Patent Publication Number: US-2022226700-A1

Title: Golf club with coefficient of restitution feature

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/827,420, filed Mar. 23, 2020, which is a continuation of U.S. patent application Ser. No. 16/107,876, filed Aug. 21, 2018, now U.S. Pat. No. 10,646,756, which is a continuation of U.S. patent application Ser. No. 15/430,342, filed Feb. 10, 2017, now U.S. Pat. No. 10,080,934, which is a continuation of U.S. patent application Ser. No. 13/839,727, filed Mar. 15, 2013, now U.S. Pat. No. 9,662,545, all of which applications are incorporated by reference herein in their entirety. 
     This application references U.S. patent application Ser. No. 13/686,677 which is a continuation-in-part of U.S. patent application Ser. No. 13/340,039, filed Dec. 29, 2011, which is a continuation-in-part of U.S. patent application Ser. No. 13/166,668, filed Jun. 22, 2011, which is a continuation-in-part of U.S. patent application Ser. No. 12/646,769, filed Dec. 23, 2009, all of which applications are incorporated by reference herein in their entirety. Application Ser. No. 13/686,677 is also a continuation-in-part of U.S. patent application Ser. No. 13/305,533, filed Nov. 28, 2011, which is a continuation of U.S. patent application Ser. No. 12/687,003, filed Jan. 13, 2010, now U.S. Pat. No. 8,303,431, which claims the benefit of U.S. Provisional Patent Application No. 61/290,822, filed Dec. 29, 2009, all of which applications are incorporated herein by reference in their entirety. U.S. patent application Ser. No. 12/687,003 is also a continuation-in-part of U.S. patent application Ser. No. 12/474,973, filed May 29, 2009, which is a continuation in-part of U.S. patent application Ser. No. 12/346,747, filed Dec. 30, 2008, now U.S. Pat. No. 7,887,431, which claims the benefit of U.S. Provisional Patent Application No. 61/054,085, filed May 16, 2008, all of which applications are incorporated by reference herein in their entirety. 
     Additionally, this application references U.S. patent application Ser. No. 13/528,632, which is a continuation of U.S. patent application Ser. No. 13/224,222, filed Sep. 1, 2011, which is a continuation of U.S. patent application Ser. No. 12/346,752, filed Dec. 30, 2008, now U.S. Pat. No. 8,025,587, which claims the benefit of U.S. Provisional Application No. 61/054,085, filed May 16, 2008. Application Ser. Nos. 13/224,222, 12/346,752 and 61/054,085 are incorporated by reference herein in their entirety. 
     Additionally, this application references U.S. patent application Ser. No. 12/813,442, which is a continuation-in-part of U.S. patent application Ser. No. 12/006,060, filed Dec. 28, 2007, which is a continuation-in-part of U.S. patent application Ser. No. 11/863,198, filed Sep. 27, 2007, both of which are incorporated by reference herein in their entirety. 
     Additionally, this application references U.S. patent application Ser. No. 12/791,025, filed Jun. 1, 2010, and U.S. patent application Ser. No. 13/338,197, filed Dec. 27, 2011, which are incorporated by reference herein in their entirety. 
     Further, this application references U.S. patent application Ser. No. 10/290,817, filed Nov. 8, 2002, now U.S. Pat. No. 6,773,360, which is incorporated herein by reference in its entirety. Additionally, this application references U.S. patent application Ser. No. 11/647,797, filed Dec. 28, 2006, now U.S. Pat. No. 7,452,285, which is a continuation of U.S. patent application Ser. No. 10/785,692, filed Feb. 23, 2004, now U.S. Pat. No. 7,166,040, which is a continuation-in-part of U.S. patent application Ser. No. 10/290,817, cited previously, all of which are incorporated by reference herein in their entirety. This application also reference U.S. patent application Ser. No. 11/524,031, filed Sep. 19, 2006, which is a continuation-in-part of application Ser. No. 10/785,692, cited previously, both of which are incorporated by reference herein in their entirety. 
     Other patents and patent applications concerning golf clubs, including U.S. Pat. Nos. 7,407,447, 7,419,441, 7,513,296, and 7,753,806; U.S. Pat. Appl. Pub. Nos. 2004/0235584, 2005/0239575, 2010/0197424, and 2011/0312347; U.S. patent application Ser. Nos. 11/642,310, and 11/648,013; and U.S. Provisional Pat. Appl. No. 60/877,336 are incorporated by reference herein in their entireties. 
    
