Patent Publication Number: US-2022226703-A1

Title: Golf club head having deflection features and related methods

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 16/888,496 filed May 29, 2020, which is a continuation of U.S. patent application Ser. No. 15/899,261 filed Feb. 19, 2018, now U.S. Pat. No. 10,668,338 issued Jun. 2, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/460,505, filed on Feb. 17, 2017. Further, this is a continuation in part of U.S. patent application Ser. No. 15/479,049, filed on Apr. 4, 2017, now U.S. Pat. No. 10,022,601 issued Jul. 17, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62/407,736, filed on Oct. 13, 2016, and U.S. Provisional Patent Application No. 62/318,017 filed on Apr. 4, 2016. Further still, this is a continuation in part of U.S. patent application Ser. No. 14/710,236, filed on May 12, 2015, which claims the benefit of U.S. Provisional Patent Application No. 62/146,783 filed on Apr. 13, 2015, U.S. Provisional Patent Application No. 62/101,926 filed on Jan. 9, 2015, U.S. Provisional Patent Application No. 62/023,819 filed on Jul. 11, 2014, and U.S. Provisional Patent Application No. 61/994,029, filed on May 15, 2014. Further still, this claims the benefit of U.S. patent application Ser. No. 15/470,369, filed on Mar. 27, 2017, which claims the benefit of U.S. Provisional Patent Application No. 62/313,214, filed on Mar. 25, 2016. The contents of all of the above-described applications are incorporated fully herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to a golf club head including multiple features to optimize ball speed and launch distance, while not compromising the acoustics produced by the golf club head after the point of impact. 
     BACKGROUND 
     A golfer benefits from having a club that provides high ball speed and greater carry distance. Many golf club characteristics are considered when designing a golf club head to achieve desired performance characteristics, such as distribution of mass, energy transferred to the ball from the face, along with the acoustics produced by the club head after impact. 
     Various iron-type golf club heads include a void positioned behind the face, and a weight or insert positioned in the void to provide desired weighting characteristics to the club head. The weight or insert generally contacts the back side of the face, thereby damping vibrations at impact to create a desirable sound after impact with a golf ball. The insert placed in contact with the face also leaches energy from the impact, energy that is prevented from being transferred back into the golf ball to increase the ball speed after impact. There is a need in the art for a golf club head that produces desirable acoustics and proper swingweighting, while also transferring a maximum amount of energy back into the golf ball after the point of impact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a golf club head having a deflection feature according to one embodiment. 
         FIG. 2  is a back view of the golf club head of  FIG. 1 . 
         FIG. 3  is a toe side cross-sectional view of the golf club head of  FIG. 1 . 
         FIG. 4  is a perspective view of an insert according to one embodiment. 
         FIG. 5  is a toe side cross-sectional view of a golf club head comprising the insert of  FIG. 4 . 
         FIG. 6  is a perspective view of an insert according to another embodiment. 
         FIG. 7  is a top view of the insert of  FIG. 6 . 
         FIG. 8  is a side view of the insert from  FIG. 6 . 
         FIG. 9  is a side view of an insert according to another embodiment. 
         FIG. 10  is a cross-sectional side view of an insert according to another embodiment. 
         FIG. 11  is a cross-sectional front view of the insert from  FIG. 10 . 
         FIG. 12  is a perspective view of an insert according to another insert. 
         FIG. 13  is a cross-sectional view of a golf club head comprising the insert from  FIG. 10 . 
         FIG. 14  is a cross-sectional view of a golf club head comprising the insert from  FIG. 12 . 
         FIG. 15  is a cross-sectional view of a golf club head comprising the insert from  FIG. 9 . 
         FIG. 16  is a cross-sectional view of a golf club head having a thin uniform sole. 
         FIG. 17  is a cross-sectional view of a golf club head having a cutout in the top rail. 
         FIG. 18  is a front view of a multi-material weight. 
         FIG. 19  is a cross-sectional view of a golf club head comprising the multi-material weight of  FIG. 18 . 
         FIG. 20  is a rear perspective view of a golf club head having a reinforcement device. 
         FIG. 21  is a front perspective view of the golf club head of  FIG. 20 . 
         FIG. 22  is a front view of a conventional club head, according to an embodiment. 
         FIG. 23  is a stress-strain analysis of a partial cross-sectional view of the conventional club head taken along section line  4 - 4  of  FIG. 22  simulating a face surface of the conventional club head impacting a golf ball (not shown), where the resulting bending is multiplied three-fold, according to the embodiment of  FIG. 22 . 
         FIG. 24  is a cross-sectional view of the club head taken along section line  5 - 5  of  FIG. 21 , according to the embodiment of  FIG. 20 . 
         FIG. 25  is a rear perspective view of a golf club head having a reinforcement device according to a different embodiment. 
         FIG. 26  is a side cross-sectional view of the club head taken along section line  5 - 5  of  FIG. 21 , according to a different embodiment of  FIG. 20 . 
         FIG. 27  is a top, rear, heel side view of a club head, according to the embodiment of  FIG. 26 . 
         FIG. 28  is a side view of the club head taken along section line  5 - 5  of  FIG. 21 , according to the embodiment of  FIG. 20 . 
         FIG. 29A  is a perspective side cross-sectional view of a stress simulation of a control club head having a reinforcement device devoid of a fillet during impact with a golf ball. 
         FIG. 29B  is a side cross-sectional view of a stress simulation of a control club head having a reinforcement device devoid of a fillet during impact with a golf ball. 
         FIG. 30A  is a perspective side cross-sectional view of a stress simulation of an exemplary golf club head having a reinforcement device with a fillet during impact with a golf ball. 
         FIG. 30B  is a side cross-sectional view of a stress simulation of an exemplary golf club head having a reinforcement device with a fillet during impact with a golf ball. 
         FIG. 31A  is a perspective side cross-sectional view of a stress simulation of a control golf club head having a reinforcement device with large rib span during impact with a golf ball. 
         FIG. 31B  is a side cross-sectional view of the club head of  FIG. 31A . 
         FIG. 31C  is a rear perspective view of the club head of  FIG. 31A . 
         FIG. 32A  is a perspective side cross-sectional view of a stress simulation of a control golf club head having a reinforcement device with small rib span during impact with a golf ball. 
         FIG. 32B  is a side cross-sectional view of the club head of  FIG. 32A . 
         FIG. 32C  is a rear perspective view of the club head of  FIG. 32A . 
         FIG. 33A  is a perspective side cross-sectional view of a stress simulation of an exemplary golf club head having a reinforcement device with rib span according to the disclosure during impact with a golf ball. 
         FIG. 33B  is a side cross-sectional view of the club head of  FIG. 33A . 
         FIG. 33C  is a rear perspective view of the club head of  FIG. 33A . 
     
    
    
     DETAILED DESCRIPTION 
     Described herein is an iron-type golf club head having various features to increase ball speed and ball launch distance, while producing desirable acoustics, optimized mass distribution, and maintaining a small body size (i.e. a compact distance iron). Specifically, the compact distance iron can include a face comprising an optimized material, a rear cavity positioned behind the face, an insert positioned behind the face, a reinforcement device, a thinned uniform sole, and a top rail comprising a cutout,. Additionally, the golf club head can be formed as a single unibody cast, significantly reducing the cost of manufacturing. 
     The insert can comprise specific geometries, which allow the insert to positively damp vibrations in the club head, manipulate the mass distribution for proper swing weighting, while still allowing the face to deflect and transfer a maximum amount of energy back to the golf ball at impact. The insert can contact the rear surface of the face at certain locations and be spaced a predetermined distance from the face in areas which the ball is most likely to contact the face. In other embodiments, an entire surface of the insert can contact the rear surface of the face. The insert can also include voids, which allow the face to deform without absorbing energy from the impact, while damping vibrations at impact to generate the desired acoustics. Different geometries of voids can be used to adjust the face deflection on impact, swing weighting, and/or the sound emitted by the golf club at impact. Further, the voids can ensure the face of the golf club head is able to deflect, while minimizing energy loss to the insert. Therefore, the face is able to maximize the amount of energy transferred back to the golf ball after impact, resulting in increased ball speeds and greater launch distances. 
     In some embodiments, the insert can comprise a reinforcement device that can transfer stress away from the face and into the reinforcement device to support a thin face. The thin face can deflect more on impact with a golf ball (compared to a typical thicker face), thereby increasing energy transfer back to the ball on impact, resulting in increased ball speed and travel distance. 
     In many embodiments, the reinforcement device can comprise a face surface nearer to the rear surface proximal to the face center than proximal to the face perimeter, an outer perimeter surface that is filleted with the rear surface, an inner surface comprising a largest rib span of greater than or equal to approximately 0.609 centimeter to approximately 1.88 centimeters, and/or a face element that is thinner within the inner perimeter surface that without or outside the outer perimeter surface. 
     The club head having the reinforcement device with one or more of the aforementioned features experiences increased ball speed and travel distance, while maintaining club head durability compared to a club head devoid of the reinforcement device. The disclosed club head having a reinforcement element and fillet allows the center face plat thickness to be reduced without increasing (in fact, while reducing) the stress on the faceplate, due to the unique stress transfer properties of the described structure. The reduced center thickness of the club head having the reinforcement device further allows increased bending on impact with a golf ball, without sacrificing durability, thereby increasing ball speed and travel distance. 
     In many embodiments, the golf club head is an iron type golf club head. In other embodiments, the golf club head can be any type of golf club head. For example, the club head can be a driver, a fairway wood, a hybrid, a one-iron, a two-iron, a three-iron, a four-iron, a five-iron, a six-iron, a seven-iron, an eight-iron, a nine-iron, a pitching wedge, a gap wedge, a utility wedge, a sand wedge, a lob wedge, and/or a putter. 
     In addition, the golf club head can have a loft that can range from approximately 3 degrees to approximately 75 degrees. For example, the golf club head can have a loft of 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, 25, 25.5, 26, 26.5, 27, 27.5, 28, 28.5, 29, 29.5, 30, 30.5, 31, 31.5, 32, 32.5 ,33, 33.5, 34, 34.5, 35, 35.5, 36, 36.5, 37, 37.5, 38, 38.5, 39, 39.5, 40, 40.5, 41, 41.5, 42, 42.5, 43, 43.5, 44, 44.5, 45, 45.5, 46, 46.5, 47, 47.5, 48, 48.5, 49, 49.5, 50, 50.5, 51, 51.5, 52, 52.5, 53, 53.5, 54, 54.5, 55, 55.5, 56, 56.5, 57, 57.5, 58, 58.5, 59, 59.5, 60, 60.5, 61. 61.5, 62, 62.5, 63, 63.5, 64, 64.5, 65, 65.5, 66, 66.5, 67, 67.5, 68, 68.5, 69, 69.5, 70, 70.5, 71, 71.5, 72, 72.5, 73, 73.5, 74, 74.5, and/or 75 degrees). In many embodiments, the club head can have a loft greater than or equal to 15 degrees, greater than or equal to 20 degrees, greater than or equal to 25 degrees, greater than or equal to 30 degrees, greater than or equal to 45 degrees, greater than or equal to 50 degrees, or greater than or equal to 55 degrees. 
     The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include,” and “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but can include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus. 
     The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the apparatus, methods, and/or articles of manufacture described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. 
     Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. 
       FIGS. 1 and 2  illustrate a golf club head  10  comprising a body  12  having a toe end  14  opposite a heel end  16 , a top rail  18  opposite the sole  20 , and a face  22  opposite a rear end  24 . A plurality of grooves  26  can be positioned on the face  22 . The golf club head  10  can also include a hosel  28  configured to receive a golf club shaft (not shown) that can include a grip (not shown). 
     Referring now to  FIG. 3 , the golf club head  10  comprises a cavity  30  that is formed between the face  22  and the rear end  24 . More specifically, the cavity  30  is partially formed by an interior wall  32  of the rear end  24 , by a sole interior surface  34 , and by a face interior surface  36 . During impact with a golf ball the face  22  deflects towards the rear end  24  of the golf club head  10  and then springs forward imparting energy into the golf ball (not shown) upon impact. 
     The golf club head  10  can further include at least one deflection feature. The deflection feature can be an insert positioned in the cavity  30 . The golf club head  10  can further include one or more features selected from the group consisting of a thin uniform sole  20 , one or more optimized face  22  materials, a cutout in the top rail  18  of the golf club head  10 , a thin face, and a reinforcement device  1112 . The golf club head  10  can comprise one of or any combination of the aforementioned features. The weight savings produced by the aforementioned deflection features allow the golf club head  10  to further comprise a dual density weight. In some embodiments, the weight can be added to move the club head center of gravity low and back, while increasing club head moment of inertia. Further, the golf club head  10  comprising the aforementioned features can be a single cast unibody reducing the manufacturing costs. 
