports  1421 ,  1422 ,  1423 , and  1424 ) above the horizontal midplane  1020  and seven ports (e.g., generally shown as ports  1431 ,  1432 ,  1433 ,  1434 ,  1435 ,  1436 , and  1437 ) below the horizontal midplane  1020 . In another example (not shown), the body portion  110  may include two ports above the horizontal midplane  1020  and five ports below the horizontal midplane  1020 . In yet another example (not shown), the body portion  110  may not have any ports above the horizontal midplane  1020  but have one or more ports below the horizontal midplane  1020 . Accordingly, the body portion  110  may have more ports below the horizontal midplane  1020  than above the horizontal midplane  1020 . Further, the body portion  110  may include a port at or proximate to the horizontal midplane  1020  with a portion of the port above the horizontal midplane  1020  and a portion of the port below the horizontal midplane  1020 . Accordingly, the port may be (i) above the horizontal midplane  1020 , (ii) below the horizontal midplane  1020 , or (iii) both above and below the horizontal midplane  1020 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     To provide optimal perimeter weighting for the golf club head  100 , the first set of mass portions  120  (e.g., generally shown as mass portions  121 ,  122 ,  123 , and  124 ) may be configured to counter-balance the mass of the hosel  155 . For example, as shown in  FIG. 10 , the first set of mass portions  120  (e.g., generally shown as mass portions  121 ,  122 ,  123  and  124 ) may be located at or near the periphery of the body portion  110  and extend to and/or between the top portion  180  and the toe portion  140 . In other words, the first set of mass portions  120  may be located on the golf club head  100  at a generally opposite location relative to the hosel  155 . In another example, at least a portion of the first set of mass portions  120  may extend at or near the periphery of the body portion  110  and extend along a portion of the top portion  180 . In yet another example, at least a portion of the first set of mass portions  120  may extend at or near the periphery of the body portion  110  and extend along a portion of the toe portion  140 . Further, the first set of mass portions  120  may be above the horizontal midplane  1020  of the golf club head  100 . For example, the first set of mass portions  120  may be at or near the horizontal midplane  1020 . In another example, a portion of the first set of mass portions  120  may be at or above the horizontal midplane  1020  and another portion of the first set of mass portions  120  may be at or below the horizontal midplane  1020 . Accordingly, a set of mass portions, which may be a single mass portion, may have portions above the horizontal midplane  1020  and below the horizontal midplane  1020 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     At least a portion of the first set of mass portions  120  may be at or near the toe portion  140  to increase the MOI of the golf club head  100  about a vertical axis of the golf club head  100  that extends through the CG of the golf club head  100 . Accordingly, the first set of mass portions  120  may be at or near the periphery of the body portion  110  and extend through the top portion  180  and/or the toe portion  140  to counter-balance the mass of the hosel  155  and/or increase the MOI of the golf club head  100 . The locations of the first set of mass portions  120  (i.e., the locations of the first set of ports  1420 ) and the physical properties and materials of construction of the first set of mass portions  120  may be determined to optimally affect the mass, mass distribution, CG, MOI, structural integrity and/or or other static and/or dynamic characteristics of the golf club head  100 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The second set of mass portions  130  (e.g., generally shown as mass portions  131 ,  132 ,  133 ,  134 ,  135 ,  136 , and  137 ) may be configured to place the CG of the golf club head  100  at an optimal location and optimize the MOI of the golf club head  100 . Referring to  FIG. 10 , all or a substantial portion of the second set of mass portions  130  may be generally at or near the sole portion  190 . For example, the second set of mass portions  130  (e.g., generally shown as mass portions  131 ,  132 ,  133 ,  134 ,  135 ,  136 , and  137 ) may be at or near the periphery of the body portion  110  and extend from the sole portion  190  to the toe portion  140 . As shown in the example of  FIG. 10 , the mass portions  131 ,  132 ,  133 , and  134  may be located at or near the periphery of the body portion  110  and extend along the sole portion  190  to lower the CG of the golf club head  100 . The mass portions  135 ,  136  and  137  may be located at or near the periphery of the body portion  110  and extend to and/or between the sole portion  190  and the toe portion  140  to lower the CG and increase the MOI of the golf club head  100 . For example, the MOI of the golf club head  100  about a vertical axis extending through the CG may increase. To lower the CG of the golf club head  100 , all or a portion of the second set of mass portions  130  may be located closer to the sole portion  190  than to the horizontal midplane  1020 . For example, the mass portions  131 ,  132 ,  133 ,  134 ,  135 , and  136  may be closer to the sole portion  190  than to the horizontal midplane  1020 . The locations of the second set of mass portions  130  (i.e., the locations of the second set of ports  1430 ) and the physical properties and materials of construction of the second set of mass portions  130  may be determined to optimally affect the mass, mass distribution, CG, MOI, structural integrity and/or or other static and/or dynamic characteristics of the golf club head  100 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Turning to  FIGS. 7-9 , for example, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be located away from the back surface  166  of the face portion  162  (e.g., not directly coupled to each other). That is, one or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  and the back surface  166  may be partially or entirely separated by an interior cavity  700  of the body portion  110 . As shown in  FIG. 14 , for example, one or more ports of the first and second sets of ports  1420  and  1430  may include an opening (e.g., generally shown as  720  and  730 ) and a port wall (e.g., generally shown as  725  and  735 ). The port walls  725  and  735  may be integral portions of the back wall portion  1410  (e.g., a section of the back wall portion  1410 ) or the body portion  110  depending on the location of each port. The opening  720  may be configured to receive a mass portion such as mass portion  121 . The opening  730  may be configured to receive a mass portion such as mass portion  135 . The opening  720  may be located at one end of the port  1421 , and the port wall  725  may be located or proximate to at an opposite end of the port  1421 . In a similar manner, the opening  730  may be located at one end of the port  1435 , and the port wall  735  may be located at or proximate to an opposite end of the port  1435 . The port walls  725  and  735  may be separated from the face portion  162  (e.g., separated by the interior cavity  700 ). The port wall  725  may have a distance  726  from the back surface  166  of the face portion  162  as shown in  FIG. 9 . The port wall  735  may have a distance  736  from the back surface  166  of the face portion  162 . The distances  726  and  736  may be determined to optimize the location of the CG of the golf club head  100  when the first and second sets of ports  1420  and  1430 , respectively, receive mass portions as described herein. According to one example, the distance  736  may be greater than the distance  726  so that the CG of the golf club head  100  may be moved toward the back portion  170 . As a result, a width  740  of a portion of the interior cavity  700  below the horizontal midplane  1020  may be greater than a width  742  of the interior cavity  700  above the horizontal midplane  1020 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described herein, the CG of the golf club head  100  may be relatively farther back away from the face portion  162  and relatively lower towards a ground plane (e.g., one shown as  1010  in  FIG. 10 ) with all or a substantial portion of the second set of mass portions  130  being at or closer to the sole portion  190  than to the horizontal midplane  1020  and the first and second sets of mass portions  120  and  130 , respectively being away from the back surface  166  than if the second set of mass portions  130  were directly coupled to the back surface  166 . The body portion  110  may include any number of mass portions (e.g., no mass portions, one mass portion, two mass portions, etc.) and/or any configuration of mass portions (e.g., mass portion(s) integral with the body portion  110 ) above the horizontal midplane  1020  and/or below the horizontal midplane  1020 . The locations of the first and second sets of ports  1420  and  1430  and/or the locations (e.g., internal mass portion(s), external mass portion(s), mass portion(s) integral with the body portion  110 , etc.), physical properties and materials of construction of the first set of mass portions  120  and/or the second set of mass portions  130  may be determined to 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  100 . Different from other golf club head designs, the interior cavity  700  of the body portion  110  and the location of the first set of mass portions  120  and/or the second set of mass portion  130  along the periphery of the golf club head  100  may result in a golf ball traveling away from the face portion  162  at a relatively higher ball launch angle and a relatively lower spin rate. As a result, the golf ball may travel farther (i.e., greater total distance, which includes carry and roll distances). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     While the figures may depict ports with a particular cross-section shape, the apparatus, methods, and articles of manufacture described herein may include ports with other suitable cross-section shapes. In one example, the ports of the first and/or second sets of ports  1420  and  1430  may have U-like cross-section shape. In another example, the ports of the first and/or second set of ports  1420  and  1430  may have V-like cross-section shape. One or more of the ports associated with the first set of mass portions  120  may have a different cross-section shape than one or more ports associated with the second set of mass portions  130 . For example, the port  1421  may have a U-like cross-section shape whereas the port  1435  may have a V-like cross-section shape. Further, two or more ports associated with the first set of mass portions  120  may have different cross-section shapes. In a similar manner, two or more ports associated with the second set of mass portions  130  may have different cross-section shapes. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first and second sets of mass portions  120  and  130 , respectively, may be similar in mass (e.g., all of the mass portions of the first and second sets  120  and  130 , respectively, weigh about the same). Alternatively, the first and second sets of mass portions  120  and  130 , respectively, may be different in mass individually or as an entire set. In particular, one or more mass portions of the first set of mass portions  120  (e.g., generally shown as  121 ,  122 ,  123 , and  124 ) may have relatively less mass than one or more portions of the second set of mass portions  130  (e.g., generally shown as  131 ,  132 ,  133 ,  134 ,  135 ,  136 , and  137 ). For example, the second set of mass portions  130  may account for more than 50% of the total mass from mass portions of the golf club head  100 . As a result, the golf club head  100  may be configured to have at least 50% of the total mass from mass portions disposed below the horizontal midplane  1020 . Two or more mass portions in the same set may be different in mass. In one example, the mass portion  121  of the first set  120  may have a relatively lower mass than the mass portion  122  of the first set  120 . In another example, the mass portion  131  of the second set  130  may have a relatively lower mass than the mass portion  135  of the second set  130 . Accordingly, more mass may be distributed away from the CG of the golf club head  100  to increase the MOI about the vertical axis through the CG. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the golf club head  100  may have a mass in the range of about 220 grams to about 330 grams based on the type of golf club (e.g., a 4-iron versus a lob wedge). The body portion  110  may have a mass in the range of about 200 grams to about 310 grams with the first set of mass portions  120  and/or the second set of mass portions  130  having a mass of about 20 grams (e.g., a total mass from mass portions). One or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may have a mass greater than or equal to about 0.1 gram and less than or equal to about 20 grams. In one example, one or more mass portions of the first set  120  may have a mass of about 0.75 gram whereas one or more mass portions of the second set  130  may have a mass of about 2.4 grams. The sum of the mass of the first set of mass portions  120  or the sum of the mass of the second set of mass portions  130  may be greater than or equal to about 0.1 grams and less than or equal to about 20 grams. In one example, the sum of the mass of the first set of mass portions  120  may be about 3 grams whereas the sum of the mass of the first set of mass portions  130  may be about 16.8 grams. The total mass of the second set of mass portions  130  may weigh more than five times as much as the total mass of the first set of mass portions  120  (e.g., a total mass of the second set of mass portions  130  of about 16.8 grams versus a total mass of the first set of mass portions  120  of about 3 grams). The golf club head  100  may have a total mass of 19.8 grams from the first and second sets of mass portions  120  and  130 , respectively (e.g., sum of 3 grams from the first set of mass portions  120  and 16.8 grams from the second set of mass portions  130 ). Accordingly, in one example, the first set of mass portions  120  may account for about 15% of the total mass from mass portions of the golf club head  100  whereas the second set of mass portions  130  may be account for about 85% of the total mass from mass portions of the golf club head  100 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     By coupling the first set of mass portions  120  and/or the second set of mass portions  130 , respectively, to the body portion  110  (e.g., securing the first set of mass portions  120  and/or the second set of mass portions  130  in the ports on the back portion  170 ), the location of the CG and the MOI) of the golf club head  100  may be optimized. In particular, as described herein, the first set of mass portions  120  may lower the location of the CG towards the sole portion  190  and further back away from the face portion  162 . Further, the first set of mass portions  120  and/or the second set of mass portions  130  may increase the MOI as measured about a vertical axis extending through the CG (e.g., perpendicular to the ground plane  1010 ). The MOI may also be higher as measured about a horizontal axis extending through the CG (e.g., extending towards the toe and heel portions  150  and  160 , respectively, of the golf club head  100 ). As a result, the club head  100  may provide a relatively higher launch angle and a relatively lower spin rate than a golf club head without the first and/or second sets of mass portions  120  and  130 , respectively. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Although the figures may depict the mass portions as separate and individual parts that may be visible from an exterior of the golf club head  100 , the two or more mass portions of the first set of mass portions  120  and/or the second set of mass portions  130  may be a single piece of mass portion that may be an exterior mass portion or an interior mass portion (i.e., not visible from an exterior of the golf club head  100 ). In one example, all of the mass portions of the first set  120  (e.g., generally shown as  121 ,  122 ,  123 , and  124 ) may be combined into a single piece of mass portion (e.g., a first mass portion). In a similar manner, all of the mass portions of the second set  130  (e.g., generally shown as  131 ,  132 ,  133 ,  134 ,  135 ,  136 , and  137 ) may be combined into a single piece of mass portion as well (e.g., a second mass portion). In this example, the golf club head  100  may have only two mass portions. In another example (not shown), the body portion  110  may not include the first set of mass portions  120 , but include the second set of mass portions  130  in the form of a single piece of internal mass portion that may be farther from the heel portion  150  than the toe portion  140 . In yet another example (not shown), the body portion  110  may not include the first set of mass portions  120 , but include the second set of mass portions  130  with a first internal mass portion farther from the heel portion  150  than the toe portion  140  and a second internal mass portion farther from the toe portion  140  than the heel portion  150 . The first internal mass portion and the second internal mass portion may be (i) integral parts of the body portion  110  or (ii) separate from the body portion  110  and coupled to the body portion  110 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     While the figures may depict a particular number of mass portions, the apparatus, methods, and articles of manufacture described herein may include more or less number of mass portions. In one example, the first set of mass portions  120  may include two separate mass portions instead of three separate mass portions as shown in the figures. In another example, the second set of mass portions  130  may include five separate mass portions instead of seven separate mass portions as shown in the figures. Alternatively as mentioned above, the apparatus, methods, and articles of manufacture described herein may not include any separate mass portions (e.g., the body portion  110  may be manufactured to include the mass of the separate mass portions as integral part(s) of the body portion  110 ). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Referring to  FIGS. 7-9 , for example, the body portion  110  may be a hollow body including the interior cavity  700  extending between the front portion  160  and the back portion  170 . Further, the interior cavity  700  may extend between the top portion  180  and the sole portion  190 . The interior cavity  700  may be associated with a cavity height  750  (H C ), and the body portion  110  may be associated with a body height  850  (H B ). While the cavity height  750  and the body height  850  may vary between the toe and heel portions  140  and  150 , the cavity height  750  may be at least 50% of a body height  850  (H C &gt;0.5*H B ). For example, the cavity height  750  may vary between 70%-85% of the body height  850 . With the cavity height  750  of the interior cavity  700  being greater than 50% of the body height  850 , the golf club head  100  may produce relatively more consistent feel, sound, and/or result when the golf club head  100  strikes a golf ball via the face portion  162  than a golf club head with a cavity height of less than 50% of the body height. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the interior cavity  700  may be unfilled (i.e., empty space). The body portion  110  with the interior cavity  700  may weigh about 100 grams less than the body portion  110  without the interior cavity  700 . Alternatively, the interior cavity  700  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. In one example, the 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. For example, at least 50% of the interior cavity  700  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  162 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In another example, the filler material may be a polymer material such as an ethylene copolymer material that may absorb shock, isolate vibration, and/or dampen noise when the golf club head  100  strikes a golf ball via the face portion  162 . In particular, at least 50% of the interior cavity  700  may be filled with 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. 
     For example, the filler material may have a density of less than or equal to 1.5 g/cm 3 . The filler material may have a compression deformation value ranging from about 0.0787 inch (2 mm) to about 0.1968 inch (5 mm). The filler material may have a surface Shore D hardness ranging from 40 to 60. As mentioned above, the filler material may have a relatively high coefficient of restitution (COR). The filler material may have a first COR (COR 1 ) and the face portion  2462  may have a second COR (COR 2 ), which may be similar or different from the first COR. The first and second CORs may be associated with a COR ratio (e.g., COR ratio=COR 1 /COR 2  or COR ratio=COR 2 /COR 1 ). In one example, the COR ratio may be less than two (2). In another example, the COR ratio may be in a range from about 0.5 to about 1.5. In yet another example, the COR ratio may be in a range from about 0.8 to about 1.2. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The COR of the filler material may be measured by methods similar to methods that measure the COR of a golf ball as defined by one or more golf standard organizations and/or governing bodies (e.g., United States Golf Association (USGA)). In one example, an air cannon device may launch or eject an approximately 1.55 inch (38.1 mm) spherical sample of the filler material at an initial velocity toward a steel plate positioned at about 4 feet (1.2 meters) away from the air cannon device. The sample may vary in size, shape or any other configuration. A speed monitoring device may be located at a distance in a range from 2 feet (0.6 meters) to 3 feet (0.9 meters) from the air cannon device. The speed monitoring device may measure a rebound velocity of the sample of the filler material after the sample of the filler material strikes the steel plate. The COR may be the rebound velocity divided by the initial velocity. In one example, the filler material may have a COR value in a range from approximately 0.50 to approximately 0.95 when measured with an initial velocity in a range from 100 ft/s (30.48 m/s) to 250 ft/s (76.2 m/s). In another example, the filler material may have a COR value in a range from approximately 0.65 to approximately 0.85 when measured with an initial velocity in a range from 100 ft/s (30.48 m/s) to 150 ft/s (45.72 m/s). In another example, the filler material may have a COR value in a range from approximately 0.75 to approximately 0.8 when measured with an initial velocity in a range 100 ft/s (30.48 m/s) to 150 ft/s (45.72 m/s). In another example, the filler material may have a COR value in a range from approximately 0.55 to approximately 0.90 when measured with an initial velocity in a range from 100 ft/s (30.48 m/s) and 250 ft/s (76.2 m/s). In another example, the filler material may have a COR value in a range from approximately 0.75 to approximately 0.85 when measured with an initial velocity in a range 110 ft/s (33.53 m/s) to 200 ft/s (60.96 m/s). In yet another example, the filler material may have a COR value in a range from approximately 0.8 to approximately 0.9 when measured with an initial velocity of about 125 ft/s (38.1 m/s). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     When the face portion  162  of the golf club head  100  strikes a golf ball, the face portion  162  and the filler material may deform and/or compress. The kinetic energy of the impact may be transferred to the face portion  162  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 filler material may include a bonding portion. In one example, the bonding portion may be one or more bonding agents (e.g., one or more adhesive or epoxy materials). For example, the bonding agent may assist in bonding or adhering the filler material to at least the back surface  166  of the face portion  162 . The bonding agent may also absorb shock, isolate vibration, and/or dampen noise when the golf club head  100  strikes a golf ball via the face portion  162 . Further, the bonding agent may be an epoxy material that may be flexible or slightly flexible when cured. In one example, the 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, the filler material may include 3M™ Scotch-Weld™ DP100 Plus Clear adhesive. In yet another example, the 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, the filler material may be LOCTITE® materials manufactured by Henkel Corporation, Rocky Hill, Conn. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Further, the filler material may include a combination of one or more bonding agents such as any of the bonding agents described herein and one or more polymer materials such as any of the polymer materials described herein. In one example, the filler material may include one or more bonding agents that may be used to bond the polymer material to the back surface  166  of the face portion  162 . The one or more bonding agents may be applied to the back surface  166  of the face portion  162 . The filler material may further include one or more polymer materials may partially or entirely fill the remaining portions of the interior cavity  700 . Accordingly, two or more separate materials may partially or entirely fill the interior cavity  700 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The filler material may only include one or more polymer materials that adhere to inner surface(s) of the interior cavity  700  without a separate bonding agent (e.g., an adhesive or epoxy material). For example, the filler material may include a mixture of one or more polymer materials and one or more bonding agents (e.g., adhesive or epoxy material(s)). Accordingly, the mixture including the one or more polymer materials and the one or more bonding agents may partially or entirely fill the interior cavity  700  and adhere to inner surface(s) of the interior cavity  700 . In another example, the interior cavity  700  may be partially or entirely filled with one or more polymer materials without any bonding agents. In yet another example, the interior cavity  700  may be partially or entirely filled with one or more bonding agents and/or adhesive materials such as an adhesive or epoxy material. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Turning to  FIG. 15 , for example, a thickness of the face portion  162  may be a first thickness  1510  (T 1 ) or a second thickness  1520  (T 2 ). The first thickness  1510  may be a thickness of a section of the face portion  162  adjacent to a groove  168  whereas the second thickness  1520  may be a thickness of a section of the face portion  162  below the groove  168 . For example, the first thickness  1510  may be a maximum distance between the front surface  164  and the back surface  166 . The second thickness  1520  may be based on the groove  168 . In particular, the groove  168  may have a groove depth  1525  (D groove ). The second thickness  1520  may be a maximum distance between the bottom of the groove  168  and the back surface  166 . The sum of the second thickness  1520  and the groove depth  1525  may be substantially equal to the first thickness  1510  (e.g., T 2 +D groove =T 1 ). Accordingly, the second thickness  1520  may be less than the first thickness  1510  (e.g., T 2 &lt;T 1 ). 
     To lower and/or move the CG of the golf club head  100  further back, mass from the front portion  160  of the golf club head  100  may be removed by using a relatively thinner face portion  162 . For example, the first thickness  1510  or the second thickness  1520  may be less than or equal to 0.1 inch (2.54 millimeters). In another example, the first thickness  1510  may be about 0.075 inch (1.905 millimeters) (e.g., T 1 =0.075 inch). With the support of the back wall portion  1410  to form the interior cavity  700  and filling at least a portion of the interior cavity  700  with an elastic polymer material, the face portion  162  may be relatively thinner (e.g., T 1 &lt;0.075 inch) without degrading the structural integrity, sound, and/or feel of the golf club head  100 . In one example, the first thickness  1510  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  1510  may be less than or equal to 0.040 inch (1.016 millimeters) (e.g., T 1 ≦0.040 inch). Based on the type of material(s) used to form the face portion  162  and/or the body portion  110 , the face portion  162  may be even thinner with the first thickness  1510  being less than or equal to 0.030 inch (0.762 millimeters) (e.g., T 1 ≦0.030 inch). The groove depth  1525  may be greater than or equal to the second thickness  1520  (e.g., D groove ≧T 2 ). In one example, the groove depth  1525  may be about 0.020 inch (0.508 millimeters) (e.g., D groove =0.020 inch). Accordingly, the second thickness  1520  may be about 0.010 inch (0.254 millimeters) (e.g., T 2 =0.010 inch). In another example, the groove depth  1525  may be about 0.015 inch (0.381 millimeters), and the second thickness  1520  may be about 0.015 inch (e.g., D groove =T 2 =0.015 inch). Alternatively, the groove depth  1525  may be less than the second thickness  1520  (e.g., D groove &lt;T 2 ). Without the support of the back wall portion  1410  and the elastic polymer material to fill in the interior cavity  700 , a golf club head may not be able to withstand multiple impacts by a golf ball on a face portion. In contrast to the golf club head  100  as described herein, a golf club head with a relatively thin face portion but without the support of the back wall portion  1410  and the elastic polymer material to fill in the interior cavity  700  (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 the golf club head  100 , the face portion  162  may include additional material at or proximate to a periphery of the face portion  162 . Accordingly, the face portion  162  may also include a third thickness  1530 , and a chamfer portion  1540 . The third thickness  1530  may be greater than either the first thickness  1510  or the second thickness  1520  (e.g., T 3 &gt;T 1 &gt;T 2 ). In particular, the face portion  162  may be coupled to the body portion  110  by a welding process. For example, the first thickness  1510  may be about 0.030 inch (0.762 millimeters), the second thickness  1520  may be about 0.015 inch (0.381 millimeters), and the third thickness  1530  may be about 0.050 inch (1.27 millimeters). Accordingly, the chamfer portion  1540  may accommodate some of the additional material when the face portion  162  is welded to the body portion  110 . 
     As illustrated in  FIG. 16 , for example, the face portion  162  may include a reinforcement section, generally shown as  1605 , below one or more grooves  168 . In one example, the face portion  162  may include a reinforcement section  1605  below each groove. Alternatively, face portion  162  may include the reinforcement section  1605  below some grooves (e.g., every other groove) or below only one groove. The face portion  162  may include a first thickness  1610 , a second thickness  1620 , a third thickness  1630 , and a chamfer portion  1640 . The groove  168  may have a groove depth  1625 . The reinforcement section  1605  may define the second thickness  1620 . The first and second thicknesses  1610  and  1620 , respectively, may be substantially equal to each other (e.g., T 1 =T 2 ). In one example, the first and second thicknesses  1610  and  1620 , respectively, may be about 0.030 inch (0.762 millimeters) (e.g., T 1 =T 2 =0.030 inch). The groove depth  1625  may be about 0.015 inch (0.381 millimeters), and the third thickness  1630  may be about 0.050 inch (1.27 millimeters). The groove  168  may also have a groove width. The width of the reinforcement section  1605  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  162  may vary in thickness at and/or between the top portion  180  and the sole portion  190 . In one example, the face portion  162  may be relatively thicker at or proximate to the top portion  180  than at or proximate to the sole portion  190  (e.g., thickness of the face portion  162  may taper from the top portion  180  towards the sole portion  190 ). In another example, the face portion  162  may be relatively thicker at or proximate to the sole portion  190  than at or proximate to the top portion  180  (e.g., thickness of the face portion  162  may taper from the sole portion  190  towards the top portion  180 ). In yet another example, the face portion  162  may be relatively thicker between the top portion  180  and the sole portion  190  than at or proximate to the top portion  180  and the sole portion  190  (e.g., thickness of the face portion  162  may have a bell-shaped contour). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. As described herein, the interior cavity  700  may be partially or fully filled with a filler material, which may be a polymer material, a bonding agent (such as an adhesive or epoxy material), or a combination of polymer material(s) and bonding agent(s) to at least partially provide structural support for the face portion  162 . In particular, the filler material may also provide vibration and/or noise dampening for the body portion  110  when the face portion  162  strikes a golf ball. Alternatively, the filler material may only provide vibration and/or noise dampening for the body portion  110  when the face portion  162  strikes a golf ball. In one example, the body portion  110  of the golf club head  100  (e.g., an iron-type golf club head) may have a body portion volume (V b ) between about 2.0 cubic inches (32.77 cubic centimeters) and about 4.2 cubic inches (68.83 cubic centimeters). The volume of the filler material filling the interior cavity (V e ), such as the interior cavity  700 , may be between 0.5 and 1.7 cubic inches (8.19 and 27.86 cubic centimeters, respectively). A ratio of the filler material volume (V e ) to the body portion volume (V b ) may be expressed as: 
     