    
     FIELD 
     The current disclosure relates to golf club heads. More specifically, the current disclosure relates to golf club heads with features for improving playability, including at least one of relocation of center of gravity and coefficient of restitution features. 
     BACKGROUND 
     In the golf industry, club design often takes into consideration many design factors, including weight, weight distribution, spin rate, coefficient of restitution, characteristic time, volume, face area, sound, materials, construction techniques, durability, and many other considerations. Historically, club designers have been faced with performance trade-offs between design features that enhance one aspect of club performance while reducing at least one other aspect of club performance. For example, lighter weight can often lead to faster club speed, which often leads to greater distance; however, clubs that are too light weight can become uncontrollable by the user. In another example, thinner club faces often lead to distance gains, but thinning faces reduces durability in manufacture. Yet another example, high-tech materials may be used in various club designs to achieve performance results, but the gains may not justify the added costs of material acquisition and processing. The challenges of engineering modern golf clubs center largely around maximizing performance benefits while minimizing design trade-offs. 
     SUMMARY 
     A golf club head includes a face; a body, the body defining an interior and an exterior; the face and the body together defining a center of gravity, the center of gravity being proximate the face; a coefficient of restitution feature defined in the body; wherein the coefficient of restitution feature defines a gap in the body. A golf club head includes a face and a golf club body; the face and the golf club body defining a center of gravity, the center of gravity defined a distance, Δ z , from a ground plane as measured along a z-axis, the center of gravity defined a distance, CG y , from the center face along the y-axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and components of the following figures are illustrated to emphasize the general principles of the present disclosure. Corresponding features and components throughout the figures may be designated by matching reference characters for the sake of consistency and clarity. 
         FIG. 1A  is a toe side view of a golf club head in accord with one embodiment of the current disclosure. 
         FIG. 1B  is a face side view of the golf club head of  FIG. 1A . 
         FIG. 1C  is a perspective view of the golf club head of  FIG. 1A . 
         FIG. 1D  is a top view of the golf club head of  FIG. 1A . 
         FIG. 2  is a cross-sectional view of the golf club head taken in the plane indicated by line  2 - 2  of  FIG. 1D . 
         FIG. 3  is a detail view of detail  3  of  FIG. 2 . 
         FIG. 4  is a bottom view of the golf club head of  FIG. 1A . 
         FIG. 5  is a cross-sectional view of the golf club head taken in the plane indicated by line  5 - 5  of  FIG. 2 . 
         FIG. 6  is a cross-sectional view of the golf club head taken in the plane indicated by line  6 - 6  of  FIG. 2 . 
         FIG. 7  is a cross-sectional view of a golf club head in accord with one embodiment of the current disclosure as would be shown along the plane indicated by line  2 - 2  of  FIG. 1D . 
         FIG. 8  is a detail view of detail  8  of  FIG. 7 . 
         FIG. 9  is a cross-sectional view of the golf club head taken in the plane indicated by line  9 - 9  of  FIG. 7 . 
         FIG. 10  is a cross-sectional view of the golf club head taken in the plane indicated by line  10 - 10  of  FIG. 7 . 
         FIG. 11  is a cross-sectional view of a golf club head in accord with one embodiment of the current disclosure as would be shown along the plane indicated by line  2 - 2  of  FIG. 1D . 
         FIG. 12  is a detail view of detail  12  of  FIG. 11 . 
         FIG. 13  is a cross-sectional view of the golf club head taken in the plane indicated by line  13 - 13  of  FIG. 11 . 
         FIG. 14  is a cross-sectional view of the golf club head taken in the plane indicated by line  14 - 14  of  FIG. 11 . 
         FIG. 15  is a face side view of a golf club head of the current disclosure illustrating locations of COR testing. 
         FIG. 16A  is the detail view of  FIG. 8  including plugging material located in a coefficient of restitution feature in accord with one embodiment of the current disclosure. 
         FIG. 16B  is the detail view of  FIG. 12  including plugging material located in a coefficient of restitution feature in accord with one embodiment of the current disclosure. 
         FIG. 17A  is a toe side view of a golf club head in accord with one embodiment of the current disclosure. 
         FIG. 17B  is a face side view of the golf club head of  FIG. 17A . 
         FIG. 17C  is a perspective view of the golf club head of  FIG. 17A . 
         FIG. 17D  is a top view of the golf club head of  FIG. 17A . 
         FIG. 18  is a cross-sectional view of the golf club head taken in the plane indicated by line  18 - 18  in  FIG. 17D . 
         FIG. 19  is a detail view of detail  19  of  FIG. 18 . 
         FIG. 20  is a cross-sectional view of the golf club head taken in the plane indicated by line  20 - 20  of  FIG. 18 . 
         FIG. 21  is a bottom view of a golf club head in accord with one embodiment of the current disclosure. 
         FIG. 22  is a bottom view of a golf club head in accord with one embodiment of the current disclosure. 
         FIG. 23  is a cross-sectional view of a golf club head in accord with one embodiment of the current disclosure as would be shown along a plane taken in the reverse direction of view of the plane indicated by line  2 - 2  of  FIG. 1D . 
         FIG. 24  is a detail view of detail  24  of  FIG. 23 . 
         FIG. 25A  is a perspective view of detail  24  showing features of one embodiment of a coefficient of restitution feature in accord with one embodiment of the current disclosure. 
         FIG. 25B  is a perspective view of detail  24  showing features of one embodiment of a coefficient of restitution feature in accord with one embodiment of the current disclosure. 
         FIG. 26A  is a cutaway view of the coefficient of restitution feature of  FIG. 25A  as would be viewed in the plane indicated by line  26 - 26  in  FIG. 24 . 
         FIG. 26B  is a cutaway view of the coefficient of restitution feature of  FIG. 25B  as would be viewed in the plane indicated by line  26 - 26  in  FIG. 24 . 
         FIG. 27  is a perspective view of a golf club assembly in accord with one embodiment of the current disclosure including a golf club head in accord with one embodiment of the current disclosure. 
         FIG. 28A  is a toe side view of a golf club head in accord with one embodiment of the current disclosure. 
         FIG. 28B  is a face side view of the golf club head of  FIG. 28A . 
         FIG. 28C  is a perspective view of the golf club head of  FIG. 28A . 
         FIG. 28D  is a top view of the golf club head of  FIG. 28A . 
         FIG. 29  is a cross-sectional view of the golf club head taken in the plane indicated by line  29 - 29  of  FIG. 28B . 
         FIG. 30  is a detail view of detail  30  of  FIG. 29 . 
         FIG. 31  is a schematic diagram of a rigid beam. 
         FIG. 32  is a schematic diagram of a cantilever beam. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed is a golf club including a golf club head and associated methods, systems, devices, and various apparatus. It would be understood by one of skill in the art that the disclosed golf club is described in but a few exemplary embodiments among many. No particular terminology or description should be considered limiting on the disclosure or the scope of any claims issuing therefrom. For the sake of simplicity, standard unit abbreviations may be used, including but not limited to, “mm” for millimeters, “in.” for inches, “lb.” for pounds force, “mph” for miles per hour, and “rps” for revolutions per second, among others. 
     In the game of golf, when a player increases his or her distance with a given club, the result nearly always provides an advantage to the player. While golf club design aims to maximize the ability of a player to hit a golf ball as far as possible, the United States Golf Association—a rulemaking body in the game of golf—has provided a set rules to govern the game of golf. These rules are known as The Rules of Golf and are accompanied by various Decisions on The Rules of Golf. Many rules promulgated in The Rules of Golf affect play. Some of The Rules of Golf affect equipment, including rules designed to indicate when a club is or is not legal for play. Among the various rules are maximum and minimum limits for golf club head size, weight, dimensions, and various other features. For example, no golf club head may be larger than 460 cubic centimeters in volume. No golf club face may have a coefficient of restitution (COR) of greater than 0.830, wherein COR describes the efficiency of the golf club head&#39;s impact with a golf ball. 
     COR is a measure of collision efficiency. COR is the ratio of the velocity of separation to the velocity of approach. In this model, therefore, COR is determined using the following formula: 
     