     I) Deflection Feature Comprising an Insert 
     As discussed above, the deflection feature of the golf club head  10  can comprise an insert (e.g.  50 ,  150 ,  250 ,  350 ,  450 , as described below). In some embodiments, the insert can be positioned within the cavity  30 . The insert can provide multiple benefits to the golf club head  10 . First, the insert can aid in swing weighting the golf club head  10 . Second, the insert can damp unwanted vibrations within the club head  10  to adjust the acoustics of the golf club head  10 . Third, the insert can provide the aforementioned benefits without inhibiting deflection of the face  22 , thereby minimizing the absorption of energy from the face deflection during impact to increase energy transfer to the golf ball, increase ball speed and carry distance, and damp vibrations. 
     The insert has a spring constant defined by Hooke&#39;s law. An insert having a low spring constant requires less force to deform the insert. Therefore, an insert with a low spring constant will deform more on impact with a golf ball, beneficially preventing unneeded absorption of energy from the impact, and enabling deformation of the face  22 . The spring constant, k, can be determined using Hooke&#39;s Law in relation 1 below, where X represents the distance of compression due to a force, F: 
     
       
         
           
             
               
                 
                   k 
                   = 
                   
                     F 
                     X 
                   
                 
               
               
                 
                   Relation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     Both the geometry and the material of the insert can affect the spring constant. Generally, a material having a higher density has a greater spring constant. The insert can comprise one or more materials, including, but not limited to, steel, tungsten, aluminum, titanium, metal alloys, other metals, composites, polymers, plastic, plastics with powdered metals, elastomers, elastomers with powdered metals, and/or any combination thereof. In some embodiments, the insert can be made of the same material(s) or can be made of material(s) different than the golf club head  10 . In some embodiments, the insert can comprise two separate materials. The portion of the insert contacting the face can be a low density material having a low spring constant, while the rear portion of the insert can be a higher density material, functioning as a swing weight. 
     In addition, in many embodiments, the insert can be formed separately and inserted into the cavity  30  after manufacturing of the golf club head  10 . In other embodiments, the insert can be formed in the cavity  30  during manufacturing of the golf club head  10  (e.g., during casting, forging, etc.). In these embodiments, the insert can be integrally formed as a unitary construction with the remainder of the golf club head  10 . 
     The insert can comprise various geometries, as described in further detail below. In some embodiments, a gap is positioned between the face  22  and the insert. Placing a gap between the face  22  and the insert results in no energy being absorbed by the insert on impact with a golf ball. In other embodiments, the insert can comprise a plurality of voids. The plurality of voids can be positioned across the entire insert or in the portion of the insert contacting the face  22 . The voids decrease the compression of the insert on impact with a golf ball, which lowers the spring constant, compared to an insert without voids.
     a. Deflection Feature Comprising Insert with a Gap   

     As discussed above, the deflection feature of the golf club head  10  can be an insert positioned such that a gap exists between the face  22  and the insert. Referring to  FIG. 4 , an embodiment of the insert  50  is displayed. The insert  50  comprises a front surface having a first surface  51  that is positioned adjacent to and offset from a second surface  52 . A step  40  defines the transition between the first surface  51  and the second surface  52  of the insert  50 . In the illustrated embodiment, the first surface  51  comprises a cross member  53  and two arm members  54 , which form a “U” shaped protrusion extending outward from the second surface  52 . The first surface  51  is protruded from the second surface  52  such that when positioned in the cavity  30  of the golf club head  10 , the first surface  51  is in contact with the face interior surface  36 , and the second surface  52  is spaced from the face interior surface  36 . The insert  50  also includes a bottom surface  55  that is configured to contact the sole interior surface  34  of the cavity  30 , a top surface  56  that is opposite the bottom surface  55 , and a back surface  57  that is configured to contact the rear end interior surface  32 . In other embodiments, the cross member  53  and two arm members  54 , which form the first surface  51  can form any shape protruding from the second surface  52 . For example, in some embodiments, the first surface  51  can form a triangular, circular, oval, rectangular, polygonal or any other suitable protruded shape extending from the second surface  52 . 
       FIG. 5  illustrates the insert  50  in relation to the golf club head  100 . The golf club head  100  is similar to golf club head  10 , except golf club head  100  comprises insert  50 . In the illustrated embodiment, the first surface  51  and second surface  52  of the insert  50  are positioned adjacent to the face interior surface  136 . The first surface  51  contacts the outer perimeter of the face interior surface  136 . The second surface  52  is offset from the first surface  51  by the step  40  and creates a gap  41  with the face interior surface  136 . In the illustrated embodiment, the second surface  52  is tapered away from the face interior surface  136  at a tapering angle defined between the second surface  52  and the face interior surface  136 . In some embodiments, the second surface  52  can have a tapering angle of greater than 0°, and more preferably can range from approximately 0.01° to approximately 20°, and more preferably can range from approximately 0.10° to approximately 15°, and more preferably can range from approximately 0.10° to approximately 10°, and more preferably can range from approximately 0.10° to approximately 5°, and more preferably can range from approximately 0.10° to approximately 2°, and more preferably can range from approximately 0.10° to approximately 1.5°, and more preferably can be at or less than approximately 10°, and more preferably can be at or less than approximately 7.5°, and more preferably can be at or less than approximately 5°, and more preferably can be at or less than approximately 3°, and more preferably can be at or less than approximately 2°, and more preferably can be at or less than approximately 1°. In other words, the gap  41  width, measured perpendicular from the face interior surface  136  to the second surface  52 , increases from near the bottom surface  55  to the top surface  56 . In other embodiments, the gap  41  width can decrease from near the bottom surface  55  to the top surface  56 . Further, in other embodiments, the gap width can be greatest near the center of the face and can decrease radially toward the bottom surface  55 , toward to toe end, and toward the heel end. In other embodiments, the second surface  52  can be parallel with the face interior surface  136  and therefore, the gap  41  width can remain constant from near the bottom surface  55  to the top surface  56 . Further, the gap  41  width can increase, decrease or remain constant across the length (heel to toe) of the golf club head  100 . 
     The gap  41  width can range from approximately 0.001 inches to approximately 0.125 inches, and more preferably can range from approximately 0.005 inches to approximately 0.125 inches, and more preferably can range from approximately 0.005 inches to approximately 0.075 inches, and more preferably can range from approximately 0.005 inches to approximately 0.050 inches. In addition, the maximum width of the gap  41  can exceed approximately 0.005 inches, and more preferably can exceed approximately 0.020 inches, and more preferably can exceed approximately 0.050 inches, and more preferably can exceed approximately 0.075 inches, and more preferably can be up to approximately 0.125 inches. The gap  41  can comprise 10-60% of the front surface of the insert  50 . For example, in some embodiments, the gap  41  can comprise 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60% of the front surface of the insert  50 . 
     During impact with a golf ball, the face  122  of the club head  100  having the insert  50  undergoes deformation or deflection. The face plate  122  deforms or deflects in a direction generally towards the rear end  124 . The face plate  122  has the greatest deformation near the center of the face  122 , wherein the gap  41  exists. In many embodiments, the width of the gap  41  is large enough that the face  122  never contacts the second surface  52  of the insert  50 . The gap  41  is occupied by air and as such, has a spring constant of zero and does not inhibit deflection of the face  122 . Therefore, the second surface  52  of the insert  50  does not absorb any energy from the impact with the golf ball and the face  122  is able to rebound transferring a majority of the energy from impact back to the golf ball. The first surface  51  of the insert  50  is positioned around the lower perimeter of the face interior surface  136 , wherein the face  122  does not deflect. As such, the first surface  51  is able to damp vibrations caused by the impact, without inhibiting face  122  deflection or absorbing large amounts of energy. The result is a golf club head  100  comprising an insert  50 , wherein the insert  50  damps vibration to achieve desired impact acoustics, while not inhibiting face  122  deflection. Further, the gap  41  positioned near the first and top surfaces  51 ,  56  of the insert  50 , results in the insert  50  having a majority of its mass positioned towards its second and bottom surfaces  52 ,  55 . Therefore, the insert  50  can also be utilized as a swing weight to move the CG of the golf club head  100  low and back, improving the MOI. 
     In other embodiments, the width of the gap  41  is less than the total deformation of the face  122 . In these or other embodiments, during impact, the face  122  continues to deform or deflect until a portion of the gap  41 , or the entirety of the gap  41 , collapses. For example, at impact, the face  122  deforms or deflects until the face interior surface  136  impacts (or comes into contact with) the insert  50 , and more specifically impacts the second surface  52  of the insert  50 . In other embodiments, a portion of the gap  41  can partially or completely collapse. In yet other embodiments, a first portion of the gap  41  can partially collapse, while a second portion of the gap  41  can completely collapse. The amount and/or location of gap  41  collapse can depend on various factors, including, but not limited to, the golf ball impact location on the face  122  (e.g., towards the toe  114 , towards the heel  116 , towards the top rail  118 , towards the sole  120 , at the “sweet spot,” etc.), the swing speed of the golfer, etc. 
     Once the gap  41  has collapsed, the insert  50  can partially deform to further increase deformation or deflection of the face  122 . Once the insert  50  can no longer deform, deformation of the face  122  ceases. The amount the insert  50  is able to deform directly correlates with the spring constant of the insert  50 . Therefore, as discussed above, the maximum amount of deformation can be adjusted by changing the material or geometry of the insert  50 . Once the gap  41  has collapsed, the insert  50  can support the face plate  122  from further deformation or deflection to reduce the risk of reaching irreversible plastic deformation. The face  122  and insert  50  then rebound to their respective pre-impact positions (i.e., the gap  41  reforms), generating a desired spring-like effect that results in an increased golf ball speed and an increased golf ball travel distance.
     b. Deflection Feature Comprising Insert with Voids   

       FIGS. 6-15  illustrate various embodiments of an insert having a plurality of voids. The inserts of  FIGS. 6-15  are similar to insert  50 , except the inserts of  FIGS. 6-15  can be devoid of a gap. The inserts of  FIGS. 6-15  comprise a front surface opposite a rear surface, a top surface opposite a bottom surface, and a toe end opposite the heel end. Further, inserts of  FIGS. 6-15  can comprise a plurality of voids. The plurality of voids can function similarly to the gap  41  of insert  50 . Specifically, the plurality of voids can lower the spring constant or effective elastic modulus of the insert, allowing the insert  150  to deform such that it does not inhibit, or minimally inhibits, the deformation of the face at impact. Increasing the deformation of the insert, as a result of the voids, allows the face  22  to deflect more and transfer more energy back to a golf ball on impact, thereby increasing ball speed and travel distance, compared to a club head having a solid insert without voids. 
     The insert having a plurality of voids comprises a void ratio defined as a ratio between the volume of voided space to the volume of solid space within the insert. Increasing the volume of voids within the insert increases the void ratio and lowers the spring constant or effective elastic modulus of the insert. In many embodiments, the insert with a plurality of voids can comprise a void ratio up to 0.20, up to 0.30, up to 0.40, up to 0.50, up to 0.60, up to 0.70, up to 0.80, or up to 0.90. In other embodiments, the insert can comprise a void ratio between 0.05 and 0.80, between 0.10 and 0.60, between 0.05 and 0.60, or between 0.10 and 0.60. 
     Referring to  FIGS. 6 and 7 , an embodiment of an insert  150  having a plurality of voids is illustrated. In the illustrated embodiment, the plurality of voids  160  extend in a direction from the top surface  153  to the bottom surface  154  of the insert  150 . 
     Referring to  FIG. 7 , each void  160  of the plurality of voids  160  has a circular cross section, which extends through the entirety of the insert  150  (from the top surface  153  to the bottom surface  154 ). The voids  160  are placed in a uniform pattern, wherein each void  160  is spaced uniformly from each void  160  adjacent to it. The voids  160  can be grouped into rows extending from the toe end  155  to the heel end  156  of the insert  150 . The insert  150  can comprise multiple rows extending from near the front surface  151  to near the rear surface  152 . In some embodiments, each row can have a uniform spacing from the row before and/or after it. In other embodiments, the distance between each row can increase, decrease or remain constant from front surface  151  to the rear surface  152  of the insert  150 . In other embodiments, the distance between a row of voids  160  and an adjacent row of voids  160  can vary from the toe end  155  to the heel end  156 . For example, the spacing between the rows of voids  160  near the toe and heel end  155 ,  156  can be greater or less than near the center of the insert  150 . In other embodiments, the spacing between the rows of voids  160  can be greater or less near the toe end  156  of the insert  150  than near the heel end  155  of the insert  150 . Further, in the illustrated embodiment, each row is offset from the row adjacent to it. In other embodiments, the rows can be positioned in any orientation with respect to the adjacent rows. 