       
         
           
             0.2 
             ≤ 
             
               
                 V 
                 e 
               
               
                 V 
                 b 
               
             
             ≤ 
             0.5 
           
         
       
         
         
           
             Where: V e  is the filler material volume in units of in 3 , and
           V b  is the body portion volume in units of in 3 .   
         
           
         
       
    
     In another example, the ratio of the filler material volume (V e ) to the body portion volume (V b ) may be between about 0.2 and about 0.4. In yet another example, the ratio of the filler material volume (V e ) to the body portion volume (V b ) may be between about 0.25 and about 0.35. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Based on the amount of filler material filling the interior cavity, for example, the thickness of the face portion may be between about 0.025 inches (0.635 millimeters) and about 0.1 inch (2.54 millimeters). In another example, the thickness of the face portion (T f ) may be between about 0.02 inches (0.508 millimeters) and about 0.09 inches (2.286 millimeters). The thickness of the face portion (T f ) may depend on the volume of the filler material in the interior cavity (V e ), such as the interior cavity  700 . The ratio of the thickness of the face portion (T f ) to the volume of the filler material (V e ) may be expressed as: 
     
       
         
           
             0.01 
             ≤ 
             
               
                 T 
                 f 
               
               
                 V 
                 e 
               
             
             ≤ 
             0.2 
           
         
       
         
         
           
             Where: T f  is the thickness of the face portion in units of inches, and
           V e  is the filler material volume in units of in 3 .   
         
           
         
       
    
     In one example, the ratio of the thickness of the face portion (T f ) to the volume of the filler material (V e ) may be between 0.02 and 0.09. In another example, the ratio of the thickness of the face portion (T f ) to the volume of the filler material (V e ) may be between 0.04 and 0.14. The thickness of the face portion (T f ) may be the same as T 1  and/or T 2  mentioned above. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The thickness of the face portion (T f ) may depend on the volume of the filler material in the interior cavity (V e ), such as the interior cavity  700 , and the body portion volume (V b ). The volume of the filler material (V e ) may be expressed as: 
     
       
      
       V 
       e 
       =a*V 
       b 
       +b±c*T 
       f  
      
         
         
           
             a≅0.48 
             b≅−0.38 
             0≦c≦10 
             Where: V e  is the filler material volume in units of in 3 , 
             V b  is the body portion volume in units of in 3 , and 
             T f  is the thickness of the face portion in units of inches. 
           
         
       
    
     As described herein, for example, the body portion volume (V b ) may be between about 2.0 cubic inches (32.77 cubic centimeters) and about 4.2 cubic inches (68.83 cubic centimeters). In one example, the thickness of the face portion (T f ) may be about 0.03 inches (0.762 millimeters). In another example, the thickness of the face portion (T f ) may be about 0.06 inches (1.524 millimeters). In yet another example, the thickness of the face portion (T f ) may be about 0.075 inches (1.905 millimeters). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Further, the volume of the filler material (V e ) when the interior cavity is fully filled with the filler material may be similar to the volume of the interior cavity (V c ). Accordingly, when the interior cavity is fully filled with a filler material, the volume of the filler material (V e ) in any of the equations provided herein may be replaced with the volume of the interior cavity (V c ). Accordingly, the above equations expressed in terms of the volume of the interior cavity (V c ) may be expressed as: 
     
       
         
           
             0.2 
             ≤ 
             
               Vc 
               Vb 
             
             ≤ 
             0.5 
           
         
       
       
         
           
             0.01 
             ≤ 
             
               Tf 
               Vc 
             
             ≤ 
             0.2 
           
         
       
       
         
           
             Vc 
             = 
             
               
                 a 
                 · 
                 Vb 
               
               + 
               
                 b 
                 ± 
                 
                   c 
                   · 
                   Tf 
                 
               
             
           
         
       
       
         
           
             a 
             ≅ 
             0.48 
           
         
       
       
         
           
             b 
             ≅ 
             
               - 
               0.38 
             
           
         
       
       
         
           
             0 
             ≤ 
             c 
             ≤ 
             10 
           
         
       
         
         
           
             Where: V c  is the volume of the interior cavity in units of in 3 ,
           V b  is the body portion volume in units of in 3 , and   T f  is the thickness of the face portion in units of inches.   
         
           
         
       
    
     As described herein, the filler material may include a bonding agent that may be bonded to the back surface  166  of the face portion  162  to attach the remaining portions of the filler material to the back surface  166  of the face portion  162 , dampen noise and vibration, provide a certain feel and sound for the golf club head, and/or at least partially structurally support the face portion  162 . The thickness of the bonding agent and/or a portion of the filler material may depend on a thickness of the face portion  162 . In one example, a relationship between a thickness of the face portion  162  and a thickness of a bonding agent and/or a portion of the filler material may be expressed as: 
     
       
         
           
             0.1 
             ≤ 
             
               Tf 
               
                 T 
                 a 
               
             
             ≤ 
             4.0 
           
         
       
         
         
           
             Where: 
             T f  is the thickness of the face portion in units of inches, and 
             T a  is the thickness of the bonding agent and/or the thickness of the filler material in units of inches. 
           
         
       