       
         
           
             
               C 
               ⁢ 
               
                   
               
               ⁢ 
               O 
               ⁢ 
               
                   
               
               ⁢ 
               R 
             
             = 
             
               
                 ( 
                 
                   
                     v 
                     
                       club-post 
                     
                   
                   - 
                   
                     v 
                     
                       ball-post 
                     
                   
                 
                 ) 
               
               ÷ 
               
                 ( 
                 
                   
                     v 
                     
                       ball-pre 
                     
                   
                   - 
                   
                     v 
                     
                       club 
                       - 
                       pre 
                     
                   
                 
                 ) 
               
             
           
         
       
     
     where,
         v club-post  represents the velocity of the club after impact;   v ball-post  represents the velocity of the ball after impact;   v club-pre  represents the velocity of the club before impact (a value of zero for USGA COR conditions); and   v ball-pre  represents the velocity of the ball before impact.       

     Although the USGA specifies the limit for maximum COR, there is no specified region in which COR may be maximized. While multiple golf club heads have achieved the maximum 0.830 COR, the region in which such COR may be found has generally been limited—typically, in a region at a geometric center of the face of the golf club head or in a region of maximum COR that is in relatively small proximity thereto. Many golf club heads are designed to launch a golf ball as far as possible within The Rules of Golf when properly struck. However, even the greatest of professional golfers do not strike each and every shot perfectly. For the vast majority of golfers, perfectly struck golf shots are an exception if not a rarity. 
     There are several methods to address a particular golfer&#39;s inability to strike the shot purely. One method involves the use of increased Moment of Inertia (MOI). Increasing MOI prevents the loss of energy for strikes that do not impact the center of the face by reducing the ability of the golf club head to twist on off-center strikes. Particularly, most higher MOI designs focus on moving weight to the perimeter of the golf club head, which often includes moving a center of gravity of the golf club head back in the golf club head, toward a trailing edge. 
     Another method involves use of variable face thickness (VFT) technology. With VFT, the face of the golf club head is not a constant thickness across its entirety, but rather varies. For example, as described in U.S. patent application Ser. No. 12/813,442—which is incorporated herein by reference in its entirety—the thickness of the face varies in an arrangement with a dimension as measured from the center of the face. This allows the area of maximum COR to be increased as described in the reference. 
     While VFT is excellent technology, it can be difficult to implement in certain golf club designs. For example, in the design of fairway woods, the height of the face is often too small to implement a meaningful VFT design. Moreover, there are problems that VFT cannot solve. For example, because the edges of the typical golf club face are integrated (either through a welded construction or as a single piece), a strike that is close to an edge of the face necessarily results in poor COR. It is common for a golfer to strike the golf ball at a location on the golf club head other than the center of the face. Typical locations may be high on the face or low on the face for many golfers. Both situations result in reduced COR. However, particularly with low face strikes, COR decreases very quickly. In various embodiments, the COR for strikes 5 mm below center face may be 0.020 to 0.035 difference. Further off-center strikes may result in greater COR differences. 
     To combat the negative effects of off-center strikes, certain designs have been implemented. For example, as described in U.S. patent application Ser. No. 12/791,025 to Albertsen, et al., filed Jun. 1, 2010, and Ser. No. 13/338,197 to Beach, et al., filed Dec. 27, 2011—both of which are incorporated by reference herein in their entirety-coefficient of restitution features located in various locations of the golf club head provide advantages. In particular, for strikes low on the face of the golf club head, the coefficient of restitution features allow greater flexibility than would typically otherwise be seen from a region low on the face of the golf club head. In general, the low point on the face of the golf club head is not ductile and, although not entirely rigid, does not experience the COR that may be seen in the geometric center of the face. 
     Although coefficient of restitution features allow for greater flexibility, they can often be cumbersome to implement. For example, in the designs above, the coefficient of restitution features are placed in the body of the golf club head but proximal to the face. While the close proximity enhances the effectiveness of the coefficient of restitution features, it creates challenges from a design perspective. Manufacturing the coefficient of restitution features may be difficult in some embodiments. Particularly with respect to U.S. patent application Ser. No. 13/338,197, the coefficient of restitution feature includes a sharp corner at the vertical extent of the coefficient of restitution feature that experiences extremely high stress under impact conditions. It may become difficult to manufacture such features without compromising their structural integrity in use. Further, the coefficient of restitution features necessarily extend into the golf club body, thereby occupying space within the golf club head. The size and location of the coefficient of restitution features may make mass relocation difficult in various designs, particularly when it is desirous to locate mass in the region of the coefficient of restitution feature. 
     In particular, one challenge with current coefficient of restitution feature designs is the ability to locate the center of gravity (CG) of the golf club head proximal to the face. It has been desirous to locate the CG low in the golf club head, particularly in fairway wood type golf clubs. In certain types of heads, it may still be the most desirable design to locate the CG of the golf club head as low as possible regardless of its location within the golf club head. However, for reasons explained herein, it has unexpectedly been determined that a low and forward CG location may provide some benefits not seen in prior designs or in comparable designs without a low and forward CG. 