     Referring again to  FIGS. 6 and 7 , in the illustrated embodiment, each void  160  is spaced a uniform distance from adjacent voids  160  within the same row. In other embodiments, the distance between adjacent voids  160  within the same row can increase, decrease or remain constant from the toe end  155  to the heel end  156 . In some embodiments, the distance between adjacent voids  160  within the same row can be between 0.005 to 0.5 inches. In other embodiments, each void  160  within the same row can be spaced apart by a distance within the range of 0.005 to 0.01, 0.01 to 0.05, 0.05 to 0.1, 0.1 to 0.15, 0.15 to 0.2, 0.2 to 0.25, 0.25 to 0.3, 0.3 to 0.35, 0.35 to 0.4, 0.4 to 0.45, or 0.45 to 0.5 inches. 
     Referring again to  FIGS. 6 and 7 , in the illustrated embodiment, each void  160  of the plurality of voids  160  has the same size and shape. In some embodiments, the size of the voids  160  can increase, decrease or remain constant from the toe end  155  to the heel end  156  of the insert  150 . For example, in some embodiments, the size of the voids  160  can be greatest in the center of the insert  150 , and can decrease in a direction toward the toe end  155  and the heel end  156  of the insert  150 . In other embodiments, the size of the voids  160  can increase, decrease or remain constant from the front surface  151  to the rear surface  152  of the insert  150 . For example, the size of the voids  160  can be greatest near the front surface  151  and decrease in a direction toward the rear surface  152  of the insert  150 . 
     The voids  160  can comprise any shape. For example, the voids  160  can have a triangular, rectangular, polygonal or any other suitable shape cross-section. In some embodiments, the insert  150  can comprise a plurality of voids  160  having two different cross sections. For example, the voids  160  near the front surface  151  of the insert can have a circular cross-section and the voids  160  near the rear surface  152  can have a triangular cross-section. In other embodiments, the insert  150  can comprise a plurality of voids  160  having up to 6 different cross-sectional shapes, positioned in any pattern on the insert  150 . 
     In some embodiments, the insert  150  (the volume defined between the front surface  151 , rear surface  152 , top surface  153 , bottom surface  154 , toe end  155 , and heel end  156 ) can comprise 50% voids  160 . In other embodiments, the insert can comprise between 5% and 80% voids. For example, in some embodiments, the insert 150 can comprise 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, 47.5%, 50%, 52.5%, 55%, 57.5%, 60%, 62.5%, 65%, 67.5%, 70%, 72.5%, 75%, 77.5%, or 80% voids  160 . 
     Having a higher concentration of voids  160  within the insert  150  lowers the spring constant or effective elastic modulus of the insert on impact with a golf ball, resulting in less energy being absorbed by the insert  150  at impact. However, a higher concentration of voids  160  within the insert  150  also removes weight from the insert  150  and can affect how the insert  150  functions as a swing weight. Generally, it is beneficial to have a greater portion of the mass distributed towards the sole and rear end of the golf club head. Therefore, in some embodiments, referring to  FIG. 8 , the insert  150  can have a high concentration of voids  160  in a first portion  157  towards the front surface  151  of the insert  150 , and have a low concentration of voids  160  in a second portion  158  towards the rear surface  152  of the insert  150 . As such, the first portion  157  of the insert  150  near the face of the golf club head has a low spring constant and will not inhibit deflection of the face, while the second portion  158  of the insert  150  near the rear end of the club head can have a higher mass to function as a swing weight. In the illustrated embodiment, the first portion  157  comprising the higher concentration of voids  160  is larger near the top surface  153  and tapers towards the front surface  151  as it extends towards the bottom surface  154  of the insert  150 . In other embodiments, the first portion  157  can increase or remain the same as it extends towards the bottom surface  154  of the insert  150 . 
     In some embodiments, the first portion  157  can comprise 50% percent of the insert  150 . In other embodiments, the first portion  157  can comprise at least 15% of the insert  150 . For example, the first portion  157  can comprise greater 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75% of the insert 150. Further, the first portion  157  can comprise greater than 10% voids  160 , while the second portion can comprise less that 75% voids  160 . For example, the first portion  157  of the insert  150  can comprise greater than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75% voids  160 , while the second portion  158  of the insert  150  can comprise less than 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, or 10% voids  160 . 
     In some embodiments, the first portion  157  can comprise the same material as the second portion  158 . In other embodiments, the first portion  157  can comprise a different material than the second portion  158 . For example, in some embodiments, the first portion  157  can comprise a material having a lower density resulting in a lower spring constant, while the second portion  158  can comprise a material having a higher density to better function as a swing weight. In other embodiments, the insert  150  can comprise up to 4 different portions, comprising different concentrations of voids  160  or materials. 
     Referring to  FIGS. 9 and 15 , another embodiment of an insert  250  is displayed. The insert  250  is similar to the insert  150  and can comprise the same variations as described above, except the voids  260  of insert  250  extend inward from the front surface  251  of the insert  250  toward the bottom surface of the insert  250 . Further, the voids  260  form a void angle  262 , defined between the bottom edge of the void  260  and the front surface  251  of the insert  250 . In the illustrated embodiment, the voids  260  form an acute void angle  262 . In other embodiments, the voids  260  can extent from the front surface toward the back surface or toward the top surface of the insert  250 . Further, in some embodiments, the void angle  262  can be obtuse angle or can be 90 degrees with the front surface  251 . Further, as mentioned above, the voids  260  can vary in size, shape, concentration, position and/or any other parameter described above in relation to voids  160 . 
     In some embodiments, each void  260  of  FIGS. 9 and 15  can extend from the heel end to the toe end of the insert  250 . In other embodiments, multiple voids  260  having any cross sectional geometry can positioned between the heel end and toe end of the insert. 
     Referring to  FIG. 15 , insert  250  comprising voids  260  is shown in relation to golf club head  200 . The club head  200  is similar to club head  10  and  100 , except it comprises insert  250  having a plurality of voids  260  as the deflection feature. The front surface  251  of the insert  250  is positioned adjacent to the face interior surface  236  of the cavity  230 . The rear surface  252  of the insert  250  is positioned adjacent to the rear end interior surface  232  of the cavity  230 . The bottom surface  254  of the insert  250  is positioned adjacent to the sole interior surface  234  of the cavity  230 . 
     In the illustrated embodiment, the voids  260  contact or extend to the face interior surface  236  of the golf club head  200 . The voids  260  are positioned at a void angle  262  (defined above), such that, at impact, the face  222  deflects, causing portions of the insert  250  on either side of the void  260  to deflect inward, collapsing the voids  260 . In many embodiments, the concentration of voids  260  contacting the face interior surface  236  is large enough that the spring constant of the insert  250  is substantially zero or is negligible. Therefore, the insert  250  absorbs minimal amounts of energy from the impact with the golf ball, and the face  222  is able to deflect and rebound fully, resulting in the face  222  transferring a majority of the energy from impact back to the golf ball. 
     For example, in some embodiments, the percentage of surface area of the front surface of the insert  250  comprising voids  260  can be between 5% and 80%. In other embodiments, the percentage of surface area of the front surface of the insert  250  comprising voids  260  can be 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, 47.5%, 50%, 52.5%, 55%, 57.5%, 60%, 62.5%, 65%, 67.5%, 70%, 72.5%, 75%, 77.5%, or 80%. 
     In embodiments where the concentration of voids  260  contacting or extending to the front surface of the insert against the face interior surface  236  is lower, the insert  250  can compress and absorb some energy from impact and then release the energy back into the face  222  by a spring back force. For example, the portion of the insert  250  on either side of the voids  260  can deflect at impact until the spring constant is too great for the force of impact to further deflect the insert  250 . At this point, the face  222  and the insert  250  will cease to deflect rearward, however, the energy from impact will be stored in the portions of the insert  250 , which were deflected. The insert  250  can then rebound back to its original position redistributing the energy to the face  222 . 
     Referring to  FIG. 10 , another embodiment of an insert  350  is shown. The insert  350  is similar to inserts  150  and  250  and can comprise the same variations as described above, except the voids  360  do not have a constant cross-section. The insert  350  can comprise a greater concentration of voids  360  near the top surface  353  than near the bottom surface  354 . In the illustrated embodiment, the voids  360  comprise a conic shape, wherein the cross-section has a circular shape across the entire length (extending in a direction from the top surface  153  to bottom surface  154 ) of the void  360 . However, the diameter of the circular cross-section decreases as the void  360  extends from the top surface  353  to the bottom surface  354 . Referring to  FIG. 11 , this creates an insert  350  having a higher concentration of voided area  381  (area comprising only air) near the top surface  353  than near the bottom surface  354  of the insert  350 . The voids  360  have gradually tapered edges, wherein the void  360  terminates prior to the bottom surface  354 . In some embodiments, the voids  360  can have cross-sections (not shown), which have abrupt steps from one diameter to the next. Further, in some embodiments, the voids  360  can have a concentration that decreases from the top surface  353  to the bottom surface  354 , but still extends through the bottom surface of the insert  354 . 
       FIG. 13  illustrates the insert  350  having a plurality of voids  360  in relation to a golf club head  300 . The golf club head  300  is similar to the golf club heads  10 ,  100  and  200 , except it comprises insert  350  having a plurality of voids  360  as the deflection feature. The front surface  351  of the insert  350  is positioned adjacent to the face interior surface  336  of the cavity  330 . The rear surface  352  of the insert  350  is positioned adjacent to the rear end interior surface  332  of the cavity  330 . The bottom surface  354  of the insert  350  is positioned adjacent to the sole interior surface  334  of the cavity  330 . 
     During impact with a golf ball, the face  322  of the club head  300  having the insert  350  undergoes deformation or deflection. The face plate  322  deforms or deflects in a direction generally towards the rear end  324 . The face plate  322  has the greatest deformation near the center of the face  322 , wherein the highest concentration of voided area exists. At impact, the voids  360  within the insert  350  collapse, allowing the face  322  to deflect with minimal to no inhibition from the insert  350 . In the illustrated embodiment, the insert  350  comprises conic shaped voids  360 , which are largest near the top surface  330  and which decrease as they extend towards the bottom surface  354 . The top surface  353  of the insert  350  is positioned adjacent to the center of the face  322 , which exhibits the greatest deflection on impact with a golf ball. As such, the portion of the insert  350  near the top surface  353  has a higher concentration of voids  360  maintain the maximum face  322  deflection. In many embodiments, the percentage of voided area in the portion of the insert  350  near the center of the face  322  is large enough that the spring constant of the insert  350  is essentially zero. As such, the insert  350  absorbs minimal amounts of energy from the impact with the golf ball, and the face  322  is able to deflect and rebound fully, resulting in the face  322  transferring a majority of the energy from impact back to the golf ball. For example, in some embodiments, the percentage of voided area (volume of voids  360  compared to volume of insert  350  material) in the portion of the insert  350  near the center of the face  322  can be between 5% and 80%. In other embodiments, the percentage of voided area in the portion of the insert  350  near the center of the face  322  can be 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, 47.5%, 50%, 52.5%, 55%, 57.5%, 60%, 62.5%, 65%, 67.5%, 70%, 72.5%, 75%, 77.5%, or 80%. In these or other embodiments, the center of the face can comprise the central one third of the length of the face extending from the heel end  16  to the toe end  18 , and/or can comprise the central one third of the height of the face extending from the top rail  18  to the sole  20 . 
     The lower portion of the front surface  351  near the bottom surface  354  of the insert  350  has a lower concentration of voids  360 . The lower portion of the insert  350  is positioned adjacent to a bottom portion of the face  322 , wherein the face  322  has minimal deflection. As such, the lower portion of the front surface  351  is able to damp vibrations caused by the impact, without inhibiting face  322  deflection or absorbing large amounts of energy. The result is a golf club head  300  comprising an insert  350 , wherein the insert  350  damps vibration to achieve desired impact acoustics, while not inhibiting face  322  deflection. Further, the insert  350  comprising a higher concentration of voids  360  near the top surface  353 , resulting in a majority of its mass distributed towards the bottom surfaces  354 . Therefore, the insert  350  can also be utilized as a swing weight aiding to move the club head  300  CG low and back. 
     Referring to  FIG. 12 , another embodiment of an insert  450  comprising voids  460  is displayed. The insert  450  is similar to inserts  150 ,  250 , and  350  and can comprise the same variations as described above, except the voids  460  extend from the heel end  456  to the toe end  455 . In the illustrated embodiment, the cross-sectional shape of the void  460  is hexagonal. In other embodiments, the cross-sectional shape can be circular, triangular, rectangular, or any other suitable shape. Further, the cross-sectional shape of the voids  460  can remain constant or can change across the length of the insert  450 . Further, the cross-sectional area of the voids  460  can increase, decrease or remain constant from the heel end  456  to the toe end  455 . As discussed above, the insert  450  can comprise a higher concentration of voids  460  near the top surface  453  than near the bottom surface  454 . The insert  450  can also vary according to any of the parameters described above with regards to inserts  50 ,  150 ,  250 ,  350 . 