    
     In one example, the bonding agent and/or the filler material may have a thickness ranging from 0.02 inch (0.51 millimeters) to 0.2 inch (5.08 millimeters). In another example, the bonding agent and/or the filler material may be have a thickness ranging from 0.04 inch (0.1.02 millimeters) to 0.08 inch (2.03 millimeters). In another example, the bonding agent and/or the filler material may be have a thickness ranging from 0.03 inch (0.76 millimeters) to 0.06 inch (1.52 millimeters). In yet another example, the bonding agent and/or the filler material may have a thickness ranging from 0.01 inch (0.25 millimeters) to 0.3 inch (7.62 millimeters). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
       FIG. 17  depicts one manner in which the example golf club head described herein may be manufactured. In the example of  FIG. 17 , the process  1700  may begin with providing one or more mass portions, generally shown as the first and second sets of mass portions  120  and  130 , respectively (block  1710 ). The first set of mass portions  120  and/or the second set of mass portions  130  may be made of a first material such as a tungsten-based material, a titanium-based material, a steel-based material, an aluminum-based material, a non-metal material, any combination thereof, or other suitable type of materials. In one example, the mass portions of the first and second sets  120  and  130 , respectively, may be tungsten-alloy screws. 
     The process  1700  may provide a body portion  110  having the face portion  162 , the interior cavity  700 , and the back portion  170  with two or more ports, generally shown as  1420  and  1430  (block  1720 ). The body portion  110  may be made of a second material, which may be different than the first material or similar to the first material. The body portion  110  may be manufactured using an investment casting process, a billet forging process, a stamping process, a computer numerically controlled (CNC) machining process, a die casting process, any combination thereof, or other suitable manufacturing processes. In one example, the body portion  110  may be made of 17-4 PH stainless steel using a casting process. In another example, the body portion  110  may be made of other suitable type of stainless steel (e.g., Nitronic® 50 stainless steel manufactured by AK Steel Corporation, West Chester, Ohio) using a forging process. By using Nitronic® 50 stainless steel to manufacture the body portion  110 , the golf club head  100  may be relatively stronger and/or more resistant to corrosion than golf club heads made from other types of steel. One or more ports of the body portion  110  may include an opening and a port wall. For example, the port  1421  may include the opening  720  and the port wall  725  with the opening  720  and the port wall  725  being on opposite ends of each other. The interior cavity  700  may separate the port wall  725  of the port  1421  and the back surface  166  of the face portion  162 . In a similar manner, the port  1435  may include the opening  730  and the port wall  735  with the opening  730  and the port wall  735  being on opposite ends of each other. The interior cavity  700  may separate the port wall  735  of the port  1435  and the back surface  166  of the face portion  162 . 
     The process  1700  may couple one or more mass portions of the first and second sets of mass portions  120  and  130  into one of the one or more ports (blocks  1730 ). In one example, the process  1700  may insert and secure the mass portion  121  in the port  1421 , and the mass portion  135  in the port  1435 . The process  1700  may use various manufacturing methods and/or processes to secure the first set of mass portions  120  and/or the second set of mass portions  130  in the ports such as the ports  1421  and  1435  (e.g., epoxy, welding, brazing, mechanical lock(s), any combination thereof, etc.). 
     The process  1700  may partially or entirely fill the interior cavity  700  with a filler material, which may be one or a combination of a polymer material (e.g., an ethylene copolymer material such as DuPont™ HPF family of materials) (block  1740 ) and/or a bonding agent (e.g., an adhesive or epoxy material such as 3M™ Scotch-Weld™ Epoxy Adhesives DP100, DP100 Plus, DP100NS and DP100FR). In one example, the filler material may fill at least 50% of the interior cavity  700 . As mentioned above, the filler material may absorb shock, isolate vibration, and/or dampen noise in response to the golf club head  100  striking a golf ball. In one example, the interior cavity  700  may be filled with filler material, which may be a polymer material, a thermoplastic elastomer material, a thermoplastic polyurethane material, a bonding agent, and/or a combination thereof. In another example, the interior cavity  700  may be entirely filled with a bonding agent. As illustrated in  FIG. 18 , for example, the golf club head  100  may include one or more ports (e.g., one shown as  1431  in  FIG. 14 ) with a first opening  1830  and a second opening  1835 . The second opening  1835  may be used to access the interior cavity  700 . In one example, the process  1700  ( FIG. 17 ) may fill the interior cavity  700  with a filler material by injecting the filler material into the interior cavity  700  from the first opening  1830  via the second opening  1835 . The first and second openings  1830  and  1835 , respectively, may be same or different in size and/or shape. While the above example may describe and depict a particular port with a second opening, any other ports of the golf club head  100  may include a second opening (e.g., the port  1421 ). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Referring back to  FIG. 17 , the example process  1700  is merely provided and described in conjunction with other figures as an example of one way to manufacture the golf club head  100 . While a particular order of actions is illustrated in  FIG. 17 , these actions may be performed in other temporal sequences. For example, two or more actions depicted in  FIG. 17  may be performed sequentially, concurrently, or simultaneously. In one example, blocks  1710 ,  1720 ,  1730 , and/or  1740  may be performed simultaneously or concurrently. Although  FIG. 17  depicts a particular number of blocks, the process may not perform one or more blocks. In one example, the interior cavity  700  may not be filled (i.e., block  1740  may not be performed). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. Referring back to  FIGS. 1-14 , the face portion  162  may include a non-smooth back surface to improve adhesion and/or mitigate delamination between the face portion  162  and the elastic polymer material used to fill the interior cavity  700  (e.g.,  FIG. 7 ). Various methods and/or processes such as an abrasive blasting process (e.g., a bead blasting process, a sand blasting process, other suitable blasting process, or any combination thereof) and/or a milling (machining) process may be used to form the back surface  166  into a non-smooth surface. For example, the back surface  166  may have with a surface roughness (Ra) ranging from 0.5 to 250 μin (0.012 to 6.3 μm). The apparatus, methods, and articles of manufacture are not limited in this regard. 
     Referring to  FIG. 19 , for example, the golf club head  100  may include the face portion  162 , a bonding portion  1910 , and a polymer material  1920 . The bonding portion  1910  may provide connection, attachment and/or bonding of the polymer material  1920  to the face portion  162 . In one example, the bonding portion  1910  and/or the polymer material  1920  may define a filler material as described herein. The bonding portion  1910  may be a bonding agent such as any of adhesive or epoxy materials described herein, a tacky material, a combination of bonding agents, a bonding structure or attachment device (i.e., a physical and/or mechanical structure or device), a combination of bonding structures and/or attachment devices, and/or a combination of one or more bonding agents, one or more bonding structures and/or one or more attachment devices. The bonding portion  1910  may be integral with the polymer material  1920  to partially or entirely fill the interior cavity  700 . In other words, the polymer material  1920  may include inherent bonding properties. For example, the bonding portion  1910  may be a bonding agent mixed with the polymer material  1910  to provide bonding of the mixture to the back surface  166  of the face portion  162  and/or other inner surface(s) of the body portion  110 . In one example, the bonding portion may include one or more surface textures or surface structures on the back surface  166  of the face portion  162  to assist in adhesion of the polymer material to the back surface  166  of the face portion. The apparatus, methods, and articles of manufacture are not limited in this regard. 
     For example, the golf club head  100  may include a bonding agent such as any adhesive or epoxy materials described herein to improve adhesion and/or mitigate delamination between the face portion  162  and the polymer material  1920  used to fill the interior cavity  700  of the golf club head  100  (e.g.,  FIG. 7 ). The bonding portion  1910  may be applied to the back surface  166  of the face portion  162  to bond the polymer material  1920  to the face portion  162  (e.g., extending between the back surface  166  and the polymer material  1920 ). For example, the bonding portion  1910  may be applied before or during when the interior cavity  700  is filled with the polymer material  1920  via an injection molding process or other suitable process. The apparatus, methods, and articles of manufacture are not limited in this regard. 
       FIG. 20  depicts one manner to partially or entirely fill the interior cavity  700  of the golf club head  100  or any of the golf club heads described herein with a filler material. The process  2000  may begin with heating the golf club head  100  to a certain temperature (block  2010 ). In one example, the golf club head  100  may be heated to a temperature ranging between 150° C. and 250° C., which may depend on factors such as the vaporization temperature of the one or more components of the filler material to be injected in the interior cavity  700 . The filler material may then be heated to a certain temperature (block  2020 ). In one example, the filler material may be a non-foaming and injection-moldable thermoplastic elastomer (TPE) material. Accordingly, the filler material may be heated to reach a liquid or a flowing state prior to being injected into the interior cavity  700 . The temperature at which the filler material may be heated may depend on the type of polymer material used to form the filler material. The heated filler material may be injected into the interior cavity  700  to partially or fully fill the interior cavity  700  (block  2030 ). The filler material may be injected into the interior cavity  700  from one or more of the ports described herein (e.g., one or more ports of the first and second sets of ports  1420  and  1430 , respectively, shown in  FIG. 14 ). One or more other ports may allow the air inside the interior cavity  700  displaced by the filler material to vent from the interior cavity  700 . In one example, the golf club head  100  may be oriented horizontally as shown in  FIG. 14  during the injection molding process. The filler material may be injected into the interior cavity  700  from ports  1431  and  1432 . The ports  1421 ,  1422  and/or  1423  may serve as air ports for venting the displaced air from the interior cavity  700 . Thus, regardless of the orientation of the golf club head  100  during the injection molding process, the filler material may be injected into the interior cavity  700  from one or more lower positioned ports while one or more upper positioned ports may serve as air vents. The mold (e.g., the golf club head  100 ) may then be cooled passively (e.g., at room temperature) or actively so that the filler material reaches a solid state and adheres to the back surface  166  of the face portion  162 . The filler material may directly adhere to the back surface  166  of the face portion  162 . Alternatively, the filler material may adhere to the back surface  166  of the face portion  162  with the aid of the one or more structures on the back surface  166  and/or the bonding portion  1910  shown in  FIG. 19  (e.g., a bonding agent as described herein). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As described above, the filler material may be heated to a liquid state (i.e., non-foaming) and solidifies after being injection molded in the interior cavity  700 . A filler material with a low modulus of elasticity may provide vibration and/or noise dampening for the face portion  162  when the face portion  162  impacts a golf ball. For example, a polymer material that foams when heated may provide vibration and/or noise dampening. However, such a foaming polymer material may not have sufficient rigidity to provide structural support to a relatively thin face portion because of possible excessive deflection and/or compression of the polymer material when absorbing the impact of a golf ball. In one example, the one or more components of the filler material that is injection molded in the interior cavity  700  may have a relatively high modulus of elasticity to provide structural support to the face portion  162  and yet elastically deflect to absorb the impact forces experienced by the face portion  162  when striking a golf ball. Thus, a non-foaming and injection moldable polymer material with a relatively high modulus of elasticity may be used for partially or entirely filling the interior cavity  700  to provide structural support and reinforcement for the face portion  162  in addition to providing vibration and noise dampening. That is, the non-foaming and injection moldable polymer material may be a structural support portion for the face portion  162 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     As described herein, the filler material may include a bonding portion. The bonding portion may include an adhesive or epoxy material with a thickness to provide structural support for the face portion  162 . Accordingly, the filler material may include a foaming polymer material to provide vibration and noise dampening whereas the bonding portion may provide structural support for the face portion  162 . The thickness of the bonding portion may depend on a thickness and physical properties of the face portion  162  as described herein. The apparatus, methods, and articles of manufacture are not limited in this regard. 
     As described herein, the filler material may include a bonding agent (e.g., an adhesive or epoxy material) and a polymer material.  FIG. 21  depicts one manner in which a bonding agent as described herein may be applied to a golf club head prior to partially or entirely filling the interior cavity  700 . In the example of  FIG. 21 , the process  2100  may begin with injecting a bonding agent on the back surface  166  of the face portion  162  (block  2110 ). The bonding agent may be injected on the back surface  166  prior to or after heating the golf club head as described above depending on the properties of the bonding agent. The bonding agent may be injected through one or more of the first set of ports  1420  and/or the second set of ports  1430 . The bonding agent may be injected on the back surface  166  through several or all of the first set of ports  1420  and the second set of ports  1430 . For example, an injection instrument such as a nozzle or a needle may be inserted into each port until the tip or outlet of the instrument is near the back surface  166 . The bonding agent may then be injected on the back surface  166  from the outlet of the instrument. Additionally, the instrument may be moved, rotated and/or swiveled while inside the interior cavity  700  so that the bonding agent is injected onto an area of the back surface  166  surrounding the instrument. For example, the outlet of the injection instrument may be moved in a circular pattern while inside a port to inject the bonding agent in a corresponding circular pattern on the back surface  166 . Each of the first set of ports  1420  and the second set of ports  1430  may be utilized to inject a bonding agent on the back surface  166 . However, utilizing all of first ports  1420  and/or the second set of ports  1430  may not be necessary. For example, using every other adjacent port may be sufficient to inject a bonding agent on the entire back surface  166 . In another example, ports  1421 ,  1422   1431 ,  1433  and  1436  may be used to inject the bonding agent on the back surface  166 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The process  2100  may also include spreading the bonding agent on the back surface  166  (block  2120 ) after injection of the bonding agent onto the back surface  166  so that a generally uniform coating of the bonding agent is provided on the back surface  166 . According to one example, the bonding agent may be spread on the back surface  166  by injecting air into the interior cavity  700  through one or more of the first set of ports  1420  and the second set of ports  1430 . The air may be injected into the interior cavity  700  and on the back surface  166  by inserting an air nozzle into one or more of the first set of ports  1420  and the second set of ports  1430 . According to one example, the air nozzle may be moved, rotated and/or swiveled at a certain distance from the back surface  166  so as to uniformly blow air onto the bonding agent to spread the bonding agent on the back surface  166  for a uniform coating or a substantially uniform coating of the bonding agent on the back surface  166 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The example process  2100  is merely provided and described in conjunction with other figures as an example of one way to manufacture the golf club head  100 . While a particular order of actions is illustrated in  FIG. 21 , these actions may be performed in other temporal sequences. Further, two or more actions depicted in  FIG. 21  may be performed sequentially, concurrently, or simultaneously. The process  2100  may include a single action of injecting and uniformly or substantially uniformly coating the back surface  166  with the bonding agent. In one example, the bonding agent may be injected on the back surface  166  by being converted into fine particles or droplets (i.e., atomized) and sprayed on the back surface  166 . Accordingly, the back surface  166  may be uniformly or substantially uniformly coated with the bonding agent in one action (i.e., a substantially uniform coating of bonding agent particles, droplets or beads). A substantially uniform coating of the back surface  166  with the bonding agent may be defined as a coating having slight non-uniformities due to the injection process or the manufacturing process. However, such slight non-uniformities may not affect the bonding of the polymer material to the back surface  166  with the bonding agent as described herein. For example, spraying the bonding agent on the back surface  166  may result in overlapping regions of the bonding agent having a slightly greater coating thickness than other regions of the bonding agent on the back surface  166 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     As described herein, any two or more of the mass portions may be configured as a single mass portion. In the example of  FIGS. 22 and 23 , a golf club head  2200  may include a body portion  2210  and one or more mass portions, generally shown as a first set of mass portions  2220  (e.g., shown as mass portions  2221 ,  2222 ,  2223 , and  2224 ) and a second mass portion  2230 . The body portion  2210  may be made of a first material whereas the first set of mass portions  2220  and/or the second mass portion  2230  may be made of a second material. The first and second materials may be similar or different materials. The first and second materials of the body portion  2210  and/or the first and second mass portions  2220  and  2230 , respectively, may be similar to the first and second materials of the golf club head  100 . The body portion  2210  may include a toe portion  2240 , a heel portion  2250 , a front portion (not shown), a back portion  2270  with a back wall portion  2310 , a top portion  2280 , and a sole portion  2290 . The heel portion  2250  may include a hosel portion  2255  configured to receive a shaft (not shown) with a grip (not shown) on one end, and the golf club head  2200  on the opposite end of the shaft to form a golf club. The front portion may be similar to the front portion  160  of the golf club head  100 . Further, the golf club head  2200  may be the same type of golf club head as any of the golf club heads described herein. The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The body portion  2210  may include one or more ports along a periphery of the body portion  2210 , generally shown as a first set of ports  2320  (e.g., shown as ports  2321 ,  2322 ,  2323 , and  2324 ) and a second port  2330 . Each port of the first set of ports  2320  may be associated with a port diameter and at least one port of the first set of ports  2320  may be separated from an adjacent port similar to any of the ports described herein. The apparatus, methods, and articles of manufacture are not limited in this regard. 
     One or more mass portion of the first set of mass portions  2220  (e.g., shown as mass portions  2221 ,  2222 ,  2223 , and  2224 ) may be disposed in a port of the first set of ports  2320  (e.g., shown as ports  2321 ,  2322 ,  2323 , and  2324 ) located at or proximate to the toe portion  2240  and/or the top portion  2280  on the back portion  2270 . The physical properties and/or configurations of the first set of ports  2320  and the first set of mass portions  2220  may be similar to the golf club head  100 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The second port  2330  may have any configuration and/or extend to and/or between the toe portion  2240  and the heel portion  2250 . As illustrated in  FIG. 22 , for example, the second port  2330  may be a recess extending from the toe portion  2240  or a location proximate to the toe portion  2240  to the sole portion  2290  or a location proximate to the sole portion  2290 . Accordingly, the second port  2330  may resemble an L-shaped recess. The second mass portion  2230  may resemble the shape of the second port  2330  and may be disposed in the second port  2330 . The second mass portion  2230  may be partially or fully disposed in the second port  2330 . The second mass portion  2230  may have any shape such as oval, rectangular, triangular, or any geometric or non-geometric shape. The second port  2330  may be shaped similar to the second mass portion  2230 . However, portion(s) of the second mass portion  2230  that are inserted in the second port  2330  may have similar shapes as the second port  2330 . In one example (not shown), the second port  2330  may have a generally rectangular shape and located at or near the sole portion  2290  extending to and/or between the toe portion  2240  and the heel portion  2250 . Accordingly, at least a portion of the second mass portion  2230  may have a similar shape as the second port  2330 . As described herein, any of the mass portions described herein, including the first mass portions  2220  and the second mass portion  2230  may be coupled to the back portion  2270  of the body portion  2210  with various manufacturing methods and/or processes (e.g., a bonding process, a welding process, a brazing process, a mechanical locking method, any combination thereof, or other suitable manufacturing methods and/or processes). The second mass portion  2230  may be a polymer material that may be injection molded into the second port  2330  as described herein. Also as described herein, any of the mass portions described herein including the mass portion  2230  may be integral with the body portion  2210 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The second mass portion  2230  may affect the location of the CG of the golf club head  100  and the MOI of the golf club head about a vertical axis that extends through the CG of the golf club head  2200 . All or a substantial portion of the second mass portion  2230  may be generally near the sole portion  2290 . For example, the second mass portion  2230  may be near the periphery of the body portion  2210  and extend to and/or between the sole portion  2290  and the toe portion  2240 . As shown in the example of  FIG. 23 , the second mass portion  2230  may be located at or proximate to the periphery of the body portion  2210  and partially or substantially extend at or proximate to the sole portion  2290 . A portion of the second mass portion  2230  may be located near the periphery of the body portion  2210  and extend to and/or between the sole portion  2290  and the toe portion  2240  to lower the CG and increase the MOI of the golf club head  2200  about a vertical axis that extends through the CG. To lower the CG of the golf club head  2200 , all or a portion of the second mass portion  2230  may be located closer to the sole portion  2290  than to a horizontal midplane  2360  of the golf club head  2200 . The horizontal midplane  2360  may be vertically halfway between the ground and top planes  2355  and  2365 , respectively. The location of the second mass portion  2230  (i.e., the location of the second port  2330 ) and the physical properties and materials of construction of the mass portions of the second port  2230  may be determined to 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  2200 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As illustrated in  FIGS. 24-29 , a golf club head  2400  may include a body portion  2410 , and one or more mass portions, generally shown as a first set of mass portions  2420  (e.g., shown as mass portions  2421  and  2422 ), a second set of mass portions  2430  (e.g., shown as mass portions  2431 ,  2432 ,  2433 ,  2434 ,  2435 ,  2436 , and  2437 ), and a third mass portion  2412 . The third mass portion  2412  may be a continuous one-piece portion coupled to the body portion  2410 . In other words, the third mass portion  2412  may be integrally manufactured with the body portion  2410 . Alternatively, the third mass portion  2412  may be a separate piece from the body portion  2410  and is attached to the body portion  2410  as described herein. The second set of mass portions  2430  (e.g., shown as mass portions  2431 ,  2432 ,  2433 ,  2434 ,  2435 ,  2436 , and  2437 ) may be coupled to the third mass portion  2412  as described herein. The body portion  2410  may include a toe portion  2440 , a heel portion  2450 , a front portion  2460 , a back portion  2470 , a top portion  2480 , and a sole portion  2490 . The heel portion  2450  may include a hosel portion  2455  configured to receive a shaft (not shown) with a grip (not shown) on one end and the golf club head  2400  on the opposite end of the shaft to form a golf club. The front portion  2460  may include a face portion  2462  (e.g., a strike face). The body portion  2410  may be similar to the body portion of any of the golf club heads described herein. Further, the golf club head  2400  may be any type of golf club head such as any of the golf club heads described herein and be manufactured by any of the methods described herein (e.g., the process  1700  shown in  FIG. 17 ). The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The body portion  2410 , the first set of mass portions  2420 , the second set of mass portions  2430 , and/or the third mass portion  2412  may be made of similar or different materials. For example, the body portion  2410 , the first set of mass portions  2420 , the second set of mass portions  2430 , and/or the third mass portion  2412  may be made of steel, aluminum, titanium, tungsten, metal alloys, polymers, composite materials, or any combinations thereof. The material(s) of the golf club head  2400 , the first set of mass portions  2420 , the second set of mass portions  2430 , and/or the third mass portion  2412  may be similar to any of the golf club heads and the mass portions described herein such as the golf club head  100 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     Turning to  FIG. 25 , for example, the golf club head  2400  may be associated with a ground plane  2810 , a horizontal midplane  2820 , and a top plane  2830 . In particular, the ground plane  2810  may be a plane substantially parallel with the ground and tangential to the sole portion  2490  of the golf club head  2400  when the golf club head  2400  is at an address position (e.g., the golf club head  2400  is aligned to strike a golf ball). The top plane  2830  may be a tangential to the top portion  2480  of the golf club head  2400  when the golf club head  2400  is at the address position. The ground and top planes  2810  and  2830 , respectively, may be substantially parallel to each other. The horizontal midplane  2820  may be located at half the vertical distance between the ground and top planes  2810  and  2830 , respectively. 
     The third mass portion  2412  may be a portion of the golf club head  2400  made from a different material than the body portion  2410 . The third mass portion  2412  may be located on the back portion  2470  below the horizontal midplane  2820  of the golf club head  2400 . In one example (not shown), a portion of the third mass portion  2412  may be at or above the horizontal midplane  2820 . The third mass portion  2412  may be made of a material with a relatively greater density than the material of the body portion  2410  to lower the CG of the golf club head  2400  and/or to move the CG of the golf club head  2400  toward the back of the golf club head  2400 . In one example, the body portion  2410  may be made of a low density and high strength metal such as titanium or titanium alloy material(s), and the third mass portion  2412  may be made of a high density material such as tungsten or tungsten alloy material(s). In addition or alternatively, at least a portion of the body portion  2410  may be made of a high strength and low density material such as composite materials whereas the third mass portion  2412  may be made of a high density material such as tungsten material(s). Accordingly, the CG of the golf club head  2400  may be located lower than the CG of a comparable golf club head entirely made of a low density material such as titanium and/or composite material(s). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  2410  may include one or more ports along a periphery of the body portion  2410  or the back portion  2470 , generally shown as a first set of ports  2620  (e.g., shown as ports  2621  and  2622 ) and a second set of ports  2630  (e.g., shown as ports  2631 ,  2632 ,  2633 ,  2634 ,  2635 ,  2636  and  2637 ). One or more ports may be an opening of the body portion  2410 . The first set of ports  2620  and the second set of ports  2630 , respectively, may be ports configured to receive one or more mass portions of the first set of mass portions  2420  and/or the second set of mass portions  2430  similar to the example(s) of the golf club head  100  as described herein. The first set of ports  2620  (e.g., generally shown as ports  2621  and  2622 ) may be recesses or bores of the body portion  2410  configured to receive one or more mass portions of the first set of mass portions  2420  and/or mass portions of the second set of mass portions  2430 . The second set of ports  2630  (e.g., generally shown as ports  2631 ,  2632 ,  2633 ,  2634 ,  2635 ,  2636  and  2637 ) may be recesses or bores of the third mass portion  2412  configured to receive one or more mass portions of the first set of mass portions  2420  and/or mass portions of the second set of mass portions  2430 . One or more mass portions of the first and second sets of mass portions  2420  and  2430 , respectively, may be coupled to one or more ports of the first and second sets of ports  2620  and  2630 , respectively, with various manufacturing methods and/or processes (e.g., a bonding process, a welding process, a brazing process, a mechanical locking method, any combination thereof, or other suitable manufacturing methods and/or processes) such as the methods and processes described herein. The locations of the ports, the distances between the ports, the configurations and/or properties of the ports and the mass portions (e.g., dimensions and/or masses) may be similar to any of the golf club heads, ports and/or mass portions described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third mass portion  2412  may be made of a material with a relatively greater density than the material of the body portion  2410 . In one example, the third mass portion  2412  may be made of tungsten or tungsten alloy material(s) whereas the body portion  2410  may be made of titanium or titanium alloy material(s). Referring back to  FIG. 25 , for example, the third mass portion  2412  may be located below the horizontal midplane  2820  of the golf club head  2400  and on the back portion  2470  of the golf club head  2400  to place the CG of the golf club head  2400  lower and farther back as compared to a comparable golf club head substantially made of the same material as the material of the body portion  2410 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third mass portion  2412  may include a third mass-toe portion  2413 , a third mass-heel portion  2415  and a third mass-bottom portion  2417 . The third mass portion  2412  may extend to and/or between the toe portion  2440 , the heel portion  2450 , and/or the sole portion  2490 . For example, the third mass portion  2412  may extend to the toe portion edge  2441  of the toe portion  2440  of the golf club head  2400  so that the third mass portion  2412  may be a portion of the toe portion  2440  of the golf club head  2400  as shown in  FIG. 28 . The third mass portion  2412  may extend to the heel portion edge  2451  of the heel portion  2450  of the golf club head  2400  so that the heel portion  2415  of the third mass portion  2412  may be a portion of the heel portion  2450  of the golf club head  2400  as shown in  FIG. 29 . The third mass portion  2412  may extend to the bottom edge of the sole portion  2490  of the golf club head  2400  so that the third mass portion  2412  may be a portion of the sole portion  2490  of the golf club head  2400  as shown in  FIG. 27 . Accordingly, the third mass portion  2412  may be a portion of the golf club head  2400  extending to and/or between a location below the horizontal midplane  2820  of the golf club head and the sole portion  2490  of the golf club head  2400 , and extending to and/or between the toe portion  2440  and the heel portion  2450  of the golf club head  2400 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third mass-toe portion  2413  of the third mass portion  2412  may have a larger mass than the third mass-heel portion  2415  of the third mass portion  2412  to shift more mass toward the toe portion  2440  of the golf club head  2400  to increase the MOI of the golf club head  2400 . Accordingly, the third mass portion  2412  may have a relatively larger third mass-toe portion  2413  that may taper to a relatively smaller third mass-heel portion  2415 . The tapering of the third mass portion  2412  from the third mass-toe portion  2413  of the third mass portion  2412  to the third mass-heel portion  2415  of the third mass portion  2412  may be defined by a reduction in the height, a reduction in the width and/or a reduction in size and/or shape of the cross sectional area of the third mass portion  2412 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the third mass-heel portion  2415  of the third mass portion  2412  at or proximate to the heel portion  2450  of the golf club head  2400  may include a material with a relatively lower density than the remaining material of the third mass portion  2412  to lower the mass of the golf club head  2400  at or proximate to the heel portion  2450  and/or to provide more mass at or proximate to the toe portion  2440  of the golf club head  2400 . In one example, the body portion  2410  may be made of a material with a relatively greater density than titanium or titanium alloy material(s) such as steel material. Accordingly, the third mass portion  2412  may include a reduced mass portion at or proximate to the heel portion  2450  of the golf club head  2400  to lower the mass of the golf club head  2400  at or proximate the heel portion  2450  to balance the golf club head  2400  and move the CG toward a center portion of the golf club head  2400 . For example, a portion of the third mass portion  2412  at or proximate to the third mass-heel portion  2415  of the third mass portion  2412  may include a portion (not shown) that may include a material with a relatively lower density than the remaining material of the third mass portion  2412 . In one example, a portion of the third mass portion  2412  at or proximate to the third mass-heel portion  2415  of the third mass portion  2412  may include aluminum or aluminum alloy material(s). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The third mass portion  2412  may be a separate piece from the body portion  2410  and may be removed from the body portion  2410 . Accordingly, the third mass portion  2412  may be removed and exchanged with another third mass portion  2412  having a different mass to allow for adjustability of the mass distribution and/or the total mass of the golf club head  2400 . The third mass portion  2412  may be attached to the body portion  2410  by one or more mass portions of the second set of mass portions  2430 . For example, one or more of the ports of the second set of ports  2630  may be through bores of the third mass portion  2412  that align with corresponding recesses or bores (not shown) on the body portion  2410 . One or more mass portions of the second set of mass portions  2430  may be inserted into the one or more ports of the second set of ports  2630  and extend through the recesses or bores on the body portion  2410  to fasten the third mass portion  2412  to the body portion  2410 . The second set of mass portions  2430  (e.g., mass portions  2431 ,  2432 ,  2433 ,  2434 ,  2435 ,  2436  and  2437 ) may be configured to place the CG of the golf club head  2400  at an optimal location and/or optimize the MOI of the golf club head about a vertical axis (not shown) that extends through the CG of the golf club head  2400  similar to the second mass portions  130  of the golf club head  100 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the body portion  2410  or any of the body portions of the golf club heads described herein may be made of one or more metal or metal alloy material(s), non-metallic materials such as composite materials, plastic materials, or wood, and/or any combinations thereof. The third mass portion  2412  may be made of a material that has a greater density than the material of the body portion  2410 . For example, the body portion  2410  may be made of titanium or titanium alloy material(s) whereas the third mass portion  2412  may be made of tungsten or tungsten alloy material(s). Accordingly, the hosel portion  2455  may be made of the same material as the material of the body portion  2410  or a different material. To balance the mass of the golf club head  2400  due to the hosel portion  2455  being made of a low-density metal material such as titanium or titanium alloy material(s), the golf club head  2400  may include hosel mass portions  2467  and  2469 . The hosel mass portion  2467  may be permanently attached to the hosel portion  2465  whereas the hosel mass portion  2469  may be removable and exchangeable with other hosel mass portions to balance the mass of the golf club head  2400  at the hosel portion  2465 . The hosel mass portions  2467  and  2469  may be a fourth set of mass portions for the golf club head  2400 . Accordingly, the golf club head  2400  may include a first set of mass portions  2420  and/or a fourth set of mass portions defined by the hosel mass portions  2467  and  2469  above or proximate to the horizontal midplane  2820 , and a second set of mass portions  2430  and/or a fourth mass portion below or proximate to the horizontal midplane  2820 . In one example, the hosel mass portions  2467  and  2469  and the first set of mass portions  2420  may be collectively the first set of mass portions, and the second set of mass portions  2430  and the third mass portion  2412  may be collectively the second set of mass portions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The mass portions of the second set of mass portions  2430  may have similar or different masses. In one example, the mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435  may be made of a material with a relatively lower density than the mass portions  2436  and  2437 . For example, the mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435  may be made of titanium or titanium alloy material(s), while the mass portions  2436  and  2437  may be made of tungsten or tungsten alloy material(s). The mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435  may be changed with mass portions having relatively greater or less mass to affect the swing weight of the golf club head  2400 . Accordingly, the total mass of the mass portions  2436  and  2437  may be greater than the total mass of the mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435  to increase the MOI of the golf club head  2400 . In one example, the mass of one or more of the mass portions may progressively increase from the heel portion  2450  to the toe portion  2440 . In another example, the mass of one or more of the mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435  may progressively increase from the heel portion  2450  to the toe portion  2440  whereas the mass of one or more the mass portions  2436  and  2437  may be constant and greater than the mass of any of the mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435 . In yet another example, each of the mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435  may have similar masses, and each of the mass portions  2436  and  2437  may also have similar masses but greater than the mass of any of the mass portions  2431 ,  2432 ,  2433 ,  2434  and  2435 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Alternatively, two or more mass portions in the same set may be different in mass. In one example, the mass portion  2421  of the first set  2420  may have a relatively less mass than the mass portion  2422  of the first set  2420 . In another example, the mass portion  2431  of the second set  2430  may have a relatively less mass than the mass portion  2435  of the second set  2430 . Accordingly, more mass may be distributed away from the heel portion  2450  to increase the MOI about the vertical axis through the CG. 
     While the figures may depict ports with a particular cross-section shape, the apparatus, methods, and articles of manufacture described herein may include ports with other suitable cross-section shapes. The ports of the first and/or second sets of ports  2620  and  2630 , respectively, may have cross-sectional shapes that are similar to the cross-sectional shapes of any of the ports described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first and second sets of mass portions  2420  and  2430 , respectively, may be similar in mass (e.g., all of the mass portions of the first and second sets  2420  and  2430 , respectively, may weigh about the same). Alternatively, one or more mass portions of the first and second sets of mass portions  2420  and  2430 , respectively, may be different in mass individually or as an entire set. In particular, one or more mass portions of the first set  2420  (e.g., shown as  2421  and  2422 ) may have relatively less mass than any of the mass portions of the second set  2430  (e.g., shown as  2431 ,  2432 ,  2433 ,  2434 ,  2435 ,  2436  and  2437 ). For example, the second set of mass portions  2430  may account for more than 41% of the total mass of the mass portion(s) of the golf club head  2400 . In another example, the second set of mass portions  2430  may account for between 55% and 75% of the total mass of the mass portion(s) of the golf club head  2400 . In yet another example, the second set of mass portions  2430  may account for between 60% and 90% of the total mass of the mass portion(s) of the golf club head  2400 . As a result, the golf club head  2400  may be configured to have at least 41% of the total mass of the mass portion(s) disposed below the horizontal midplane  2820 . Further, the total mass of the mass portion(s) may be greater below the horizontal midplane  2820  that the total mass of the mass portion(s) above the horizontal midplane  2820 . The mass of the body portion  2410 , one or more mass portions of the first set of mass portions  2420 , the total mass of the first set of mass portions  2420 , one or more mass portions of the second set of mass portions  2430 , and/or the total mass of the second set of mass portions  2430  may be similar to the golf club head  100  as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     With the first and second sets of mass portions  2420  and  2430 , (e.g., securing the first and second sets of mass portions  2420  and  2430  in the ports on the body portion  2410  and/or having first and second sets of mass portion being integral with the body portion  2410 ), and having the third mass portion  2412  being made of a material with a relatively greater density than the material of the body portion  2410 , the location of the CG and the MOI of the golf club head  2400  may be optimized. In particular, the third mass portion  2412  and the first and second sets of mass portions  2420  and  2430 , respectively, may lower the location of the CG towards the sole portion  2490  and further back away from the face portion  2462 . Further, the MOI may be higher as measured about a vertical axis extending through the CG (e.g., perpendicular to the ground plane  2810 ). The MOI may also be higher as measured about a horizontal axis extending through the CG (e.g., extending towards the toe and heel portions  2450  and  2460 , respectively, of the golf club head  2400 ). As a result, the club head  2400  may provide a relatively higher launch angle and a relatively lower spin rate than a golf club head without the third mass portion  2412  and the first and second sets of mass portions  2420  and  2430 , respectively. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Although the figures may depict the mass portions as separate and individual parts visible from an exterior of the golf club head  2400 , one or more mass portions of the first set of mass portions  2420  and/or the second set of mass portions  2430 , respectively, may be a single piece of an exterior mass portion and/or an interior mass portion (e.g., not visible from an exterior of the golf club head  100 ). In one example, all of the mass portions of the first set  2420  (e.g., shown as  2421  and  2422 ) may be combined into a single piece of mass portion (e.g., a first mass portion). In a similar manner, all of the mass portions of the second set  2430  (e.g.,  2431 ,  2432 ,  2433 ,  2434 ,  2435 ,  2436  and  2437 ) may be combined into a single piece of mass portion as well (e.g., a second mass portion). In this example, the golf club head  2400  may have only two mass portions. In another example (not shown), the body portion  2410  may not include the first set of mass portions  2420 , but include the second set of mass portions  2430  as a single piece of interior mass portion located farther from the heel portion  2450  than the toe portion  2440 . In yet another example (not shown), the body portion  2410  may not include the first set of mass portions  2420 , but include the second set of mass portions  2430  with a first interior mass portion located farther from the heel portion  2450  than the toe portion  2440  and a second interior mass portion located farther from the toe portion  2440  than the heel portion  2450 . The first interior mass portion and the second interior mass portion may be (i) integral parts of the body portion  2410  or (ii) separate from the body portion  2410  and coupled to the body portion  2410 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  2410  of the golf club head  2400  may be a hollow body including the interior cavity (not shown) similar to the golf club head  100 . Further, the interior cavity may be unfilled, partially filled with one or more filler materials, or entirely filled with one or more filler materials similar to the golf club head  100  as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Referring back to  FIGS. 24-29 , for example, the back portion  2470  may include a channel  2710  with a length extending to and/or between the toe portion  2440  and the heel portion  2450 . The channel  2710  may extend parallel (not shown) to the horizontal midplane  2820  or extend at an angle relative to the horizontal midplane  2820  as shown in the example of  FIG. 25 . The channel  2710  may extend from a location at or proximate to the toe portion edge  2441  of the toe portion  2440  at or near the horizontal midplane  2820  to a location at or proximate to the heel portion edge  2451  of the heel portion  2450  below the horizontal midplane  2820 . In one example (not shown), the channel  2710  may extend from the toe portion edge  2441  to a location between the toe portion  2440  and the heel portion  2450 . In another example (not shown), the channel  2710  may extend from the heel portion edge  2451  of the heel portion  2450  to a location between the toe portion  2440  and the heel portion  2450 . In yet another example, the channel  2710  may partially extend to and/or between the toe portion  2440  and the heel portion  2450 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, as shown in  FIGS. 24-29 , the top channel width (W CT )  2716  may decrease in a direction from the toe portion  2440  to the heel portion  2450 . The top channel width  2716  may be between 0.22 inch (0.55 cm) and 0.65 inch (1.66 cm) at the toe portion edge  2441 , and between 0.15 inch (0.29 cm) and 0.37 inch (1.16 cm) at the heel portion edge  2451 . In another example, the top channel width  2716  may be between 0.30 inch (0.77 cm) and 0.57 inch (1.35 cm) at the toe portion edge  2441 , and between 0.21 inch (0.54 cm) and 0.31 inch (1.01 cm) at the heel portion edge  2451 . In another example, the top channel width  2716  may be between 0.28 inch (0.94 cm) and 0.5 inch (1.27 cm) at the toe portion edge  2441 , and between 0.26 inch (0.66 cm) and 0.26 inch (0.89 cm) at the heel portion edge  2451 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The top channel width  2716  may decrease in a direction from the toe portion edge  2441  to the heel portion edge  2451 . In another example, the top channel width  2716  may increase in a direction from the toe portion edge  2441  to the heel portion edge  2451 . In yet another example, the top channel width  2716  may remain constant in a direction from the toe portion edge  2441  to the heel portion edge  2451 . The top channel width  2716  may vary in any manner in a direction from the toe portion edge  2441  to the heel portion edge  2451 . For example, the top channel width  2716  may vary in a direction from the toe portion edge  2441  to the heel portion edge  2451  by between 25% and 75% of the top channel width  2716  at or proximate to the toe portion edge  2441 . In another example, the top channel width  2716  may vary in a direction from the toe portion edge  2441  to the heel portion edge  2451  by between 26% and 65%. In another example, the top channel width  2716  may vary in a direction from the toe portion edge  2441  to the heel portion edge  2451  by between 31% and 60%. In yet another example, the top channel width  2716  may decrease continuously and uniformly in a direction from the toe portion edge  2441  to the heel portion edge  2451  (shown in  FIGS. 24-29 ). In yet another example, the top channel width  2716  may increase continuously and uniformly in a direction from the toe portion edge  2441  to the heel portion edge  2451  (not shown). In yet another example, the top channel width  2716  may change in a discontinuous or step-wise manner (not shown) in a direction from the toe portion edge  2441  to the heel portion edge  2451  (not shown). The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As illustrated in the example of  FIGS. 24-29 , the channel  2710  may include a first groove portion  2718 , a first step portion  2719 , a second groove portion  2720 , and a second step portion  2721 . Each of the first and second groove portions  2718  and  2720 , respectively, may include side walls that form a generally right angle, an acute angle, or an obtuse angle relative to the channel width  2716  or a bottom portion of each groove portion, respectively. Accordingly, the groove portions  2718  and  2720  may define valley-shaped groove portions. The areas of joinder between the sidewalls of the groove portions  2718  and  2720  and the bottom portion of each groove portion may include a chamfer or a transition region. The channel  2710  may have any shape or configuration. In one example, the channel  2710  may have U-shaped cross section along a portion or the entire length of the channel  2710 . In another example, the channel  2710  may have a square or rectangular cross section along a portion or the entire length of the channel  2710 . In yet another example, the channel  2710  may be a longitudinal recess in the body portion  2410  without having any multiple groove and or step portions. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The depth each groove portion  2718  and  2720  may be generally constant or may vary in a direction from the toe portion edge  2441  to the heel portion edge  2451 . In one example, the depth each groove portion  2718  and/or  2720  may decrease in a direction from the toe portion edge  2441  to the heel portion edge  2451 . In another example, as shown in  FIGS. 24-29 , the depth each groove portion  2718  and/or  2720  may increase in a direction from the toe portion edge  2441  to the heel portion edge  2451 . In one example, the depth each groove portion  2718  and/or  2720  may be between 0.04 inch (0.09 cm) and 0.11 inch (0.28 cm) at the toe portion edge  2441  and between 0.06 inch (0.16 cm) and 0.19 inch (0.48 cm) at the heel portion edge  2451 . In another example, the depth each groove portion  2718  and/or  2720  may be between 0.05 inch (0.13 cm) and 0.09 inch (0.24 cm) at the toe portion edge  2441  and between 0.09 inch (0.22 cm) and 0.16 inch (0.32 cm) at the heel portion edge  2451 . In another example, the depth each groove portion  2718  and/or  2720  may be between 0.06 inch (0.16 cm) and 0.08 inch (0.21 cm) at the toe portion edge  2441  and between 0.11 inch (0.27 cm) and 0.14 inch (0.28 cm) at the heel portion edge  2451 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The first step portion  2719  may define a transition portion between the first groove portion  2718  and the second groove portion  2720 . The second step portion  2719  may define a transition portion between the second groove portion  2720  and the portion back wall portion  2610  below the channel  2710 . The width of the first step portion  2719  and/or the second step portion  2721  may be generally constant or may vary in a direction from the toe portion edge  2441  to the heel portion edge  2451 . In one example, the width of the first step portion  2719  and/or the second step portion  2721  may decrease in a direction from the toe portion edge  2441  to the heel portion edge  2451 . In another example, the width of the first step portion  2719  and/or the second step portion  2721  may increase in a direction from the toe portion edge  2441  to the heel portion edge  2451 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The channel  2710  may define a portion of the body portion  2410  from which mass has been removed to form the channel  2710 . The removed mass defined by the channel  2710  may be redistributed to other portions of the body portion  2410  to provide certain characteristics to the golf club head  2400 . At least a portion of the removed mass defined by the channel  2710  may be redistributed below the horizontal midplane  2820  of the body portion  2410  to lower the CG of the golf club head  2400  while maintaining or substantially maintaining the overall mass of the body portion  2410 . Further, at least a portion of the removed mass defined by the channel  2710  may be redistributed below the horizontal midplane  2820  of the body portion  2410  and closer to the toe portion  2440  than the heel portion  2450  to increase the MOI of the golf club head  2400 . In one example, the removed mass defined by the channel  2710  may be redistributed and incorporated into the body portion  2410  below the horizontal midplane  2820  by increasing the volume of the body portion  2410  below the horizontal midplane  2820 . Accordingly, the volume and the mass of the body portion  2410  below the horizontal midplane  2820  may be increased. In another example, the removed mass defined by the channel  2710  may be redistributed and incorporated into the third mass portion  2412 . In another example, the removed mass defined by the channel  2710  may be redistributed and incorporated into the body portion  2410  as additional mass portion(s). The increased mass below the horizontal midplane  2820  and/or toward the toe portion  2440  may lower the CG and/or increase the MOI of the golf club head  2400 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. The configuration of the channel  2710 , such as width, depth, volume, cross-sectional shape, and/or any other characteristics described herein may vary as the channel  2710  extends to and/or between the toe portion  2440  and the heel portion  2450 . Accordingly, the mass that is removed from the body portion  2410  due to the presence of the channel  2710  may similarly vary. According to another example, the masses of one or more of the mass portions of the second set of mass portions  2430  may correspondingly vary in a direction from the toe portion  2440  to the heel portion  2450  at a similar rate, a substantially similar rate, or a discrete and step-wise (e.g., mass portions varying in groups of multiple mass portions) yet generally similar rate as the variation in the channel configuration in a direction from the toe portion  2440  to the heel portion  2450 . In yet another example, all of the mass portions of the second set of mass portions  2430  may have similar masses. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The masses of one or more of the mass portion(s) of the first set of mass portions  2420  and/or the second set of mass portions  2430  may vary. The mass of one or more mass portion(s) may be increased and/or decreased by changing the length, diameter, and/or the material(s) of construction of the mass portions. For example, the mass of a mass portion may be increased by increasing the length of the mass portion without increasing the diameter of the mass portion so that the mass portion can be used in any of the ports of the body portion  2410 . In another example, the mass of a mass portion may be increased by using a material with a relatively greater density for the mass portion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     In one example, the masses of one or more mass portion(s) the second set of mass portions  2430  may decrease in a direction from the toe portion  2440  to the heel portion  2450  to increase the MOI of the golf club head  2400 . In one example, one or more mass portion(s) of the mass portions of the second set of mass portions  2430  may have a lower mass relative to an adjacent mass portion of the second set of mass portions  2430  in a direction from the toe portion  2440  to the heel portion  2450 . In another example, groups of mass portions of the second set of mass portions  2430  may have similar masses and yet have a smaller overall mass than an adjacent group of mass portions in a direction from the toe portion  2440  to the heel portion  2450 . Accordingly, the masses of the mass portions of the second set of mass portions  2430  may decrease in a direction from the toe portion  2440  to the heel portion  2450  individually, in groups or in any manner. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Turning to  FIGS. 30-38 , a golf club head  3000  may include a body portion  3010 . The body portion  3010  may include a toe portion  3040 , a heel portion  3050 , a front portion  3060 , a back portion  3070 , a top portion  3080 , and a sole portion  3090 . The heel portion  3050  may include a hosel portion  3055  configured to receive a shaft (not shown) with a grip (not shown) on one end and the golf club head  3000  on the opposite end of the shaft to form a golf club. The front portion  3060  may include a face portion  3062  (e.g., a strike face). The golf club head  3000  may be any type of golf club head such as any of the golf club heads described herein and be manufactured by any of the methods described herein and illustrated in  FIG. 17 . The golf club head  3000  may be similar to the golf club head  100 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The body portion  3010  may include one or more mass portions, generally shown as a first set of mass portions  3020  (e.g., shown as mass portions  3021  and  3022 ), a second set of mass portions  3030  (e.g., shown as mass portions  3031 ,  3032 ,  3033 ,  3034 ,  3035 , and  3036 ), and a third mass portion  3012 . The body portion  3010  may include one or more ports along a periphery of the body portion  3010 , generally shown as a first set of ports  3220  (e.g., shown as ports  3221  and  3222 ) and a second set of ports  3230  (e.g., shown as ports  3231 ,  3232 ,  3233 ,  3234 ,  3235 , and  3236 ). The body portion  3010 , the first set of ports  3220 , the second set of ports  3230 , the first set of mass portions  3020 , and the second set of mass portions  3030  may be similar to the corresponding parts of the golf club heads  100  and/or  2400 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     As shown in  FIGS. 30-34 , for example, the third mass portion  3012  may be an integral part of the body portion  3010  and made of one or more material(s) that are similar to or different from the material(s) of the body portion  3010 . In another example, the third mass portion  3012  may be similar to the third mass portion  2412  of the golf club head  2400 . Accordingly, in one example (not shown), the third mass portion  3012  may be a separate piece from the body portion  3010  and may be removable from the body portion  3010 . In another example, all or portion(s) of the third mass portion  3012  may be made of similar material(s) as the third mass portion  2412 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The back portion  3070  may include a channel  3310  with a length extending in a direction from the toe portion  3040  to the heel portion  3050 . The channel  3310  may be similar to the channel  2710  of the golf club head  2400 . The channel  2710  of the golf club head  2400  may extend from the toe portion  2440  to the heel portion  2450  at an angle relative to the horizontal midplane  2820  as shown in the example of  FIG. 25 . The channel  3310  may similarly extend from the toe portion  3040  of the body portion  3010  toward the heel portion  3050 . The channel  3310 , however, may include a portion  3311  proximate to the heel portion  3050  that extends toward the heel portion  3050  and the sole portion  3090 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The body portion  3010  of the golf club head  3000  may be a hollow body portion including an interior cavity  3700  similar to the body portion  110  of the golf club head  100 . Further, the interior cavity  3700  may be unfilled, partially filled with one or more filler materials, or entirely filled with one or more filler materials similar to the interior cavity  700  of the golf club head  100  as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     For example, as shown in  FIGS. 35-39 , the interior cavity  3700  may include a first inner perimeter portion  3702  proximate to the front portion  3060  with a first inner perimeter portion height (H PP1 )  3704  and a second inner perimeter portion  3712  located more forward that the first inner perimeter portion  3702  with a second inner perimeter portion height (H PP2 )  3714 . The second inner perimeter portion height  3714  may define the largest dimension of the interior cavity  3700  in a direction from the top portion  3080  to the sole portion  3090 . The second inner perimeter portion height  3714  may be greater than the first inner perimeter portion height  3704  to define an undercut portion  3722  at or near the front portion  3060 . The front portion  3060  may have a front edge height (H FE )  3061 , which may define the height of the most forward part of the front portion  3060 . Accordingly, the front portion  3060  may include a perimeter ledge portion  3732  with a perimeter ledge portion width (W PLP )  3734 . The perimeter ledge portion width  3734  may be the difference between the front edge height  3061  and the second inner perimeter portion height  3714  (e.g., W PLP =H FE −H PP2 ). The perimeter ledge portion width  3734  may extend around all or portion(s) of the front portion  3060  in a continuous or discontinuous manner (e.g., including segments and/or gaps). The perimeter ledge portion  3732  may define an outer boundary of the front portion  3060 . The perimeter ledge portion  3732  may be an exterior surface portion of the body portion  3010  at the front portion  3060  outside the interior cavity  3700  and forward of the undercut portion  3722 . Any one or more of the transition regions between the first inner perimeter portion  3702 , the second inner perimeter portion  3712 , the undercut portion  3722 , and the perimeter ledge portion  3732  may be configured to reduce stress concentration areas at or proximate to the transition regions and/or the attachment area of the face portion  3062  to the perimeter ledge portion  3732 . For example, the transition region between the undercut portion  3722  and the perimeter ledge portion  3732  may be chamfered to reduce the stress on the face portion  3062  when the face portion  3062  strikes a golf ball. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As illustrated in  FIG. 38 , for example, the configuration (e.g., dimensions, cross-sectional shape, etc.) of the undercut portion  3722  at or proximate to any location around the perimeter of the front portion  3060  may determine the configuration of the perimeter ledge portion  3732  including the perimeter ledge portion width  3734  at or proximate to that particular location. The undercut portion  3722  may have an undercut portion height (H UC )  3736  and an undercut portion depth (D UC )  3738  at or proximate to any location around the perimeter of the front portion  3060 . In one example, the undercut portion height  3736  may be between about 0.05 inch (1.27 millimeters) and about 0.15 inch (3.81 millimeters), and the undercut portion depth  3738  may be between about 0.06 inch (1.52 millimeters) and about 0.14 inch (3.56 millimeters) at or proximate to one or more locations around the perimeter of the front portion  3060 . In another example, the undercut portion height  3736  may be between about 0.075 inch (1.08 millimeters) and about 0.125 inch (3.18 millimeters), and the undercut portion depth  3738  may be between about 0.08 inch (2.03 millimeters) and about 0.12 inch (3.05 millimeters) at or proximate to one or more locations around the perimeter of the front portion  3060 . In yet another example, the undercut portion height  3736  may be between about 0.09 inch (2.29 millimeters) and about 0.11 inch (2.79 millimeters), and the undercut portion depth  3738  may be between about 0.09 inch (2.29 millimeters) and about 0.11 inch (2.79 millimeters) at or proximate to one or more locations around the perimeter of the front portion  3060 . The undercut portion height  3736  and/or the undercut portion depth  3738  may be less than or greater than the ranges described herein. The configuration (e.g., dimensions, cross-sectional shape, etc.) of the undercut portion  3722  may be constant or vary around the perimeter of the front portion  3060 . For example, the undercut portion  3722  may have an undercut portion height  3736  of 0.1 inch (2.54 millimeters) at or around at one location on the front portion  3060  but an undercut portion height  3736  of 0.075 inch (1.91 millimeters) at or around another location on the front portion  3060 . The configuration (e.g., dimensions, cross-sectional shape, etc.) of the undercut portion  3722  may be constant or vary for different types of golf club heads. For example, different iron-type golf club heads may have similar or different configuration (e.g., dimensions, cross-sectional shape, etc.) of the undercut portion  3722 . While the figures may depict a substantially right-angle undercut portion, the apparatus, methods, and articles of manufacture described herein may include a radiused undercut portion. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The face portion  3062  may have a face portion height (H FP )  3063 , which may be similar to the front edge height (H FE )  3061 . Accordingly, the perimeter ledge portion  3732  may define a surface for the face portion  3062  to attach to the body portion  3010 . The face portion  3062  may be attached to the perimeter ledge portion  3732  by welding, soldering, using one or more adhesives, and/or other suitable methods. In another example, the face portion  3062  may be an integral part of the body portion  3010 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     As mentioned above, the difference between the front edge height  3061  and the second inner perimeter portion height  3714  may define the perimeter ledge portion width  3734 . Accordingly, the configuration of the undercut portion  3722  may determine the perimeter ledge portion width  3734  and other configuration(s) of the perimeter ledge portion  3732 . As mentioned above, the face portion  3062  may attach to the front portion  3060  of the body portion  3010 . The face portion  3062  may include a face perimeter portion  3066  to attach to the perimeter ledge portion  3732  of the front portion  3060 . The face portion  3062  may include a strike portion  3067 , which may extend from opposing sides of the perimeter ledge portion  3732 . The strike portion  3067  of the face portion  3062  may be a portion of the face portion  3062  that bends as the face portion  3062  strikes a golf ball (not shown). In another example, the strike portion  3067  may include one or more grooves. The height of the strike portion  3067  may be similar to the second inner perimeter portion height  3714 . The location of the perimeter ledge portion  3732  and the perimeter ledge portion width  3734  may provide a relatively large face portion strike portion  3067  (e.g., large second inner perimeter portion height  3712 ) to provide relatively greater flexibility to strike a golf ball. The undercut portion  3722  may be made as large as possible considering the physical characteristics and materials of the golf club head  3000  and/or the face portion  3062  (e.g., face portion thickness) to provide a perimeter ledge portion  3732  with as small as possible perimeter ledge portion width  3734  to increase the size of the face portion strike portion  3067  as much as possible. The increased size of the strike portion  3067  of the face portion  3062  may increase ball speed and/or distance for an individual using the golf club head  3000 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     The perimeter ledge portion width  3734  may be constant or vary along the perimeter of the front portion  3060 . In one example, the perimeter ledge portion width  3734  may be constant in a range between about 0.04 inch (1.02 millimeters) and about 0.14 inch (3.56 millimeters). In another example, the perimeter ledge portion width  3734  may be constant in a range between about 0.06 inch (1.52 millimeters) and about 0.12 inch (3.05 millimeters). In yet another example, the perimeter ledge portion width  3734  may be constant in a range between and about 0.08 inch (2.03 millimeters) and about 0.1 inch (2.54 millimeters). In addition or alternatively, the perimeter ledge portion width  3734  may vary along the perimeter of the front portion  3060  in any of the width ranges described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     Although the figures may depict and the above examples may describe particular dimensions, the first inner perimeter portion  3702 , the second inner perimeter portion  3712 , the undercut portion  3722 , the perimeter ledge portion  3732 , and/or the face portion  3062  may vary in lengths, widths, etc. The configurations of the first inner perimeter portion  3702 , the second inner perimeter portion  3712 , the undercut portion  3722 , the perimeter ledge portion  3732 , and/or the face portion  3062  described herein may be applicable along a width  3802  of the front portion  3060  (e.g., as shown in  FIG. 37 ). Further, the configurations of the first inner perimeter portion  3702 , the second inner perimeter portion  3712 , the undercut portion  3722 , the perimeter ledge portion  3732  and/or the face portion  3062  described herein may be applicable along all or parts of the perimeter of the front portion  3060 . The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     For brevity, the description of processes described herein with reference to  FIGS. 40-42  may be provided in reference to the golf club head  100 . However, any apparatus, methods, and articles of manufacture described herein is applicable to any of the golf club heads described herein.  