     For reference, within this disclosure, reference to a “fairway wood type golf club head” means any wood type golf club head intended to be used with or without a tee. For reference, “driver type golf club head” means any wood type golf club head intended to be used primarily with a tee. In general, fairway wood type golf club heads have lofts of 13 degrees or greater, and, more usually, 15 degrees or greater. In general, driver type golf club heads have lofts of 12 degrees or less, and, more usually, of 10.5 degrees or less. In general, fairway wood type golf club heads have a length from leading edge to trailing edge of 73-97 mm. Various definitions distinguish a fairway wood type golf club head form a hybrid type golf club head, which tends to resemble a fairway wood type golf club head but be of smaller length from leading edge to trailing edge. In general, hybrid type golf club heads are 38-73 mm in length from leading edge to trailing edge. Hybrid type golf club heads may also be distinguished from fairway wood type golf club heads by weight, by lie angle, by volume, and/or by shaft length. Fairway wood type golf club heads of the current disclosure are 16 degrees of loft. In various embodiments, fairway wood type golf club heads of the current disclosure may be from 15-19.5 degrees. In various embodiments, fairway wood type golf club heads of the current disclosure may be from 13-17 degrees. In various embodiments, fairway wood type golf club heads of the current disclosure may be from 13-19.5 degrees. In various embodiments, fairway wood type golf club heads of the current disclosure may be from 13-26 degrees. Driver type golf club heads of the current disclosure may be 12 degrees or less in various embodiments or 10.5 degrees or less in various embodiments. 
     One embodiment of a golf club head  100  is disclosed and described in with reference to  FIGS. 1A-1D . As seen in  FIG. 1A , the golf club head  100  includes a face  110 , a crown  120 , a sole  130 , a skirt  140 , and a hosel  150 . Major portions of the golf club head  100  not including the face  110  are considered to be the golf club body for the purposes of this disclosure. A coefficient of restitution feature (CORF)  300  is seen in the sole  130  of the golf club head  100 . 
     A three dimensional reference coordinate system  200  is shown. An origin  205  of the coordinate system  200  is located at the geometric center of the face (CF) of the golf club head  100 . See U.S.G.A. “Procedure for Measuring the Flexibility of a Golf Clubhead,” Revision 2.0, Mar. 25, 2005, for the methodology to measure the geometric center of the striking face of a golf club. The coordinate system  200  includes a z-axis  206 , a y-axis  207 , and an x-axis  208  (shown in  FIG. 1B ). Each axis  206 , 207 , 208  is orthogonal to each other axis  206 , 207 , 208 . The golf club head  100  includes a leading edge  170  and a trailing edge  180 . For the purposes of this disclosure, the leading edge  170  is defined by a curve, the curve being defined by a series of forwardmost points, each forwardmost point being defined as the point on the golf club head  100  that is most forward as measured parallel to the y-axis  207  for any cross-section taken parallel to the plane formed by the y-axis  207  and the z-axis  206 . The face  110  may include grooves or score lines in various embodiments. In various embodiments, the leading edge  170  may also be the edge at which the curvature of the particular section of the golf club head departs substantially from the roll and bulge radii. 
     As seen with reference to  FIG. 1B , the x-axis  208  is parallel to a ground plane (GP) onto which the golf club head  100  may be properly soled-arranged so that the sole  130  is in contact with the GP. The y-axis  207  is also parallel to the GP and is orthogonal to the x-axis  208 . The z-axis  206  is orthogonal to the x-axis  208 , the y-axis  207 , and the GP. The golf club head  100  includes a toe  185  and a heel  190 . The golf club head  100  includes a shaft axis (SA) defined along an axis of the hosel  150 . When assembled as a golf club, the golf club head  100  is connected to a golf club shaft (not shown). Typically, the golf club shaft is inserted into a shaft bore  245  defined in the hosel  150 . As such, the arrangement of the SA with respect to the golf club head  100  can define how the golf club head  100  is used. The SA is aligned at an angle  198  with respect to the GP. The angle  198  is known in the art as the lie angle (LA) of the golf club head  100 . An ground plane intersection point (GPIP) of the SA and the GP is shown for reference. In various embodiments, the GPIP may be used a point of reference from which features of the golf club head  100  may be measured or referenced. As shown with reference to  FIG. 1A , the SA is located away from the origin  205  such that the SA does not directly intersect the origin or any of the axes  206 , 207 , 208  in the current embodiment. In various embodiments, the SA may be arranged to intersect at least one axis  206 , 207 , 208  and/or the origin  205 . A z-axis ground plane intersection point  212  can be seen as the point that the z-axis intersects the GP. 
     As seen with reference to  FIG. 1C , the coefficient of restitution feature  300  (CORF) is shown defined in the sole  130  of the golf club head  100 . A modular weight port  240  is shown defined in the sole  130  for placement of removable weights. Various embodiments and systems of removable weights and their associated methods and apparatus are described in greater detail with reference to U.S. patent application Ser. Nos. 10/290,817, 11/647,797, 11/524,031, all of which are incorporated by reference herein in their entirety. The top view seen in  FIG. 1D  shows another view of the golf club head  100 . The shaft bore  245  can be seen defined in the hosel  150 . The cutting plane for  FIG. 2  can also be seen in  FIG. 1D . The cutting plane for  FIG. 2  coincides with the y-axis  207 . 
     Referring back to  FIG. 1A , a crown height  162  is shown and measured as the height from the GP to the highest point of the crown  120  as measured parallel to the z-axis  206 . In the current embodiment, the crown height  162  is about 36 mm. In various embodiments, the crown height  162  may be 34-40 mm. In various embodiments, the crown height may be 32-44 mm. In various embodiments, the crown height may be 30-50 mm. The golf club head  100  also has an effective face height  163  that is a height of the face  110  as measured parallel to the z-axis  206 . The effective face height  163  measures from a highest point on the face  110  to a lowest point on the face  110  proximate the leading edge  170 . A transition exists between the crown  120  and the face  110  such that the highest point on the face  110  may be slightly variant from one embodiment to another. In the current embodiment, the highest point on the face  110  and the lowest point on the face  110  are points at which the curvature of the face  110  deviates substantially from a roll radius. In some embodiments, the deviation characterizing such point may be a 10% change in the radius of curvature. In the current embodiment, the effective face height  163  is about 27.5 mm. In various embodiments, the effective face height  163  may be 2-7 mm less than the crown height  162 . In various embodiments, the effective face height  163  may be 2-12 mm less than the crown height  162 . An effective face position height  164  is a height from the GP to the lowest point on the face  110  as measured in the direction of the z-axis  206 . In the current embodiment, the effective face position height  164  is about 4 mm. In various embodiments, the effective face position height  164  may be 2-6 mm. In various embodiments, the effect face position height  164  may be 0-10 mm. A length  177  of the golf club head  177  as measured in the direction of the y-axis  207  is seen as well with reference to  FIG. 1A . In the current embodiment, the length  177  is about 85 mm. In various embodiments, the length  177  may be 80-90 mm. In various embodiments, the length  177  may be 73-97 mm. The distance  177  is a measurement of the length from the leading edge  170  to the trailing edge  180 . The distance  177  may be dependent on the loft of the golf club head in various embodiments. In one embodiment, the loft of the golf club head is about 15 degrees and the distance  177  is about 91.6 mm. In one embodiment, the loft of the golf club head is about 18 degrees and the distance  177  is about 87.4 mm. In one embodiment, the loft of the golf club head is about 21 degrees and the distance  177  is about 86.8 mm. 