     Referring to  FIG. 14 , insert  450  is shown in relation to a golf club head  400 . Golf club head  400  is similar to club head  10 ,  100 ,  200 , and  300 , except it comprises insert  450  having a plurality of voids  460  as the deflection feature. In the illustrated embodiment, the concentration of voids  460  can be greater near the front surface  451  than near the rear surface  452  of the insert  450 . Therefore, the spring constant or effective modulus can change across the depth (front surface  451  to rear surface  452 ) of the insert  450 . In these or other embodiments, during impact, the face  422  continues to deform or deflect until the spring constant of the insert  450  becomes too great. 
     Once the spring constant has reached a value wherein the force of impact can no longer compress the insert  450 , deformation of the face  422  ceases. The amount the insert  450  is able to deform directly correlates with the spring constant or effective modulus of the insert  450 . Therefore, altering the inserts  450  spring constant or effective modulus can alter the maximum face  422  deflection. As discussed above, the spring constant or effective modulus of the insert  450  can be altered by changing the material or geometry of the insert  450 . At the point of maximum deformation, the insert  450  can support the face plate  422  from further deformation or deflection to reduce the risk of reaching irreversible plastic deformation. The face  422  and insert  450  then rebound to their respective pre-impact positions, generating a desired spring-like effect, which can result in an increased golf ball speed and an increased golf ball travel distance. 
     II) Deflection Feature Comprising a Thinned Sole 
     As discussed above, the deflection feature of the golf club head  10  can further be a thin uniform sole. In some embodiments, the thinned uniform sole can be combined with one or more of the deflection features of the golf club head  10 ,  100 ,  200 ,  300 , and  400  discussed above.  FIG. 16  illustrates a golf club head  500  comprising a thin uniform sole  520 . The golf club head  500  is similar to the golf club heads  10 ,  100 ,  200 ,  300 ,  400 , except it comprises a thin uniform sole  520  as the deflection feature. The thin uniform sole  520  can extend from the face  522  to the rear end  524 . 
     The thin uniform sole  520  can provide multiple benefits. First, the thin uniform sole  520  can reduce stress on the face  522  caused during impact with the golf ball. Second, the thin uniform sole  520  can bend allowing the face  522  to experience greater deflection. Third, the thin uniform sole  520  removes weight from the sole area, allowing the weight to be redistributed in the rear end  524  of the golf club head  500 . At impact, the energy imparted to the face  522  by the golf ball can cause the thin uniform sole  520  to bend outward, which in turn increases the face  522  deflection. After bending, the thin uniform sole  520  rebounds back to its original position returning the majority of the energy from impact back to the golf ball. The result is a golf club head  500 , which imparts increased ball speeds and greater travel distances to the golf ball after impact. As a comparative, a club head without a thin uniform sole may have a sole thickness ranging from approximately 0.90 inches to approximately 1.5 inches. 
     In the illustrated embodiment, the thin uniform sole  520  comprises a sole thickness  521 , which remains constant from the face  522  to the rear end  524 . The shape of the sole  520  can follow the  3 -dimensional contour of the outer surface of the sole  520 . The uniform thin sole  520  also comprises a sole thickness  521 , which can be thinner than a conventional sole. For example, in some embodiments, the sole thickness  521  may range from approximately 0.15-0.85 inches. In other embodiments, the sole thickness  521  may be within the range of 0.15-0.35, 0.25-0.45, 0.35-0.55, 0.45-0.65, 0.55-0.75, or 0.65-0.85 inches. In other embodiments, the sole thickness may be approximately 0.15, 0.20, 0.25, 0.30, 0.35 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, or 0.85 inches. 
     Further, the thin uniform sole  520  can also be described as having a spring constant. Similar to inserts  50 ,  150 , 250 ,  350 ,  450 , the spring constant of the sole  520  can be calculated using Hookes law (defined above). To adjust the spring constant of the sole  520 , the material or sole thickness  521  can be adjusted. Having a thinner sole  520  results in a lower spring constant, which allows for greater bending of the sole  520  and thus, greater deflection in the face  522 , resulting in increased energy transfer back to a golf ball on impact due to a greater spring back force. In some embodiments, the sole  520  of the club head  500  can include a cascading region of thinning tiers, similar to the cascading sole described in U.S. patent application Ser. No. 14/920,480 entitled “Golf Club Heads with Energy Storage Characteristics.” 
     III) Deflection Feature Comprising a Cutout in Top Rail 
     As discussed above, the deflection feature of the golf club head  10  can be a cavity or undercut or cutout (hereafter cutout) in the top rail.  FIG. 17  illustrates the golf club head  700  comprising a cutout  770  in the top rail  718  adjacent to the rear surface of the face  722 . The golf club head  700  is similar to the golf club heads  10 ,  100 ,  200 ,  300 ,  400 , and  500 , except the golf club head  700  comprises a cutout  770  in the top rail  718  as the deflection feature. In some embodiments, the cutout  770  can be combined with one or more of the deflection features of the golf club head  10 ,  100 ,  200 ,  300 ,  400 , and  500  discussed above. 
     The cutout  770  can provide multiple benefits. First, the cutout  770  can increase face  722  deflection by lengthening the area across which the stress from impact is distributed. Second, the cutout  770  can increase flexibility in the top rail  718  of the golf club head  700 . Third, the cutout  770  can remove weight from the top rail  718 , allowing it to be redistributed in the lower rear end  724  of the golf club head  700 . 
     At impact, the energy imparted to the face  722  by the golf ball causes the face  722  to deflect. The cutout  770  can increase deflection in the face  722  by lowering the face  722  spring constant. Similar to inserts  50 ,  150 ,  25 ,  350 ,  450  or the uniform thin sole  520 , the spring constant of the face  722  can be calculated using Hookes law (defined above). The cutout  770  can adjust the spring constant of the face  722  by lengthening the area across which the stress from impact is spread. Having a longer area to absorb the stress, results in a lower spring constant. Having a face  722  with a lower spring constant creates a face  722  with greater deflection at the point of impact. 
     IV) Deflection Feature Comprising Optimized Face Materials 
     As discussed above, the deflection feature of the golf club head  10  can be a face comprising optimized materials. In some embodiments, the optimized material can be combined with one or more of the deflection features of the golf club head  10 ,  100 ,  200 ,  300 ,  400 ,  500 , and  700  discussed above. 
     The face  22  can be comprised solely of the optimized face material (not shown) or the face  22  can be comprised partially of the optimized face material and partially of a conventional face material. The optimized face material includes a strength-to-weight ratio or specific strength measured as the ratio of the yield strength to the density of the material. The optimized face material further includes a strength-to-modulus ratio or specific flexibility measured as the ratio of the yield strength to the elastic modulus of the material. 
     The optimized face material can have a specific strength greater than the specific strength of current known club head materials, while also having a reduced weight compared to a similar club head with known materials. Having an increased specific strength allows for a thinner face  22 , which can increase face  22  deflection. The reduced weight of the optimized face material can also allow the weight to be redistributed to the rear end  24  of the club head  10 . Further, the optimized face material can have a specific flexibility greater than the specific flexibility of current club head face materials. The face  22  having increased flexibility can reduce energy loss on impact with a golf ball, thereby increasing energy transfer to the ball resulting in increased ball speed and travel distance. 
     In some embodiments, the optimized face material can be a steel alloy having a specific strength of greater than or equal to 500,000 PSI/lb/in 3  (125 MPa/g/cm 3 ). For example, the specific strength of the steel alloy can be greater than or equal to 510,000 PSI/lb/in 3  (127 MPa/g/cm 3 ), greater than or equal to 520,000 PSI/lb/in 3  (130 MPa/g/cm 3 ), greater than or equal to 530,000 PSI/lb/in 3  (132 MPa/g/cm 3 ), greater than or equal to 540,000 PSI/lb/in 3  (135 MPa/g/cm 3 ), greater than or equal to 550,000 PSI/lb/in 3  (137 MPa/g/cm 3 ), greater than or equal to 560,000 PSI/lb/in 3  (139 MPa/g/cm 3 ), greater than or equal to 570,000 PSI/lb/in 3  (142 MPa/g/cm 3 ), greater than or equal to 580,000 PSI/lb/in 3  (144 MPa/g/cm 3 ), greater than or equal to 590,000 PSI/lb/in 3  (147 MPa/g/cm 3 ), greater than or equal to 600,000 PSI/lb/in 3  (149 MPa/g/cm 3 ), greater than or equal to 625,000 PSI/lb/in 3  (156 MPa/g/cm 3 ), greater than or equal to 675,000 PSI/lb/in 3  (168 MPa/g/cm 3 ), greater than or equal to 725,000 PSI/lb/in 3  (181 MPa/g/cm 3 ), greater than or equal to 775,000 PSI/lb/in 3  (193 MPa/g/cm 3 ), greater than or equal to 825,000 PSI/lb/in 3  (205 MPa/g/cm 3 ), greater than or equal to 875,000 PSI/lb/in 3  (218 MPa/g/cm 3 ), greater than or equal to 925,000 PSI/lb/in 3  (230 MPa/g/cm 3 ), or greater than or equal to 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ). 
     For further example, the specific strength of the steel alloy can be between 510,000 PSI/lb/in 3  (127 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 530,000 PSI/lb/in 3  (132 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 550,000 PSI/lb/in 3  (137 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 570,000 PSI/lb/in 3  (142 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 590,000 PSI/lb/in 3  (147 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 625,000 PSI/lb/in 3  (156 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 675,000 PSI/lb/in 3  (168 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 725,000 PSI/lb/in 3  (181 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), between 775,000 PSI/lb/in 3  (193 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ), or between 825,000 PSI/lb/in 3  (205 MPa/g/cm 3 ) and 975,000 PSI/lb/in 3  (243 MPa/g/cm 3 ). 
     Further, the specific flexibility of the steel alloy can be greater than or equal to 0.0060. For example, the specific flexibility of the steel alloy can be greater than or equal to 0.0062, greater than or equal to 0.0064, greater than or equal to 0.0066, greater than or equal to 0.0068, greater than or equal to 0.0070, greater than or equal to 0.0072, greater than or equal to 0.0076, greater than or equal to 0.0080, greater than or equal to 0.0084, greater than or equal to 0.0088, greater than or equal to 0.0092, greater than or equal to 0.0096, greater than or equal to 0.0100, greater than or equal to 0.0104, greater than or equal to 0.0108, greater than or equal to 0.0112, greater than or equal to 0.0116, greater than or equal to 0.0120, greater than or equal to 0.0125, greater than or equal to 0.0130, greater than or equal to 0.0135, or greater than or equal to 0.0140. 
     For further example, the specific flexibility of the steel alloy can be between 0.0060 and 0.0140, between 0.0062 and 0.0120, between 0.0064 and 0.0120, between 0.0066 and 0.0120, between 0.0068 and 0.0120, between 0.0070 and 0.0120, between 0.0080 and 0.0120, between 0.0088 and 0.0120, or between 0.0096 and 0.0120. 
     In some embodiments, the elongation of the steel alloy can be greater than 8%, greater than 9%, greater than 10° A, greater than 11%, greater than 12%, greater than 13%, greater than 14%, or greater than 15% to allow plastic deformation of the body to achieve bending for a desired loft and/or lie angle of the club head 10. 
     In embodiments, wherein the optimized face material is a steel alloy, the yield strength of the steel alloy can be greater than or equal to 170,000 PSI (1172 MPa), greater than or equal to 175,000 PSI (1207 MPa), greater than or equal to 180,000 PSI (1241 MPa), greater than or equal to 185,000 PSI (1276 MPa), greater than or equal to 190,000 PSI (1310 MPa), greater than or equal to 195,000 PSI (1344 MPa), greater than or equal to 200,000 PSI (1379 MPa), greater than or equal to 225,000 PSI (1551 MPa), or greater than or equal to 250,000 PSI (1724 MPa). Further, the yield strength of the steel alloy can be between 170,000 PSI (1172 MPa) and 250,000 PSI (1724 MPa), between 175,000 PSI (1207 MPa) and 250,000 PSI (1724 MPa), between 180,000 PSI (1241 MPa) and 250,000 PSI (1724 MPa), between 190,000 PSI (1310 MPa) and 250,000 PSI (1724 MPa), or between 200,000 PSI (1379 MPa) and 250,000 PSI (1724 MPa). 
     Further, the elastic modulus of the steel alloy can be less than or equal to 35,000,000 PSI (241,317 MPa), less than or equal to 32,500,000 PSI (224,080 MPa), less than or equal to 30,000,000 PSI (206,843 MPa), less than or equal to 28,000,000 PSI (193,053 MPa), less than or equal to 27,500,000 PSI (189,606 MPa), less than or equal to 27,000,000 PSI (186,159 MPa), less than or equal to 26,500,000 PSI (182,711 MPa), less than or equal to 26,000,000 PSI (179,264 MPa), less than or equal to 25,500,000 PSI (175,816 MPa), or less than or equal to 25,000,000 PSI (172,369 MPa). Further, the elastic modulus of the steel alloy can be between 25,000,000 PSI (172,369 MPa) and 35,000,000 PSI (241,317 MPa), between 25,000,000 PSI (172,369 MPa) and 30,000,000 PSI (206,843 MPa), or between 25,000,000 PSI (172,369 MPa) and 27,000,000 PSI (186,159 MPa). 