FIG. 40  depicts one manner that the interior cavity of any of the golf club heads described herein may be partially or entirely filled with one or more filler materials such as any of the filler materials described herein. The example process  4000  may begin with bonding a bonding agent to the back surface  166  of the face portion  162  of the golf club head  100  (block  4010 ). The bonding agent may have an initial bonding state, which may be a temporary bonding state, and a final bonding state, which may be a permanent bonding state. The initial bonding state and the final bonding states may be activated when the bonding agent is exposed to heat, radiation, and/or other chemical compounds. For example, as described herein, the bonding agent may be an epoxy having an initial cure state and a final cure state that are activated by the epoxy being heated to different temperatures for a period of time, respectively, by conduction, convention, and/or radiation. In another example, the bonding agent may be a bonding material that is activated to an initial bonding state and a final bonding state by being exposed to different doses and/or duration of ultraviolet radiation, respectively. In another example, the bonding agent may be a bonding material that is activated to an initial bonding state and a final bonding state by being exposed to different compounds or different amounts of the same compound, respectively. According to the process  4000 , the bonding agent may be bonded to the back surface  166  of the face portion  162  by being activated to the initial bonding state. A polymer material is then injected in the interior cavity  700  of the golf club head  100  (block  4020 ). The example process  4000  then includes bonding the polymer material to the bonding agent (block  4030 ). Bonding the polymer material to the bonding agent may include activating the bonding agent to the final bonding state to permanently bond the polymer material to the bonding agent and to permanently bond the bonding agent to the back surface  166  of the face portion  162 . The example process  4000  is merely provided and described in conjunction with other figures as an example of one way to manufacture the golf club head  100 . While a particular order of actions is illustrated in  FIG. 40 , these actions may be performed in other temporal sequences. Further, two or more actions depicted in  FIG. 40  may be performed sequentially, concurrently, or simultaneously. 
       FIG. 41  depicts one manner that the interior cavity  700  of the golf club head  100  or any of the golf club heads described herein may be partially or entirely filled with one or more filler materials such any of the filler materials described herein. The process  4100  may begin with applying a bonding agent (e.g., a bonding portion  1910  of  FIG. 19 ) to the back surface  166  of the face portion  162  of the golf club head  100  (block  4110 ). The bonding agent may be any type of adhesive and/or other suitable materials. In one example, the bonding agent may be an epoxy. Prior to applying the bonding agent, the golf club head  100  may be cleaned to remove any oils, other chemicals, debris or other unintended materials from the golf club head  100  (not shown). The bonding agent may be applied on the back surface  166  as described herein depending on the properties of the bonding agent. The bonding agent may be applied to the back surface  166  of the face portion  162  through one or more of the first set of ports  1420  and/or the second set of ports  1430 . For example, the bonding agent may be in liquid form and injected on the back surface  166  through several or all of the first set of ports  1420  and the second set of ports  1430 . An injection instrument (not shown) such as a nozzle or a needle may be inserted into each port until the tip or outlet of the injection instrument is near the back surface  166 . The bonding agent may then be injected on the back surface  166  from the outlet of the injection instrument. Additionally, the injection instrument may be moved, rotated, and/or swiveled while inside the interior cavity  700  so that the bonding agent may be injected onto an area of the back surface  166  surrounding the injection instrument. For example, the outlet of the injection instrument may be moved in a circular pattern while inside a port to inject the bonding agent in a corresponding circular pattern on the back surface  166 . Each of the first set of ports  1420  and the second set of ports  1430  may be utilized to inject a bonding agent on the back surface  166 . However, utilizing all of first ports  1420  and/or the second set of ports  1430  may not be necessary. For example, using every other adjacent port may be sufficient to inject a bonding agent on the entire back surface  166 . In another example, ports  1421 ,  1422   1431 ,  1433  and  1436  may be used to inject the bonding agent on the back surface  166 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The example process  4100  may also include spreading or overlaying the bonding agent on the back surface  166  (not shown) after injecting the bonding agent onto the back surface  166  so that a generally uniform coating of the bonding agent is provided on the back surface  166 . According to one example, the bonding agent may be spread on the back surface  166  by injecting air into the interior cavity  700  through one or more ports of the first set of ports  1420  and/or the second set of ports  1430 . The air may be injected into the interior cavity  700  and on the back surface  166  by inserting an air nozzle into one or more ports of the first set of ports  1420  and/or the second set of ports  1430 . According to one example, the air nozzle may be moved, rotated and/or swiveled at a certain distance from the back surface  166  to uniformly blow air onto the bonding agent and spread the bonding agent on the back surface  166  for a uniform coating or a substantially uniform coating of the bonding agent on the back surface  166 . Further, the golf club head  100  may be pivoted back and forth in one or several directions so that the bonding agent may spread along a portion or substantially the entire area of the back surface  166  of the face portion  162 . In one example, the golf club head  100  may be vibrated with the back surface  166  of the face portion  162  in a generally horizontal orientation so that the bonding agent may spread or overlay on the back surface  166  in a uniform coating manner or a substantially uniform coating manner. The apparatus, methods, and articles of manufacture are not limited in this regard. 
     The example process  4100  is merely provided and described in conjunction with other figures as an example of one way to manufacture the golf club head  100  or any of the golf club heads described herein. While a particular order of actions is illustrated in  FIG. 41 , these actions may be performed in other temporal sequences. Further, two or more actions depicted in  FIG. 41  may be performed sequentially, concurrently, or simultaneously. The example process  4100  may include a single action (not shown) of injecting and uniformly or substantially uniformly coating the back surface  166  with the bonding agent. In one example, the bonding agent may be injected on the back surface  166  by being converted into fine particles or droplets (i.e., atomized) and sprayed on the back surface  166 . Accordingly, the back surface  166  may be uniformly or substantially uniformly coated with the bonding agent in one action. A substantially uniform coating of the bonding agent on the back surface  166  may be defined as a coating having slight non-uniformities due to the injection process or the manufacturing process. However, such slight non-uniformities may not affect the bonding of the elastic polymer material or elastomer material to the back surface  166  with the bonding agent as described herein. For example, spraying the bonding agent on the back surface  166  may result in overlapping regions of the bonding agent having a slightly greater coating thickness than other regions of the bonding agent on the back surface  166 . The apparatus, methods, and articles of manufacture are not limited in this regard. 
     In one example as shown in  FIG. 42 , the bonding agent may be an epoxy having different curing states based on the temperature and the amount of time to which the epoxy may be exposed. The bonding agent may have an uncured state, an initial cure state, and a final cure state. In one example, the uncured state may be a liquid state, the initial cure state may be gel or a semi-solid/semi-liquid state, and the final cure state may be a solid state. The bonding agent may transition from the uncured state to the initial cure state when the bonding agent is heated to a temperature between an initial cure state temperature (Temp i ) and a final cure state temperature (Temp f ) for a period of time. Accordingly, an initial cure state temperature range may be defined by temperatures that are greater than or equal to the initial cure state temperature Temp i  and less than the final cure state temperature Temp f . The bonding agent may transition from the initial cure state to the final cure state when the bonding agent may be heated to a temperature greater than or equal to the final cure state temperature Temp f  for a period of time. Accordingly, a final cure state temperature range may be defined by temperatures that are greater than or equal to the final cure state temperature Temp f . The initial cure state temperature Temp i  and the final cure state temperature Temp f  may vary based on the amount of time that the bonding agent may be heated. In particular, a transition from the uncured state to the initial cure state and a transition from the initial cure state to the final cure state may be dictated by certain temperature and time profiles based on the properties of the bonding agent. At a temperature below the initial cure temperature Temp i , the bonding agent may be in the uncured state (e.g., a liquid state). In the initial cure state, the bonding agent may form an initial bond with an object and become pliable to be manipulated (e.g., moved, spread, overlay, etc.) without obtaining full cross linking or forming a permanent bond. In other words, the bonding agent may form an initial bond with an object and be manipulated without forming a permanent bond. In the final cure state, the bond of the bonding agent (e.g., cross linking for a bonding agent that includes epoxy) may be complete or become permanently set. 
     The bonding agent may be applied to the back surface  166  of the face portion  162  when the bonding agent is in the uncured state, which may be a liquid state. Subsequently, the golf club head  100  and/or the bonding agent may be heated to a first temperature Temp 1  that is greater than or equal to the initial cure state temperature Temp i  and less than the final cure state temperature Temp f  to change the bonding agent from an uncured state to an initial cure state (i.e., an initial cure state temperature range) (block  4120 ). Accordingly, the bonding agent may form an initial bond with the back surface  166  of the face portion  162 . After bonding the bonding agent to the back surface  166 , the golf club head  100  may be cooled for a period of time at ambient or room temperature (not shown). Accordingly, the bonding agent may be in an initial cured state and bonded to the back surface  166  of the face portion  162  so that the bonding agent may be bonded to the back surface  166  during the injection molding of a polymer material in the interior cavity  700 . Ambient or room temperature may be defined as a room temperature ranging between 5° C. (32° F.) and 31° C. (104° F.). The first temperature Temp 1  and duration by which the golf club head  100  and/or the bonding agent heated to the first temperature Temp 1  may depend on the curing or bonding properties of the bonding agent. The apparatus, methods, and articles of manufacture are not limited in this regard. 
     After the bonding agent is bonded to the back surface  166  of the face portion  162 , the golf club head  100  may be heated (i.e., pre-heating the golf club head  100 ) prior to receiving a polymer material (not shown). The golf club head  100  may be heated so that when the polymer material is injected in the golf club head  100 , the polymer material is not cooled by contact with the golf club head and remains in a flowing liquid form to fill the internal cavity  700 . The temperature at which the golf club head is heated, which may be referred to herein as a third temperature, may be similar to the temperature of the polymer material when being injected into the internal cavity  700 . However, the temperature at which the golf club head is heated may be less than the final cure temperature Temp f  of the bonding agent. Accordingly, the bonding agent may not transition from the initial cure state to the final cured state during the injection molding process. Further, the pre-heating temperature of the golf club head  100  may be determined so that excessive cooling of the golf club head  100  may not be necessary after injection molding the polymer material in the internal cavity  700 . Prior to being injected into the internal cavity  700 , the polymer material may also be heated to a liquid state (not shown). The temperature at which the polymer material may be heated may depend on the type of polymer material used to partially or fully fill the interior cavity  700 . Further, the temperature at which the polymer material is heated may be determined so that shrinkage of the polymer material is reduced during the injection molding process. However, as described herein, the polymer material may be heated to a temperature that is less than the final cure temperature Temp f  of the bonding agent. The apparatus, methods, and articles of manufacture are not limited in this regard. 
     As described herein, the cavity  700  may be partially or fully filled with a polymer material by injecting the polymer material in the cavity  700  (block  4130 ). The injection speed of the polymer material may be determined so that the interior cavity  700  may be slowly filled to provide a better fill while allowing air to escape the interior cavity  700  and allowing the injected polymer material to rapidly cool. For example, the polymer material may be a non-foaming and injection-moldable thermoplastic elastomer (TPE) material. The polymer material may be injected into the interior cavity  700  from one or more of the ports described herein (e.g., one or more ports of the first and second sets of ports  1420  and  1430 , respectively, shown in  FIG. 14 ). One or more other ports may allow the air inside the interior cavity  700  displaced by the polymer material to vent from the interior cavity  700 . In one example, the golf club head  100  may be oriented horizontally as shown in  FIG. 14  during the injection molding process. The polymer material may be injected into the interior cavity  700  from ports  1431  and  1432 . The ports  1421 ,  1422  and/or  1423  may serve as air ports for venting the displaced air from the interior cavity  700 . Thus, regardless of the orientation of the golf club head  100  during the injection molding process, the polymer material may be injected into the interior cavity  700  from one or more lower positioned ports while one or more upper positioned ports may serve as air vents. 
     According to one example, any one of the ports or any air vent of the golf club head  100  used as air port(s) for venting the displaced air may be connected to a vacuum source (not shown) during the injection molding process. Accordingly, air inside the interior cavity  700  and displaced by the polymer material may be removed from the interior cavity  700  by the vacuum source. Accordingly, trapped air pocket(s) in the interior cavity  700  and/or a non-uniform filling of the interior cavity  700  with the polymer material may be reduced. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     After injecting the polymer material into the interior cavity  700 , the golf club head  100  may be heated to a second temperature Temp 2  that is greater than or equal to the final cure temperature Temp f  of the bonding agent to reactivate the bonding agent to bond the polymer material to the bonding agent (i.e., a final cure state temperature range) (block  5040 ). The second temperature Temp 2  and the duration by which the golf club head  100  is heated to the second temperature Temp 2  may depend on the properties of the bonding agent as shown in  FIG. 42  to form a permanent bond between the golf club head  100  and the bonding agent and between the polymer material and the bonding agent. The golf club head  100  may be then cooled at ambient or room temperature (not shown). According to one example, the characteristic time (CT) of the golf club head  100  may be measured (not shown) after manufacturing the golf club head  100  as described herein. CT measurements may determine if the golf club head  100  conforms to CT rules established by one or more golf governing bodies. 
     The heating and cooling processes described herein may be performed by conduction, convention, and/or radiation. For example, all of the heating and cooling processes may be performed by using heating or cooling systems that employ conveyor belts that move the golf club head  100  through a heating or cooling environment for a period of time as described herein. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     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. 
     While the above examples may described 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. 
     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 “and” and “or” may have both conjunctive and disjunctive meanings. The terms “a” and “an” are defined as one or more unless this disclosure indicates otherwise. 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 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. 
     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. 
     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.