     The cutaway view of  FIG. 2  shows the hollow nature of the golf club head  100 . The golf club head  100  of the current embodiment defines an interior  320  that is bounded by the portions of the golf club head  100  already discussed, including the face  110 , crown  120 , sole  130 , and skirt  140 , among other possible features that may provide a boundary to the interior. In the current embodiment, the modular weight port  240  provides access from any region exterior of the golf club head  100  to the interior  320 . One object among many of the current embodiment is to provide at least one of a low center of gravity and a forward center of gravity while maintaining a CORF  300 . In the current embodiment, a second weight pad portion  345  provides a region of increased mass low inside the golf club head  100 . Both a first weight pad portion  365  and the second weight pad portion  345  are portions of a weight pad  350  of the current embodiment. The weight pad  350  is integral with the golf club head  100  in the current embodiment. In various embodiments, the weight pad  350  may be of various materials and may be joined to the golf club head  350 . For example, in various embodiments, the weight pad  350  may be of tungsten, copper, lead, various alloys, and various other high density materials if a relocation of mass in the direction of the weight pad  350  is desired. If the weight pad  350  is a separate part joined to the golf club head  100 , the weight pad  350  may be joined to the golf club head  100  via welding, gluing, epoxy, mechanical fixing such as with fasteners or with key fit arrangements, or various other joining interfaces. In various embodiments, the weight pad  350  may be arranged on the inside or on the outside of the golf club head  100 . The first weight pad portion  365  extends a distance  286  in the direction of the y-axis  207 ; the second weight pad portion  345  extends a distance  288  in the direction of the y-axis  207 ; together, a length  290  defines the entirety of the weight pad  350  in the direction of the y-axis  207  and is about 55 mm. In various embodiments, the length  290  may be 50-60 mm. In various embodiments, the length  290  may be 45-62 mm. As seen, the weight pad  350  is offset from the leading edge  170  a distance  361 , as discussed in further detail below with reference to  FIG. 3 . In the current embodiment, the distance  361  is 5.3 mm, and in various embodiments it may be desired for the distance  361  to be as small as possible. In various embodiments, the distance  361  may be 4.5-6.5 mm. The second weight pad portion  345  is of a thickness  347  as measured in the direction of the z-axis. In the current embodiment, the thickness  347  is about 3.6 mm. In various embodiments, the thickness  347  may be 2-4 mm. In various embodiments, the thickness  347  may be up to 5 mm. An end  273  of the weight pad  350  is seen in the cutaway view (further detail seen in  FIG. 5 ). The end  273  is sloped for weight distribution and manufacturability. 
     For reference, a center line  214  that is parallel to the z-axis  206  is shown at the center of the CORF  300  in the view of  FIG. 2 . The location of the center line  214  is provided in greater detail below with reference to  FIG. 3 . A face-to-crown transition point  216  is also seen in the view. The face-to-crown transition point  216  is the point at which the face  110  stops and the crown  120  begins in a plane cut along the y-axis  207 , which is at the origin  205  in the current embodiment or, globally, at CF. It is understood that the face  110  and crown  120  transition along a curve, and the face-to-crown transition point  216  is located only in the plane of the y-axis  207  in the current embodiment, or, globally, in a plane intersecting CF under any coordinate system. Because of roll radius and bulge radius of the face  110 , the face-to-crown transition point  216  the transition between the face  110  and crown  120  is no closer to the origin  205  in any geometric space than at the face-to-crown transition point  216  in the current embodiment. Additionally, no part of the transition from face  110  to crown  120  is closer to the z-axis  206  as measured parallel to the y-axis  207 . As can be seen in the view of  FIG. 2 , the center line  214  is closer to the z-axis  206  at all points as measured parallel to the y-axis  207  than the face-to-crown transition point  216 . As such, no point of the transition between the face  110  and crown  120  is closer to the z-axis  206  than a center line passing through the center of the CORF  300  as measured parallel to the y-axis  207 , and, as such the CORF  300  is closer to the origin  205  (CF) than the transition of the face  110  to the crown  120  at any point in the current embodiment. It should be noted that, as loft of the golf club head  100  reduces, the face-to-crown transition point  206  may approach the center line  214 —for example, in driver-type golf club heads. However, the disclosure is accurate for the current embodiment and for all lofts of 13 degrees or greater. 
     Also seen in  FIG. 2 , a shaft plane z-axis  209  is seen. The shaft plane z-axis  209  is parallel to z-axis  206  but is in the same plane as the SA. For reference the view of  FIG. 6  shows the location of the shaft plane z-axis  209  in the same cutting plane as the SA. The shaft plane z-axis  209  is located a distance  241  from the z-axis  206  as measured in the direction of the y-axis  207 . In the current embodiment, the distance  241  is 13.25 mm. In various embodiments, the distance  241  may be 13-14 mm. In various embodiments, the distance  241  may be 10-17 mm. In various embodiments, the distance  241  may be as little as 1 mm and as large as 24 mm. In the current embodiment, the shaft plane z-axis  209  is located collinearly with a center of the modular weight port  240 . The location of the modular weight port  240  need not be correlated to the shaft plane z-axis  209  for all embodiments. 
     With returning reference to  FIG. 2 , in the current embodiment, the CORF  300  is defined in the sole  130  of the golf club head  100  such that the interior  320  of the golf club head  100  is not physically bounded by metal on all sides of the golf club head  100 . In the current embodiment, the CORF  300  is a through-slot, thereby being defined as an open region such that the interior  320  of the golf club head  100  is not separated from the exterior at the CORF  300 . The CORF  300  of the current embodiment decouples the face  110  from the sole  130 . Such a feature provides multiple unexpected advantages, as will be described in greater detail later in this disclosure. In various embodiments, the various features of the CORF  300  may include various shapes, sizes, and various embodiments to achieve desired results. In multiple embodiments, the golf club head  100  includes a face  110  that is fabricated separately and is secured to the golf club head  100  after fabrication. In the current embodiment, the face  110  is secured to the golf club head  100  by welding. Weld beads  262   a,b  are seen in the current embodiment. A tangent face plane  235  (TFP) can be seen in the profile view as well. The TFP  235  is a plane tangent to the face  110  at the origin  205  (at CF). The TFP  235  approximates a plane for the face  110 , even though the face  110  is curved at a roll radius and a bulge radius. The TFP  235  is angled at an angle  213  with respect to the z-axis  206 . The angle  213  in the current embodiment is the same as a loft angle of the golf club head as would be understood by one of ordinary skill in the art. For the current embodiment, the SA is entirely within a plane parallel to the plane formed by the x-axis  208  and the z-axis  206 . In some embodiments, the SA will not be in a plane parallel to the plane formed by the x-axis  208  and the z-axis  206 . In such embodiments, the shaft plane z-axis  209  will be a plane parallel to the plane formed by the x-axis  208  and the z-axis  206  and intersecting the GPIP. 