     Additionally, the density of the steel alloy can be less than or equal to 0.40 lb/in 3  (11.0 g/cm 3 ), less than or equal to 0.35 lb/in 3  (9.7g/cm 3 ), less than or equal to 0.30 lb/in 3  (8.3 g/cm 3 ), less than or equal to 0.29 lb/in 3  (8.0 g/cm 3 ), less than or equal to 0.28 lb/in 3  (7.8 g/cm 3 ), less than or equal to 0.27 lb/in 3  (7.5 g/cm 3 ), less than or equal to 0.26 lb/in 3  (7.2 g/cm 3 ), or less than or equal to 0.25 lb/in 3  (6.9 g/cm 3 ). Further, the density of the steel alloy can be between 0.25 lb/in 3  (6.9 g/cm 3 ) and 0.40 lb/in 3  (11.0 g/cm 3 ), between 0.25 lb/in 3  (6.9 g/cm 3 ) and 0.35 lb/in 3  (9.7g/cm 3 ), between 0.25 lb/in 3  (6.9 g/cm 3 ) and 0.30 lb/in 3  (8.3 g/cm 3 ), or between 0.25 lb/in 3  (6.9 g/cm 3 ) and 0.28 lb/in 3  (7.8 g/cm 3 ). 
     V) Deflection Feature Comprising Reinforcement Device 
       FIGS. 20-28  illustrate a golf club head  1000  having a deflection feature comprising a reinforcement device  1112 . The reinforcement device  1112  can be used to reinforce a thin face, thereby allowing increased face deflection and increased energy transfer to a golf ball (resulting in increased ball speed and travel distance). In some embodiments, the golf club head  1000  can further include one or more deflection feature of the golf club head  10 ,  100 ,  200 ,  300 ,  400 ,  500 , and  700  discussed above, including an insert, a thin uniform sole, or an optimized material and/or thin face. 
     Club head  1000  comprises an x-axis  1107 , a y-axis  1108 , and a z-axis  1109 . X-axis  1107 , y-axis  1108 , and z-axis  1109  provide a Cartesian reference frame for club head  1000 . Accordingly, x-axis  1107 , y-axis  1108 , and z-axis  1109  are perpendicular to each other. Further, x-axis  1107  extends through toe end  1104  and heel end  1106  and is equidistant between top end  1018  and bottom end  1020 ; y-axis  1108  extends through top end  1018  and bottom end  1020  and is equidistant between toe end  1104  and heel end  1106 ; and z-axis  1109  extends through front end  1203  ( FIG. 21 ) and rear end  1104  and is equidistant (i) between toe end  1104  and heel end  1106  and (ii) between top end  1018  and bottom end  1020 . In these or other embodiments, club head  1000  comprises a club head body  1012 . 
     Club head body  1012  can be solid, hollow, or partially hollow. When club head body  1012  is hollow and/or partially hollow, club head body  1012  can comprise a shell structure, and further, can be filled and/or partially filled with a filler material different from a material of shell structure. For example, the filler material can comprise a plastic foam. 
     Club head body  1012  comprises a face or face element  1022  and a reinforcement device  1112 . In many embodiments, club head body  1012  can comprise a perimeter wall element  1113 . 
     In many embodiments, face element  1022  comprises a face surface  1214  ( FIG. 21 ) and a rear surface  1115 . Meanwhile, face surface  1214  ( FIG. 21 ) comprises a face center  1216  ( FIG. 21 ) and a face perimeter  1217  ( FIG. 21 ), and rear surface  1115  comprises a rear center  1118  and a rear perimeter  1119 . Face surface  1214  ( FIG. 21 ) can refer to a striking face or a striking plate of club head  1000 , and can be configured to impact a ball (not shown), such as, for example, a golf ball. 
     In these or other embodiments, face surface  1214  ( FIG. 21 ) can be located at front end  1203  ( FIG. 21 ), and rear surface  1115  can be located at rear end  1104 . Further, rear surface  1115  can be approximately opposite to face surface  1214  ( FIG. 21 ); rear center  1118  can be approximately opposite face center  1216  ( FIG. 21 ); and rear perimeter  1119  can be approximately opposite face perimeter  1217  ( FIG. 21 ). Generally, in many examples, face center  1216  ( FIG. 21 ) can refer to a geometric center of face surface  1214  ( FIG. 21 ). Accordingly, in these or other examples, face center  1216  ( FIG. 21 ) can refer to a location at face surface  1214  ( FIG. 21 ) that is approximately equidistant between toe end  1014  and heel end  1016  and further that is approximately equidistant between top end or top rail  1018  and bottom end or sole  1020 . In various examples, the face center can refer to the face center as defined at  United States Golf Association: Procedure for Measuring the Flexibility of a Golf Clubhead , USGA-TPX 3004, Revision 1.0.0, p. 6, May 1, 2008 (retrieved May 12, 2014 from http://www.usga.org/equipment/testing/protocols/Test-Protocols-For-Equipment), which is incorporated herein by reference. Likewise, in some examples, rear center  1118  can refer to a geometric center of rear surface  1115 . 
     By reference, x-axis  1107  and y-axis  1108  can extend approximately parallel to face surface  1214  ( FIG. 20 ), and z-axis  1109  can extend approximately perpendicular to face surface  1214  ( FIG. 20 ). Meanwhile, each of x-axis  1107 , y-axis  1108 , and z-axis  1109  can intersect rear center  1118  such that rear center  1118  comprises the origin of the Cartesian reference frame provided by x-axis  1107 , y-axis  1108 , and z-axis  1109 . 
     In various embodiments, grooves  1026  ( FIG. 21 ) can comprise one or more grooves, respectively, and can extend between toe end  1014  and heel end  1016 . In these or other embodiments, grooves  1026  ( FIG. 21 ) can be approximately parallel to x-axis  1107 . 
     In many embodiments, reinforcement device  1112  comprises one or more reinforcement elements  1120  (e.g., reinforcement element  1121 ). Reinforcement device  1112  and/or reinforcement element(s)  1120  are located at rear surface  1115  and extend out from rear surface  1115  toward rear end  1024  and away from the face or front end  1022  ( FIG. 20 ). In many embodiments, each reinforcement element of reinforcement element(s)  1120  comprises an outer perimeter surface and a geometric center. In these or other embodiments, the geometric center(s) of one or more of reinforcement element(s)  1120  (e.g., reinforcement element  1121 ) can be located approximately at z-axis  1109 . For example, reinforcement element  1121  can comprise outer perimeter surface  1126  and geometric center  1130 . As discussed above, golf club heads  10 ,  100 ,  200 ,  300 ,  400 ,  500 , and  700  can comprise the reinforcement device  1112  as described below. 
     Reinforcement device  1112  and reinforcement element(s)  1120  are configured to reinforce face element  1022  while still permitting face element  1022  to bend, such as, for example, when face surface  1214  ( FIG. 21 ) impacts a ball (e.g., a golf ball). As a result, face element  1022  can be thinned to permit mass from face element  1022  to be redistributed to other parts of club head  1000  and to make face element  1022  more flexible without buckling and failing under the resulting bending. Advantageously, because face element  1022  can be thinner when implemented with reinforcement device  1112  and reinforcement element(s)  1120  than when implemented without reinforcement device  1112  and reinforcement element(s)  1120 , the center of gravity, the moment of inertia, and the coefficient of restitution of club head  1000  can also be altered to improve the performance characteristics of club head  1000 . For example, implementing reinforcement device  1112  and reinforcement element(s)  1120  can increase a flight distance of a golf ball hit with face surface  1214  ( FIG. 21 ) by increasing a launch angle of the golf ball (e.g., by approximately 1-3 tenths of a degree), increase the ball speed of the golf ball (e.g., by approximately 0.1 miles per hour (mph) (0.161 kilometers per hour (kph) to approximately 3.0 mph (4.83 kph)), and/or decreasing a spin of the golf ball (e.g., by approximately 1-500 rotations per minute). In these examples, reinforcement device  1112  and reinforcement element(s)  1120  can have the effect of countering some of the gearing on the golf ball provided by face surface  1214  ( FIG. 21 ). 
     Testing of golf clubs comprising an embodiment of golf club head  1000  was performed. Overall, when compared to an iron golf club with a standard reinforced strikeface and custom tuning port, the testing showed more forgiveness, as indicated by higher moments of inertia around the x-axis and/or the y-axis and a tighter statistical area of the impact of the golf ball on the face of the golf club head. In some testing, the moment of inertia about the x-axis increased by approximately 2%, the moment of inertia about the y-axis increased by approximately 4%, and/or the statistical area of the impact of the golf ball on the face of the golf club head was reduced by approximately 15-50 percent. Additionally, when compared to an iron golf club with a standard reinforced strikeface and custom tuning port, the testing showed increased ball speed of the golf ball, higher launch angle of the golf ball, and/or decreased spin of the golf ball were found. As an example, in testing an embodiment of golf club  1000  on a 5 iron golf club, it was found that the ball speed of the golf ball increased by approximately 1.5 mph (2.41 kph), the golf ball had an approximately 0.3 degree higher launch angle, and the spin of the golf ball decreased by approximately 250 revolutions per minute (rpm). In another example, in testing an embodiment of golf club  10  on a 7 iron golf club, it was found that the ball speed of the golf ball increased by approximately 2.0 mph (3.22 kph), the golf ball had approximately no launch angle degree change, and the spin of the golf ball decreased by approximately 450 rpm. As an additional example, in testing an embodiment of golf club  1000  on a wedge iron golf club, it was found that the ball speed of the golf ball had approximately no change in speed, the golf ball had an approximately 0.1 degree higher launch angle, and the spin of the golf ball decreased by approximately 200 rpm. 
     Notably, in many examples, when face element  1022  comprises grooves  1026  ( FIG. 21 ) and face element  1022  is thinned without implementing reinforcement device  1112  and reinforcement element(s)  1120 , buckling and failure of face element  1111  can occur at the bottom of grooves  1026 , particularly at grooves  1022  ( FIG. 21 ) proximal to face center  1216  ( FIG. 21 ), as illustrated at  FIGS. 22 &amp; 23  and described as follows with respect to  FIGS. 22 &amp; 23 . 
     Club head  1000  having reinforcement device  1112  may also have a uniform transition thickness  1550  ( FIG. 24 ), similar to the thin sole described above. The uniform transition thickness extends from front end  1203  to sole  1020 . Uniform transition thickness  1550  absorbs stress directed to the region of club head  1000  having reinforcement device  1112  between front end  1203  and sole  1020 . Uniform transition thickness  1550  may range from approximately 0.20-0.80 inches. For example, uniform transition thickness  1550  may be approximately 0.20, 0.25, 0.30, 0.35 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, or 0.80 inches. 
     Specifically, turning ahead in the drawings,  FIG. 22  illustrates conventional club head  3000 , according to an embodiment. Club head  3000  can be similar to club head  1000  ( FIGS. 20 &amp; 21 ), but unlike club head  1000 , is devoid of a reinforcement device and reinforcement elements at rear surface  1315  of face element  1022  of club head  3000 . Club head  3000  comprises one or more grooves  3026  at face surface  1314  of club head  3000 . Rear surface  1315  can be similar to rear surface  1115  ( FIG. 21 ); face element of club head  3000  can be similar or identical to face element  1022  ( FIG. 21 ); face surface  1314  can be similar or identical to face surface  1214  ( FIG. 21 ); and/or grooves  3026  of club head  3000  can be similar or identical to grooves  1026  of club head  1000  ( FIG. 21 ). Meanwhile,  FIG. 23  illustrates a stress-strain analysis of a partial cross-sectional view of club head  3000  taken along section line  4 - 4  of  FIG. 22  simulating face surface  1314  of club head  3000  impacting a golf ball (not shown) where the resulting bending is multiplied three-fold, according to the embodiment of  FIG. 22 . 
     As demonstrated at  FIG. 23 , face element  1022  behaves similarly to a simply supported beam and thus comprises neutral axis  1436 . The portion of face element  1022  between face surface  1314  and neutral axis  1436  is in compression, and the portion of face element  1022  between neutral axis  1436  and rear surface  1315  is in tension. Stress builds first at face surface  1314  and rear surface  1315  and moves inward toward neutral axis  1436 . However, unlike a simply supported beam, face element  1311  also comprises grooves  1026  at the portion of face element  1022  that is in compression. When face element  1022  bends too much, the mechanical yield of face element  1022  in the bottom of grooves  1026  can be reached. If not for grooves  1026 , face element  1022  would ordinarily be expected to fail first in the portion of face element  1022  that is under tension, but grooves  1026  cause failure to occur first at the portion of face element  1022  that is in compression. Namely, face element  1022  fails at grooves  1026  before the remainder of face element  1022  has a chance to reach high enough stress levels to result in failure. Iron-type club heads can be more susceptible to failure at grooves because iron-type club heads tend to be flat at face surface  1314 , unlike wood-type golf club head which tend to be convex at face surface  1314 . As a result, when wood-type golf club heads bend at face surface  1314 , face surface  1314  can still be bowed somewhat outward. On the other hand, when iron-type golf club heads bend at face surface  1314 , face surface  1314  can bend to a concave shape that increases the extent of the compression at the portion of face element  22  that is under compression. 
     Turning now back to  FIGS. 20 and 21 , implementing reinforcement device  1112  and reinforcement element(s)  1120  can reinforce a localized bending in grooves  1026  ( FIG. 21 ), particularly in those grooves  1026  that are proximal to face center  1216  ( FIG. 21 ), while permitting increased overall bending in face element  1111 . Reinforcement device  1112  and reinforcement element(s)  1120  are able to provide these benefits by increasing the localized thickness of face element  1022 , making face element  1022  stiffer and harder in those locations. In effect, reinforcement device  1112  and reinforcement element(s)  1120  are operable to pull a neutral axis of face element  1022  away from face surface  1214  ( FIG. 21 ) and closer to rear surface  1115 . 
     Meanwhile, reinforcement device  1112  and reinforcement element(s)  1120  are further able to provide these benefits when implemented as a closed structure (e.g., one or more looped ribs) because such closed structures are able to resist deformation as a result of circumferential (i.e., hoop) stresses acting on reinforcement device  1112  and reinforcement element(s)  1120 . For example, circumferential (i.e., hoop) stresses acting on reinforcement device  1112  and reinforcement element(s)  1120  can prevent opposing sides of reinforcement device  1112  and reinforcement element(s)  1120  from rotating away from each other, thereby reducing bending. 
     In implementation, reinforcement element(s)  1120  (e.g., reinforcement element  1121 ) can be implemented in any suitable shape(s) (e.g., polygonal, elliptical, circular, etc.) and/or in any suitable arrangement(s) configured to perform the intended functionality of reinforcement device  1112  and/or reinforcement element(s)  1120  as described above. Further, when reinforcement element(s)  1120  comprise multiple reinforcement elements, two or more reinforcement elements of reinforcement element(s)  1120  can be similar to another, and/or two or more reinforcement elements of reinforcement element(s)  1120  can be different from another. 
     In some embodiments, reinforcement element(s)  1120  (e.g., reinforcement element  1121 ) can be symmetric about x-axis  1107  and/or y-axis  1108 . When reinforcement element(s)  1120  (e.g., reinforcement element  1121 ) are implemented with an oblong shape, in many embodiments, a largest dimension (e.g., major axis) of the reinforcement element(s) can be parallel and/or co-linear with one of x-axis  1107  or y-axis  1108 . However, in other embodiments, the largest dimension (e.g., major axis) can be angled with respect to x-axis  1107  and/or y-axis  1108 , as desired. Further, in many embodiments, reinforcement element(s)  1120  (e.g., reinforcement element  1121 ) can be centered at z-axis  1109 , but in some embodiments, one or more of reinforcement element(s)  1120  (e.g., reinforcement element  1121 ) can be biased off-center of z-axis  1109 , such as, for example, biased toward one or two of top end  1018 , bottom end  1020 , toe end  1014 , and heel end  1016 . 
     In many embodiments, each reinforcement element of reinforcement element(s)  1120  (e.g., reinforcement element  1121 ) can comprise one or more looped ribs  1127  (e.g., looped rib  1122 ). Specifically, reinforcement element  1121  can comprise looped rib  1122 . In these or other embodiments, when looped rib(s)  1127  comprise multiple looped ribs, looped rib(s)  1127  can be concentric with each other about a point and/or axis (e.g., z-axis  1109 ). In other embodiments, when looped rib(s)  1127  comprise multiple looped ribs, looped rib(s)  1127  can be concentric with each other about a point and/or axis. In other embodiments, when looped rib(s)  1127  comprise multiple looped ribs, two or more of looped rib(s)  1127  can be nonconcentric. Further, in these or other embodiments, two or more of looped rib(s)  1127  can overlap. Meanwhile, in these embodiments, looped rib  1122  can comprise an elliptical looped rib, and in some of these embodiments, looped rib  1122  can comprise a circular looped rib. As noted above, implementing reinforcement element(s)  120  as looped rib(s)  1127  can be advantageous because of the circumferential (e.g., hoop) stress provided by the closed structure of looped rib(s)  1127 . In many embodiments, one or more of (or each of) looped rib(s)  1127  is a continuous closed loop. 
     In these or other embodiments, each looped rib of looped rib(s)  1127  comprises an outer perimeter surface and an inner perimeter surface. Meanwhile, in these embodiments, the outer perimeter surface of each reinforcement element (e.g., reinforcement element  121 ) comprises the outer perimeter surface of the looped rib corresponding to that reinforcement element (e.g., looped rib  1122 ). For example, looped rib  1122  can comprise outer perimeter surface  1128  and inner perimeter surface  1129 . Further, inner perimeter surface  1129  can be steep and substantially orthogonal at rib height  1540  ( FIG. 28 ) relative to the rear surface. 
     In some embodiments, one or more outer perimeter surface(s) of reinforcement element(s)  1120  (e.g., outer perimeter surface  1126  of reinforcement element  1121 ) can be filleted with rear surface  1115 . In these or other embodiments, one or more inner perimeter surface(s) of looped rib(s)  1127  (e.g., inner perimeter surface  1129  of looped rib  1122 ) can be filleted with rear surface  1115 . Filleting the outer perimeter surface(s) of reinforcement element(s)  1120  (e.g., outer perimeter surface  1126  of reinforcement element  1121 ) with rear surface  1115  can permit a smooth transition of reinforcement element(s)  1120  (e.g., outer perimeter surface  1126  of reinforcement element  1121 ) into rear surface  1115 . Meanwhile, inner perimeter surface(s) of looped rib(s)  1127  (e.g., inner perimeter surface  1129  of looped rib  1122 ) can be filleted with rear surface  1115  with a fillet having a radius of greater than or equal to approximately 0.012 centimeters. 
     The reinforcement element on the rear surface of the face element comprising a fillet between the outer perimeter of the reinforcement element and the rear surface of the face element, beneficially allows impact stresses to be transferred from the face element into the reinforcement element. 
     The transfer of impact stress away from the face element and into the reinforcement element allows the center of the face element to be thinned to increase face deflection and ball speed on impact with a golf ball. Accordingly, the face element can be thinner within the inner perimeter surface than without or outside the outer perimeter surface of the reinforcement element. 
     In some embodiments, when reinforcement element  1121  comprises looped rib  1122 , looped rib  1122  can comprise cavity  1131 . In other embodiments, when reinforcement element  1121  comprises looped rib  1122 , looped rib  1122  does not comprise cavity  1131 . In embodiments without cavity  1131 , the center thickness  1537  ( FIGS. 24 and 13 ) can be greater than in embodiments with cavity  1131  and can be less than or equal to the face thickness at rib height  1542  ( FIGS. 24 and 28 ), which can be measured from face surface  1214  ( FIG. 21 ) to the distal end of looped rib  1122  (e.g., the combined distance of center thickness  1537  ( FIG. 24 ) and rib height  1542  ( FIG. 24 )). Cavity  1131  is defined by inner perimeter surface  1129  and rear surface  1115 . In some embodiments, cavity  1131  can be a central cavity. In many embodiments, cavity  1131  can be devoid of any contents, such as, for example, a weighted insert. In other embodiments, cavity  1131  can contain an insert  1805  as shown in  FIGS. 26 and 27 . These inserts can be similar to insert  50 ,  150 ,  250 ,  350 , and  450 . 
     As discussed in some detail above, by implementing reinforcement device  1112  and reinforcement element(s)  1120 , face surface  1214  ( FIG. 21 ) can be nearer to rear surface  1115  (i.e., thinner) proximal to (e.g., at) face center  1216  ( FIG. 21 ) than proximal to (e.g., at) face perimeter  1217  ( FIG. 21 ). In some embodiments, a portion of face surface  1214  ( FIG. 21 ) that is proximal to face center  1216  ( FIG. 21 ) can refer to a portion of the surface area of face surface  1214  bounding face center  1216  ( FIG. 21 ) and representing approximately one percent, two percent, three percent, five percent, ten percent, or twenty percent of a total surface area of face surface  1214 . In these or other embodiments, the portion of the surface area of face surface  1214  ( FIG. 21 ) can correspond to a portion of the surface area of rear face  1115  covered by reinforcement element  1121 . Meanwhile, in some embodiments, a portion of face surface  1214  ( FIG. 21 ) that is proximal to face perimeter  1217  ( FIG. 21 ) can refer to a region of face surface  1214  bounded by face perimeter  1217  and an inset boundary located approximately 0.10 centimeters, 0.20 centimeters, 0.25 centimeters, 0.50 centimeters, 1.00 centimeters, or 2.00 centimeters from face perimeter  1217  ( FIG. 21 ). 
     Turning ahead briefly in the drawings,  FIGS. 24 and 28  illustrate a cross-sectional view of club head  1000  taken along section line  5 - 5  of  FIG. 21 , according to the embodiment of  FIG. 20 . Club head  1000  can comprise center thickness  1537 . Center face thickness  1537  can refer to a distance from face center  1216  ( FIG. 21 ) to rear center  1118  ( FIG. 20 ). In many embodiments, center thickness  1537  can be approximately 0.150 cm to approximately 0.300 cm. In some embodiments, center thickness  1537  can be less than 0.300 cm, less than 0.255 cm, less than 0.250 cm, less than 0.205 cm, less than 0.200 cm, or less than 0.155 cm. In some embodiments, the center of reinforcement element  1120  can be at least partially filled in. For example, the center of reinforcement element  1120  can be filled in with a damping material or a vibration attenuating feature (e.g., insert  1805  ( FIG. 27 )) or other material. In many embodiments, center thickness  1537  can be thinner than a face thickness at rib height  1540 . In other embodiments, center thickness  1537  can be approximately equal to the face thickness at rib height  1540 . The face thickness at rib height  1540  can be rib height  1540  added to center thickness  1537 . In many embodiments, face thickness  1542  outside of reinforcement element  1120  can be thicker than center thickness  1537 , but thinner than the face thickness at rib height  1540 . In other embodiments, face thickness  1542  can be the same as center thickness  1537 . In many embodiments, a center thickness from the face center  1216  to the rear center  1118  is less than or equal to approximately 0.203 centimeters. 
     In some embodiments, a width of the rib can change throughout looped rib  1122  ( FIG. 20 ), In some embodiments, looped rib  1122  ( FIG. 20 ) and/or inner perimeter surface  1129  ( FIG. 20 ) can comprise largest rib span  1538 . Largest rib span  1538  can refer to the largest distance from one side of inner perimeter surface  1129  ( FIG. 20 ) across to an opposing side of inner perimeter surface  1129  ( FIG. 20 ) measured parallel to rear surface  1115  ( FIG. 20 ). Accordingly, when looped rib  1122  ( FIG. 20 ) comprises an elliptical looped rib, largest rib span  1538  can refer to a major axis of inner perimeter surface  1129  ( FIG. 20 ). Further, when looped rib  1122  ( FIG. 20 ) comprises a circular looped rib, largest rib span  1538  can refer to a diameter of inner perimeter surface  1129  ( FIG. 20 ). Notably, in many embodiments, largest rib span  1538  can be measured at a midpoint of inner perimeter surface  1129  ( FIG. 20 ). 
     In some embodiments, largest rib span  1538  can be approximately 0.609 cm to approximately 1.88 cm. In some embodiments, largest rib span  1538  can be approximately 1.0 cm. In some embodiments, when largest span  1538  is too large (e.g., greater than approximately 1.88 centimeters), looped rib  1122  ( FIG. 20 ) can be insufficient to reinforce grooves  1028  ( FIG. 21 ) nearest to face center  1216  ( FIG. 21 ). Meanwhile, in these or other embodiments, when largest span  1538  is too small (e.g., less than approximately 0.609 centimeters), looped rib  1122  can be insufficient to reinforce grooves  1028  ( FIG. 21 ) nearest to face perimeter  1217  ( FIG. 21 ). Generally, these upper and lower limits on largest rib span  1538  can be a function of a size of face element  1111  ( FIG. 20 ). 
     The rib span plays an important role in the amount of stress that is transferred from the face element into the end portion or rear end of the reinforcement device due to the fillet. Specifically, the rib span transfers the stress of impact generated at the face into a hoop stress within the reinforcement device. A rib span smaller than the described rib span can result in a large portion of the impact stress concentrating on the front and rear of the face element around the perimeter of the reinforcement element, creating a stress rise on the face element. A rib span larger than the described rib span can result in a large portion of the impact stress concentrating centrally on the front and rear of the face element, creating a stress riser on the face element. The described rib span corresponding to the impact area of a golf ball, in combination with the fillet, results in the significant stresses being transferred away from the face element and into the reinforcement device, thereby reducing the stress on the face element. 