     A center of gravity  400  (CG) of the golf club head  100  is seen in  FIG. 2 . Because the weight pad  350  makes up a large portion of the mass of the golf club head  100 , the CG  400  is located relatively proximate the weight pad  350 . The distance of the CG  400  from the GP as measured in the direction of the z-axis  206  is seen and labeled as Δ z  in the current view. In the current embodiment, Δ z  is about 12 mm. In at least one embodiment, Δ z  is between 9 mm and 10 mm. In various embodiments, Δ z  may be 11-13 mm. In various embodiments, Δ z  may be 10-14 mm. In various embodiments, Δ z  may be 8-12 mm. In various embodiments, Δ z  may be 8-16 mm. Similarly, a distance labeled as A 1  is seen as the distance from the shaft plane z-axis  209  to the CG  400  as measured in the direction of the y-axis  207 . In the current embodiment, A 1  is about 11.5 mm. In various embodiments, A 1  may be between and including 11 mm and 13 mm. In various embodiments, A 1  may be between and including 10 mm and 14 mm. In various embodiments, A 1  may be between and including 8 mm and 16 mm. 
     The location of the CG  400  and the actual measurements of Δ z  and A 1  affect the playability of the golf club head  100 , as will be discussed below. A projection  405  of the CG  400  can be seen orthogonal to the TFP  235 . A projection point (not labeled in the current embodiment) is a point at which the projection  405  intersects the TFP  235 . In the current embodiment, the location of the CG  400  places the projection point at about the center of the face  110 , which is the location of the origin  205  (at CF) in the current embodiment. In various embodiments, the projection point may be in a location other than the origin  205  (at CF). 
     The location of the CG  400 —particularly the dimensions Δ z  and Δ 1 —affect the use of the golf club head  100 . Particularly with fairway wood type golf club heads similar to the golf club head  100 , small Δ z  has been used in various golf club head designs. Many designs have attempted to maximize Δ 1  within the parameters of the particular golf club head under design. Such a design may focus on MOI, as rearward movement of the CG can increase MOI in some designs. 
     However, there are several drawbacks to rearward CG location. One such drawback is dynamic lofting. Dynamic lofting occurs during the golf swing when the Δ 1  (for any club, Δ 1  is the distance from the shaft plane to the CG measured in the direction of the y-axis  207 ) is particularly large. Although the loft angle (seen in the current embodiment as angle  213 ) is static, when the Δ 1  is large, the CG of the golf club head is in position to cause the loft of the club head to increase during use. This occurs because, at impact, the offset CG of the golf club head from the shaft axis creates a moment of the golf club head about the x-axis  208  that causes rotation of the golf club head about the x-axis  208 . The larger Δ 1  becomes, the greater the moment arm to generate moment about the x-axis  208  becomes. Therefore, if Δ 1  is particularly large, greater rotation is seen of the golf club head about the x-axis  208 . The increased rotation leads to added loft at impact. 
     Dynamic lofting may be desired in some situations, and, as such, low and rearward CG may be a desired design element. However, dynamic lofting causes some negative effects on the resulting ball flight. First, for each degree of added dynamic loft, launch angle increases by 0.1°. Second, for each degree of added dynamic loft, spin rate increases by about 200-250 rpm. The increased spin rate is due to several factors. First, the dynamic lofting simply creates higher loft, and higher loft leads to more backspin. However, the second and more unexpected explanation is gear effect. The projection of a rearward CG onto the face of the golf club head creates a projection point above center face (center face being the ideal impact location for most golf club heads). Gear effect theory states that, when the projection point is offset from the strike location, the gear effect causes rotation of the golf ball toward the projection point. Because center face is an ideal impact location for most golf club heads, offsetting the projection point from the center face can cause a gear effect on perfectly struck shots. Particularly with rearward CG fairway woods, loft of the golf club head causes the projection point to be above the center face—or, above the ideal strike location. This results in a gear effect on center strikes that causes the ball to rotate up the face of the golf club head, generating even greater backspin. Backspin may be problematic in some designs because the ball flight will “balloon”—or, in other words, rise too quickly—and the distance of travel of the resultant golf shot will be shorter than for optimal spin conditions. A third problem with dynamic lofting is that, in extreme cases, the trailing edge of the golf club head may contact the ground, causing poor golf shots; similarly, the leading edge may raise off the ground, causing thin golf shots. 
     A further consideration with offsetting the CG such that the projection point is not aligned with center face is the potential loss of energy due to spin. Because of the aforementioned gear effect problem, moving the projection point anywhere other than the ideal strike location reduces the energy transfer on ideal strikes, as more energy is turned into spin. As such, golf club heads for which the projection point is offset from the ideal strike location may experience less distance on a given shot than golf club heads for which the projection point is aligned with the ideal strike location (assumed to be at center face). 
     As stated previously, in some embodiments, the events described above are desired outcomes of the design process. In the current embodiment, the location of the CG  400  creates a projection point (not labeled) that is closely aligned to the CF (at the origin  205 ). 
     As can be seen, the golf club head  100  of the current embodiment is designed to produce a small Δ z  and, thereby, to have a relatively low CG  400 . In various embodiments, however, the size of Δ 1  may become more important to the goal to achieve ideal playing conditions for a given set of design considerations. 
     A measurement of the location of the CG from the origin  205  (CF) along the y-axis  207 —termed CG y  distance—is a sum of Δ 1  and the distance  241  between the z-axis  206  and the shaft plane z-axis  209 . In the current embodiment of the golf club head  100 , distance  241  is nominally 13.25 mm, and Δ 1  is nominally 11.5 mm, although variations on the CG y  distance are described herein. In the current embodiment, the CG y  distance is 24.75 mm, although in various embodiments of the golf club head  100  the CG y  distance may be as little as 28 mm and as large as 32 mm. 
     Knowing the CG y  distance allows the use of a CG effectiveness product to describe the location of the CG in relation to the golf club head space. The CG effectiveness product is a measure of the effectiveness of locating the CG low and forward in the golf club head. The CG effectiveness product (CG eff ) is calculated with the following formula and, in the current embodiment, is measured in units of the square of distance (mm 2 ): 
     
       
         
           
             
               C 
               ⁢ 
               
                 G 
                 eff 
               
             
             = 
             
               C 
               ⁢ 
               
                 G 
                 y 
               
               × 
               
                 Δ 
                 z 
               
             
           
         
       
     
     With this formula, the smaller the CG eff , the more effective the club head is at relocating mass low and forward. This measurement adequately describes the location of the CG within the golf club head without projecting the CG onto the face. As such, it allows for the comparison of golf club heads that may have different lofts, different face heights, and different locations of the CF. For the current embodiment, CG y  is 24.75 mm and Δ z  is about 12 mm. As such, the CG eff  of the current embodiment is about 297 mm 2 . In various embodiments, CG eff  is below 300 mm 2 , as will be shown elsewhere in this disclosure. In various embodiments, CG eff  of the current embodiments is below 310 mm 2 . In various embodiments, CG eff  of the current embodiments is below 315 mm 2 . In various embodiments, CG eff  of the current embodiments is below 325 mm 2 . Further, CG y  distance informs the distance of the CG to the face as measured orthogonally to the TFP  235 . The distance to the CG measured orthogonally to the TFP  235  is the distance of the projection  405 . For any loft θ of the golf club head (which is the same as angle  213  for the current embodiment), the distance of the golf club face to the CG (D CG ) as measured orthogonally to the TFP  235  is described by the equation below: 
     
       
         
           
             
               D 
               
                 C 
                 ⁢ 
                 G 
               
             
             = 
             
               C 
               ⁢ 
               
                 G 
                 y 
               
               × 
               
                 cos 
                 ⁡ 
                 
                   ( 
                   θ 
                   ) 
                 
               
             
           
         
       
     