     In some embodiments, two or more ribs  1621  and  1641  can be present, for example as shown in  FIG. 25 . In this case, the larger rib span or inner or outer diameter of rib  1641  ( FIG. 25 ) can be greater than 1.88 centimeters, and the smaller rib span or inner or outer diameter of rib  1621  ( FIG. 25 ) can be less than 0.609 centimeters. 
     Further, looped rib  1122  ( FIG. 20 ) can comprise a rib thickness  1539 . Rib thickness  1539  can refer to a distance between inner perimeter surface  1129  ( FIG. 20 ) of looped rib  1122  ( FIG. 20 ) and outer perimeter surface  1128  ( FIG. 20 ) of looped rib  1122  ( FIG. 20 ) measured parallel to rear surface  1115  ( FIG. 20 ). In some embodiments, the thickness of looped rib  1122  ( FIG. 20 ) can vary throughout looped rib  1122  ( FIG. 20 ), and rib thickness  1539  can be a maximum rib thickness of looped rib  1122  ( FIG. 20 ). In many embodiments, rib thickness  1539  can be approximately 0.050 cm to approximately 1.50 cm. In some embodiments, rib thickness  1539  can be approximately 0.05 cm. In some embodiments, rib thickness  1539  can be greater than or equal to approximately 0.25 centimeters. In some embodiments, rib thickness  539  can be approximately 0.50 centimeters. In some embodiments, rib thickness  539  can be approximately 0.75 centimeters. In some embodiments, rib thickness  539  can be approximately 1.00 centimeters. In some embodiments, rib thickness  539  can be approximately 1.25 centimeters. In some embodiments, rib thickness  539  can be approximately 1.50 centimeters. In various embodiments, when looped rib(s)  1127  ( FIG. 20 ) comprises multiple looped ribs, two or more looped ribs of looped rib(s)  1127  ( FIG. 20 ) can comprise the same rib thicknesses, and/or two or more looped ribs of looped rib(s)  1127  ( FIG. 20 ) can comprise different rib thicknesses. Notably, in many embodiments, rib span  1539  can be measured at a midpoint of inner perimeter surface  1129  ( FIG. 20 ) and/or outer perimeter surface  1128  ( FIG. 20 ). 
     Further still, looped rib  1122  ( FIG. 20 ) can comprise rib height  1540 . Rib height  1540  can refer to a distance perpendicular from rear surface  1115  ( FIG. 20 ) to a center location of looped rib  1122  ( FIG. 20 ) farthest from rear surface  1115  (i.e., where outer perimeter surface  1128  ( FIG. 20 ) interfaces with inner perimeter surface  1129  ( FIG. 20 ). In these or other embodiments, rib height  1540  can be greater than or equal to approximately 0.3048 centimeters. In some embodiments, rib height  1540  can be approximately 0.1778 cm to approximately 0.3048 cm. In some embodiments, rib height  1540  can be approximately 0.17 cm, 0.20 cm, 0.23 cm, 0.26 cm, 0.29 cm, or 0.30 cm. In many embodiments, rib height  1540  can be less than or equal to approximately 0.512 cm. In some embodiments, the height of looped rib  1122  ( FIG. 20 ) can vary throughout looped rib  1122 , and rib height  1540  can be a maximum rib height of looped rib  1122  ( FIG. 20 ). In various embodiments, when looped rib(s)  1127  ( FIG. 20 ) comprises multiple looped ribs, two or more looped ribs of looped rib(s)  1127  ( FIG. 20 ) can comprise the same rib heights, and/or two or more looped ribs of looped rib(s)  1127  ( FIG. 20 ) can comprise different rib heights. 
     In many embodiments, center thickness  1537 , largest rib span  1538 , rib thickness  1539 , and/or rib height  1540  can depend on one or more of each other. For example, center thickness  1537  can be a function of rib thickness  1539  and rib height  1540 . That is, for an increase in rib thickness  1539  and/or rib height  1540 , center thickness  1537  can be decreased, and vice versa. Meanwhile, rib thickness  1539  and rib height  1540  can be dependent on each other. For example, increasing rib thickness  1539  can permit rib height  1540  to be decreased, and vice versa. 
     Returning now to  FIGS. 20 &amp; 21 , in many embodiments, perimeter wall element  1113  can comprise a first perimeter wall portion  1124  and a second perimeter wall portion  1125 . Perimeter wall element  1113  extends (i) at least partially (e.g., entirely) around rear perimeter  1119  of rear surface  1115 , (ii) out from rear surface  1115  toward rear end  1104  and (iii) away from front end  1203  ( FIG. 21 ). Meanwhile, first perimeter wall portion  1124  can extend along rear perimeter  1119  of rear surface  1115  at top end  1101 , and second perimeter wall portion  1125  can extend along rear perimeter  1119  of rear surface  1115  at bottom end  1102 . In many embodiments, reinforcement device  1112  and reinforcement element(s)  1120  are separate and/or located away from perimeter wall element  1113  at rear surface  1115  so that reinforcement device  1112  and reinforcement element(s)  1120  float at rear surface  1115 . By floating reinforcement device  1112  and reinforcement element(s)  1120 , face element  1111  can be permitted to bend approximately symmetrically about face center  1216  ( FIG. 21 ). 
     In many embodiments, club head body  1012  can comprise (i) a top surface  1132  at least partially at first perimeter wall portion  1124  and/or top end  1101 , and/or (ii) a sole surface  1133  at least partially at second perimeter wall portion  1125  and/or bottom end  1102 . Accordingly, in some embodiments, first perimeter wall portion  1124  can comprise at least part of top surface  1132 ; and/or second perimeter wall portion  1125  can comprise at least part of sole surface  1133 . Further, top surface  1132  can interface with face surface  1214  ( FIG. 21 ) at top end  1101 ; and/or sole surface  1133  can interface with face surface  1214  ( FIG. 21 ) at bottom end  1102 . 
     In some embodiments, at least part of second perimeter wall portion  1125  can be approximately equal thickness with or thinner than face element  1111  at face perimeter  1217  ( FIG. 21 ) and/or proximal to face perimeter  1217 . For example, second perimeter wall portion  1125  can be equal thickness with or thinner than face element  1111  at face perimeter  1217  ( FIG. 21 ) and/or proximal to face perimeter  1217  at a portion of second perimeter wall portion  1125  that is proximal to face perimeter  1217  (i.e., where second perimeter wall portion  1125  interfaces with face element  1111 ). Implementing this portion of second perimeter wall portion  1125  to be equal thickness with or thinner than face element  1111  at face perimeter  1217  ( FIG. 21 ) and/or proximal to face perimeter  1217  can prevent stress risers from forming at second perimeter wall portion  1125  when face surface  1214  ( FIG. 21 ) impacts a golf ball. 
     Rear surface  1115  comprises a first rear surface portion and a second rear surface portion. The first rear surface portion can refer to the part of rear surface  1115  covered by perimeter wall element  1113 , and the second rear surface portion can refer to the remaining part of rear surface  1115 . In many embodiments, reinforcement element  1121  (e.g., looped rib  1122 ) can cover greater than or equal to approximately  25  percent of a surface area of the second rear surface portion of rear surface  1115  and/or less than or equal to approximately 40 percent of a surface area of the second rear surface portion of rear surface  1115 . In other embodiments, reinforcement element  1121  (e.g., looped rib  1122 ) can cover greater than or equal to approximately 30 percent of a surface area of the second rear surface portion of rear surface  1115 . In some embodiments, reinforcement element  1121  (e.g., looped rib  1122 ) can cover approximately 25 percent, 28 percent, 31 percent, 34 percent, 37 percent or 40 percent of a surface area of the second rear surface portion of rear surface  1115 . 
     Referring to  FIGS. 26 and 27 , in some embodiments, insert  1805  can be a vibration attenuating feature. Insert  1805  can be a non-metallic material, an elastomeric material such as polyurethane, or another material such as foam. Insert  1805  can be used to adjust the sound and feel of club head  1000 . By absorbing or damping vibration, insert  1805  improves the feel of club head  1000 . In addition, insert  1805  absorbs the sound of a golf ball striking the face, making golf club  1000  head feel less hollow and more solid. In further embodiments, a badge (not shown) can at least partially cover cavity  1131 . The badge can be separate from insert  1805  or can be integral with insert  1805 . In other embodiments, the badge can be integral with the reinforcement element, such as reinforcement element  1120  ( FIG. 20 ). 
     In some cases, the weight of insert  1805  can be less than about 3 g so as to not significantly affect the swing weight or the center of gravity of club head  1000 . In other embodiments, insert  1805  weight can be more than about 3 g, such as about 5 g to about 10 g, and can contribute substantially to the swing weight and/or the center of gravity of club head  800 . In some embodiments, insert  1805  can be adhered to cavity  1131  using an epoxy adhesive, a viscoelastic foam tape, the vibration attenuating feature, or a high strength tape such as 3M™ VHB™ tape. In other embodiments, insert  1805  can be poured and bonded directly into cavity  1131 . The badge can be bonded with similar adhesives. In some embodiments, insert  1805  or the badge can be flush with looped rib  1122  ( FIG. 1 ) at the top of rib height  1540 , or they can be below rib height  1540  when fully assembled. 
     In some embodiments, at least one vibration attenuating feature (e.g., insert  1805  ( FIG. 28 ) can be disposed on rear surface  1115  ( FIG. 20 ) of the golf club head, such as golf club head  1000 . The vibration attenuating feature can produce a more desirable sound from the golf club head  1000  upon impact. The thin face element  1111  ( FIG. 20 ) of golf club head  1000  can cause undesirable sounds when striking a golf ball. The vibration attenuating feature can reduce the vibrations leading to a more desirable sound on impact by thin face element  1111  ( FIG. 20 ). By providing a more desirable noise, the vibration attenuating component can increase a user&#39;s confidence during use. The vibration attenuating feature can also reduce the vibrational shock felt by the user of the golf club upon striking the golf ball. Furthermore, the vibration attenuating feature may reduce vibrational fatigue to decrease wear on golf club  1000  and various features such as, but not limited to, cavity  1131  or weight cavity  1135  ( FIG. 20 ). The reduced vibrational fatigue can further lower the risk of loosening or displacement of parts such as, but not limited to, insert  1805  of cavity  1131  or an insert in weight cavity  1135  ( FIG. 20 ). The reduced vibrational fatigue may extend the performance life of golf club head  1000 . 
     In further embodiments, the vibration attenuating feature may comprise at least one layer of a viscoelastic damping material. The damping material may comprise a pressure sensitive viscoelastic acrylic polymer and aluminum foil forming a damping foil such as 3M™ Damping Foil Tape. The damping foil may comprise an adhesive layer. In one embodiment the vibration attenuating feature may comprise at least one viscoelastic adhesive layer which may comprise a composition of varying layers of at least one layer of epoxy adhesive, a viscoelastic foam tape, and/or a high strength tape such as 3M™ VHB™ tape. In some embodiments, the vibration attenuating feature may comprise various layer combinations of at least one of viscoelastic adhesive, damping foil, and/or a badge. 
     Returning to  FIG. 26 , in some embodiments, the vibration attenuating feature can be disposed on the rear surface  1115  ( FIG. 20 ) of the golf club head, such as golf club head  1000 , which comprises a rear surface material such as iron steel. In another embodiment, the vibration attenuating feature can be disposed in cavity  1131 , or on or under insert  1805  of the golf club head  1000 . The vibration attenuating feature can be located in various locations of the rear surface  1115  ( FIG. 20 ) of the golf club head  1000 . Generally, the vibration attenuating feature is at least partially located under the profile of the badge on the rear surface  1115  ( FIG. 20 ). In some embodiments, the vibration attenuating feature is disposed under the entirety of the badge profile. In other embodiments, the vibration attenuating feature is at least partially disposed under only particular regions of the badge profile such as the aluminum or elastomer regions. The vibration attenuating feature can be disposed under only at least part of the perimeter region of the badge profile. In some embodiments the vibration attenuating feature can be disposed at least partially in cavity  1131  of the golf club head  1000 . The vibration attenuating feature may be disposed at least partially on or under insert  1805  within cavity  1131 . In many embodiments the disposition of the vibration attenuating feature on golf club head  1000  will comprise varying combinations the foil being disposed at least partially under the badge, at least partially over insert  1805 , at least partially in weight cavity  1135  ( FIG. 1 ), and/or at least partially in cavity  1131 . In some embodiments, the vibration attenuating feature will be disposed such that it covers at least 10 percent of the surface area of rear surface  1115  ( FIG. 20 ). In other embodiments, the vibration attenuating feature may cover at least 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 percent of the surface area of rear surface  1115 . 
     VI) Golf Club Head Comprising a Dual Density Weight 
     Instead of, or in addition to each of the aforementioned deflection features, the golf club head  10  can comprise a dual density weight.  FIG. 18  illustrates the golf club head  800  comprising a dual density weight  880  positioned in the rear end  824  of the golf club head  800 . The golf club head  800  is similar to golf club heads  10 ,  100 ,  200 ,  300 ,  400 ,  500 , and  700 , except golf club head  800  comprises a dual density weight  880 . In some embodiments, the golf club head  800  can further include one or more deflection feature of the golf club head  10 ,  100 ,  200 ,  300 ,  400 ,  500 ,  700 , and  1000  discussed above, including an insert, a thin uniform sole, or an optimized material, a reinforcement device, and/or thin face. 
     For exemplary purposes only, the dual density weight  880  can be located toward the heel end, toward the toe end, toward the top rail, toward the sole, toward the rear end, near the center of the club head, or any combination of the described locations. For example, the dual density weight  880  can be located toward the toe end and sole end, toward the heel end and sole end, toward the rear end and toe end sole, toward the top rail and heel end, toward the top rail and toe end, toward the sole near the center of the club head, or toward the top rail near the center of the club head. Further, the dual density weight  880  can be located on club head  10 ,  100 ,  200 ,  300 ,  400 ,  500 ,  700 , and  1000 . 
     Referring to  FIG. 18 , an embodiment of the dual density weight  880  welded to the golf club head  800  is displayed. The dual density weight  880  can include a base portion  881  and a shell portion  890 . The base portion  880  comprises a first surface  882  exposed to the exterior of the club head  800  and a second surface  882  opposite the first surface  881 . The shell portion  890  surrounds the exterior portion of the base portion  881 , such that the only portion of the dual density weight  880  in contact with the golf club head  800  is the shell portion  890 . In other words, the shell portion  890  spaces the base portion  881  from the golf club head  800 . In many embodiments, the shell portion  890  surrounds all surfaces of the base portion  881  except for the first surface  882 . In some embodiments, the shell portion  890  can surround the entire base portion  881  including the first side  882 . In other embodiments, the shell portion  890  can surround any portion of the base portion  881 , such that it creates a space between the base portion  881  and the golf club head  800 . 
     With continued reference to  FIG. 18 , the dual density weight  880  is welded to the golf club head  800  along the perimeter of the of the shell portion  890 . In the illustrated embodiment, the first surface  882  of the dual density weight  880  is flush with the exterior surface of the golf club head  800  when welded. In other embodiments, the dual density weight  800  may have an offset distance extending either outward or inward from the exterior surface of the golf club head  800 . The first surface  882  can comprise a curved or oblong first surface  882  to generally match the contour of the golf club head  800 . The first surface  882  can also comprise a flat first surface  882  extending between the weld points  895  and  896 . 
     In the illustrated embodiment, the base portion  881  comprises approximately 90% of the dual density weight  880  total volume, while the shell portion comprises approximately 10% of the dual density weight  880  total volume. In other embodiments, the base portion  881  can comprise approximately 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the dual density weights total volume. In the illustrated embodiment, the dual density weight  880  includes a rectangular cross-section. In other embodiments, the dual density weight  880  can include any cross-sectional shape, such as circular, triangular, polygonal or any other suitable shape. The dual density weight  880  can have a thickness “A” measured between the first weld spot  141  and the second weld spot  896 . In some constructions, the thickness “A” can be between 0.1 and 1.5 inches. In other embodiments, the thickness “A” can be between 0.1-0.4, 0.3-0.7, 0.6-1.0, 0.9-1.3, or 1.2-1.5 inches. For example, in some constructions, the thickness “A” can be 0.1 inch, 0.15 inch, 0.20 inch, 0.25 inch, 0.3 inch, 0.35 inch, 0.4 inch, 0.45 inch, 0.5 inch, 0.55 inch, 0.6 inch, 0.65 inch. 0.7 inch, 0.75 inch, 0.8 inch, 0.85 inch, 0.9 inch, 0.95 inch, 1.0 inch, 1.05 inch, 1.1 inch, 1,15 inch, 1.2 inch, 1.25 inch, 1.3 inch, 1.35 inch, 1.4 inch, 1.45 inch, or 1.5 inch. Further the dual density weight  880  can have a depth “B” measured between the first surface  882  and the second surface  883 . In some constructions, the depth “B” can be between 0.1 and 1.5 inches. In other embodiments, the depth “B” can be between 0.1-0.4, 0.3-0.7, 0.6-1.0, 0.9-1.3, or 1.2-1.5 inches. For example, in some constructions, the depth “B” can be 0.1 inch, 0.15 inch, 0.20 inch, 0.25 inch, 0.3 inch, 0.35 inch, 0.4 inch, 0.45 inch, 0.5 inch, 0.55 inch, 0.6 inch, 0.65 inch. 0.7 inch, 0.75 inch, 0.8 inch, 0.85 inch, 0.9 inch, 0.95 inch, 1.0 inch, 1.05 inch, 1.1 inch, 1,15 inch, 1.2 inch, 1.25 inch, 1.3 inch, 1.35 inch, 1.4 inch, 1.45 inch, or 1.5 inch. 
     The base portion  881  can comprise a first material, and the shell portion  890  can comprise a second material. The first material can comprise a high density material, while the second material can comprise a lower density material similar to the material of the golf club head. The base portion  881  and shell portion  890  of the dual density weight  880  can be formed integrally while the golf club head  800  can be formed separately. The dual density weight  880  can be welded to golf club head  800  along the perimeter of the shell portion  890  comprising the second material. The first material can comprise a high density metal, such as tungsten, tantalum, rhenium, osmium, iridium, or platinum, or other high density metals. The second material can comprise a material having a lower density than that of the first material. Further, the second material can comprise a material similar to the material of the golf club head  800 . 
     The dual density weight  880  can be utilized to redistribute the mass saved in the aforementioned deflection features. For example, any mass removed from the inserts  50 ,  150 ,  250 ,  350 , or  450 , the uniform thin sole  320 , the cutout  770 , or the optimized face material can be redistributed to the rear end of the club head  800  utilizing the dual density weight  880 . Redistributing the mass to the rear end  824  of the golf club head  800  aids in moving the CG low and back and therefore, increasing the MOI. 
     As discussed above, the golf club head  10  having deflection features can comprise one of or any combination of the above described features (insert, insert with voids, thin uniform sole, cutout in top rail, optimized face material, and/or dual density weight). Therefore, the golf club head  10  can comprise any combination of golf club heads  100 ,  200 ,  300 ,  400 ,  500 ,  700 ,  800 , and  100 . Further, the golf club head  10  comprising the deflection features can be a single unibody cast reducing the manufacturing costs. 
     Example 1 
     An exemplary golf club head  1000  comprising a reinforcement device  1112  having a looped rib was compared to a similar control club head, devoid of the reinforcement device using finite element analysis to simulate impact stresses. The reinforcement device  1112  of the exemplary club head  1000  includes a fillet between the outer perimeter of the reinforcement device and the rear surface of the face element, a face thickness that is thinner within the inner perimeter than without or outside the outer perimeter of the reinforcement device, and a rib span of 1.65 centimeters. Areas of high stress concentration on the exemplary club head  1000  discussed this example are indicated with reference number  1500  (see  FIGS. 30 and 33 ). Areas of high stress concentration on the control club heads discussed in this example are indicated with reference number  2000  (see  FIGS. 29, 31, and 32 ). 
     i. Fillet 
     The reinforcement element on the rear surface of the face element comprising a fillet between the outer perimeter of the reinforcement element and the rear surface of the face element, beneficially allows impact stresses to be transferred from the face element into the reinforcement element. 
     One of ordinary skill would expect the fillet between the outer perimeter of the reinforcement element and the rear surface of the face element to distribute impact stresses generally over a larger area at the interface between the face element and the reinforcement element. Upon impact with a golf ball, the fillet not only distributes stresses over a larger area at or near this interface, but also transfers stresses away from the interface, up and towards the end portion or rear end of the reinforcement element, away from the face element. 
     The transfer of stress at impact with a golf ball is illustrated in  FIGS. 29 and 30  for the club head  1000  having the reinforcement device  1112  compared to a control club head having a reinforcement element devoid of the fillet. Referring to  FIGS. 29A and 29B , at impact, areas of greatest stress  2000  are generated on the control club head at the interface of the reinforcement element with the face element and exhibit a familiar pattern associated with that of a stress concentrator at those locations.  FIGS. 30A and 30B  illustrate the efficient transfer of stress from the face element and into the end or rear portion of the reinforcement device, as a result of the fillet between the outer perimeter surface and the face element (particularly shown at the junction between the inner perimeter of the reinforcement device and the face element). 
     ii. Face Thickness 
     The transfer of impact stress away from the face element and into the reinforcement element allows the center of the face element to be thinned to increase face deflection and ball speed on impact with a golf ball. Accordingly, the face element can be thinner within the inner perimeter surface that without or outside the outer perimeter surface of the reinforcement element. Reduced face thickness allows greater bending at impact, thereby increasing energy transfer to a ball on impact to increase ball speed and travel distance. 
     Normally, reducing face thickness increases stress in the face element upon impact with a golf ball. The reduction in face thickness of the club head  1000  can be achieved without sacrificing durability (in fact, while reducing the stress on the face element), as a result of the reinforcement device. The efficient reduction in impact stress on the face element, while reducing the face element thickness within the inner perimeter of the reinforcement device relative to outside the outer perimeter of the reinforcement device results from the unique stress transfer properties of the fillet, as described above. 
     iii. Rib Span 
     The reinforcement device  1112  of the exemplary club head  1000  comprises a rib span of 1.65 centimeters. The rib span plays an important role in the amount of stress that is transferred from the face element into the end portion or rear end of the reinforcement device due to the fillet. Specifically, the rib span size allows the transfer of impact stress generated at the face into a hoop stress within the reinforcement device. 
       FIGS. 31-33  illustrate the transfer of stress at impact with a golf ball for the exemplary club head  1000  having reinforcement device  1112  compared to control club heads having a reinforcement element with a larger rib span and a smaller rib span than the exemplary club head  1000 . 
     Referring to  FIGS. 31A-31C , a control club head comprises a reinforcement device having a rib span of 2.54 centimeters, larger than the rib span of the reinforcement device of the exemplary club head  1000 . The rib span larger than the described rib span results in a large portion of the impact stress concentrating centrally on the front and rear of the face element, creating a stress riser on the face element. 
     Referring to  FIGS. 32A-32C , a control club head comprises a reinforcement device having a rib span of 0.51 centimeter, smaller than the rib span of the reinforcement device of the exemplary club head  1000 . The rib span smaller than the described rib span can result in a large portion of the impact stress concentrating on the front and rear of the face element around the perimeter of the reinforcement element, creating a stress rise on the face element. 
     Referring to  FIGS. 33A-33C , the exemplary club head having a rib span of 1.65 centimeters, corresponding to the impact area of a golf ball results in significant stresses being transferred away from the face element and into the reinforcement device, thereby reducing the stress on the face element. The low tensile stress observed on the rear surface of the face element, as illustrated in  FIGS. 33A-33C , having the described rib span and fillet, is an efficient stress distribution for a golf club/golf ball impact. 
     Replacement of one or more claimed elements constitutes reconstruction and not repair. Additionally, benefits, other advantages, and solutions to problems have been described with regard to specific embodiments. The benefits, advantages, solutions to problems, and any element or elements that may cause any benefit, advantage, or solution to occur or become more pronounced, however, are not to be construed as critical, required, or essential features or elements of any or all of the claims. 
     As the rules to golf may change from time to time (e.g., new regulations may be adopted or old rules may be eliminated or modified by golf standard organizations and/or governing bodies such as the United States Golf Association (USGA), the Royal and Ancient Golf Club of St. Andrews (R&amp;A), etc.), golf equipment related to the apparatus, methods, and articles of manufacture described herein may be conforming or non-conforming to the rules of golf at any particular time. Accordingly, golf equipment related to the apparatus, methods, and articles of manufacture described herein may be advertised, offered for sale, and/or sold as conforming or non-conforming golf equipment. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     While the above examples may be described in connection with an iron-type golf club, the apparatus and articles of manufacture described herein may be applicable to other types of golf club such as a driver type, a fairway wood-type golf club, a hybrid-type golf club, a wedge-type golf club, or a putter-type golf club. Alternatively, the apparatus and articles of manufacture described herein may be applicable other type of sports equipment such as a hockey stick, a tennis racket, a fishing pole, a ski pole, etc. 
     Moreover, embodiments and limitations disclosed herein are not dedicated to the public under the doctrine of dedication if the embodiments and/or limitations: (1) are not expressly claimed in the claims; and (2) are or are potentially equivalents of express elements and/or limitations in the claims under the doctrine of equivalents. 
     Various features and advantages of the disclosure are set forth in the following claims.