     For the current embodiment, a loft of 15 degrees and CG y  of 24.75 mm means the D CG  is about 23.9 mm. In various embodiments, D CG  may be 20-25 mm. In various embodiments, D CG  may be 15-30 mm. In various embodiments, D CG  may be less than 35 mm. In various embodiments, D CG  may be governed by its relationship to previously determined CG y , Δ 1 , Δ z , or some other physical aspect of the golf club head  100 . 
     The CORF  300  of the current embodiment is defined proximate the leading edge  170  of the golf club head  100 , as seen with reference to  FIG. 3 . As previously discussed, the CORF  300  of the current embodiment is a through-slot providing a port from the exterior of the golf club head  100  to the interior  320 . The CORF  300  is defined on one side by a first sole portion  355 . The first sole portion  355  extends from a region proximate the face  110  to the sole  130  at an angle  357 , which is acute in the current embodiment. In various embodiments, the first sole portion  355  is coplanar with the sole  130 ; however, it is not coplanar in the current embodiment. In the current embodiment, the angle  357  is about 88 degrees. In various embodiments, the angle  357  may be 85-90 degrees. In various embodiments, the angle  357  may be 82-92 degrees. The first sole portion  355  extends from the face  110  a distance  359  of about 5.6 mm as measured orthogonal to the TFP  235 . In various embodiments, the distance  359  may be 5-6 mm. In various embodiments, the distance  359  may be 4-7 mm. In various embodiments, the distance  359  may be up to 12.5 mm. The first sole portion  355  projects along the y-axis  207  the distance  361  as measured to the leading edge  170 , which is the same distance that the weight pad  350  is offset from the leading edge  170 . In the current embodiment, the distance  361  is about 5 mm. In various embodiments, the distance  361  is 4.5-5.5 mm. In various embodiments, the distance  361  is 3-7 mm. In various embodiments, the distance  361  may be up to 10 mm. In the current embodiment, the distances  359 , 361  are measured at the cutting plane, which is coincident with the y-axis  207  and z-axis  206 . In various embodiments, measurements—including angles and distances such as distances  359 , 361 —may vary depending on the location where measured and as based upon the shape of the CORF  300 . 
     The CORF  300  is defined over a distance  370  from the first sole portion  355  to the first weight pad portion  365  as measured along the y-axis. In the current embodiment, the distance  370  is about 3.0 mm. In various embodiments, the distance  370  may be larger or smaller. In various embodiments, the distance  370  may be 2.0-5.0 mm. In various embodiments, the distance  370  may be variable along the CORF  300 . It would be understood by one of skill in the art that, in various embodiments, the first sole portion  355  may extend in a location for which no rearward vertical surface  385   b  is immediately adjacent and, as such, the distance  370  may become large if measured along the y-axis  207 . As previously discussed, the center line  214  passes through the center of the CORF  300 . The center of the CORF  300  is defined by a distance  366 , which is exactly one half the distance  370 . In the current embodiment, the distance  366  is 1.5 mm. 
     The CORF  300  is defined distal the leading edge  170  by the first weight pad portion  365 . The first weight pad portion  365  in the current embodiment includes various features to address the CORF  300  as well as the modular weight port  240  defined in the first weight pad portion  365 . In various embodiments, the first weight pad portion  365  may be various shapes and sizes depending upon the specific results desired. In the current embodiment, the first weight pad portion  365  includes an overhang portion  367  over the CORF  300  along the y-axis  207 . The overhang portion  367  includes any portion of the weight pad  350  that overhangs the CORF  300 . For the entirety of the disclosure, overhang portions include any portion of weight pads overhanging the CORFs of the current disclosure. The overhang portion  367  includes a faceward most point  381  that is the point of the overhang portion  367  furthest toward the leading edge  170  as measured in the direction of the y-axis  207 . 
     The overhang portion  367  overhangs a distance that is about the same as the distance  370  of the CORF  300  in the current embodiment. In the current embodiment, the weight pad  350  (including the first weight pad portion  365  and the second weight pad portion  345 ) are designed to provide the lowest possible center of gravity of the golf club head  100 . A thickness  372  of the overhang portion  367  is shown as measured in the direction of the z-axis  206 . The thickness  372  may determine how mass is distributed throughout the golf club head  100  to achieve desired center of gravity location. The overhang portion  367  includes a sloped end  374  that is about parallel to the face  110  (or, more appropriately, to the TFP  235 , not shown in the current view) in the current embodiment, although the sloped end  374  need not be parallel to the face  110  in all embodiments. A separation distance  376  is shown as the distance between an inner surface  112  of the face  110  and the sloped end  374  as measured orthogonally to the TFP  235 . In the current embodiment, the separation distance  376  of about 4.5 mm is seen as the distance between the inner surface  112  of the face  110  and the sloped end  374  of the overhang portion  367  as measured orthogonal to the TFP  235 . In various embodiments, the separation distance  376  may be 4-5 mm. In various embodiments, the separation distance  376  may be 3-6 mm. The CORF  300  includes a beveled edge  375  (shown as  375   a  and  375   b  in the current view). In the current embodiment, the beveled edge  375  provides some stress reduction function, as will be described in more detail later. In various embodiments, the distance that the overhang portion  367  overhangs the CORF  300  may be smaller or larger, depending upon the desired characteristics of the design. 
     As can be seen, an inside surface  382  of the first sole portion  355  extends downward toward the sole  130 . The inside surface  382  terminates at a low point  384 . The CORF  300  includes a vertical surface  385  (shown as  385   a,b  in the current view) that defines the edges of the CORF  300 . The CORF  300  also includes a termination surface  390  that is defined along a lower surface of the overhang portion  367 . The termination surface  390  is offset a distance  392  from the low point  384  of the inside surface  382 . The offset distance  392  provides clearance for movement of the first sole portion  355 , which may deform in use, thereby reducing the distance  370  of the CORF  300 . Because of the offset distance  392 , the vertical surface  385  is not the same for vertical surface  385   a  and vertical surface  385   b . However, the vertical surface  385  is continuous around the CORF  300 . In the current embodiment, the offset distance  392  is about 0.9 mm. In various embodiments, the offset distance  392  may be 0.2-2.0 mm. In various embodiments, the offset distance  392  may be up to 4 mm. An offset to ground distance  393  is also seen as the distance between the low point  384  and the GP. The offset to ground distance  393  is about 2.25 mm in the current embodiment. The offset to ground distance  393  may be 2-3 mm in various embodiments. The offset to ground distance  393  may be up to 5 mm in various embodiments. A rearward vertical surface height  394  describes the height of the vertical surface  385   b  and a forward vertical surface height  396  describes the height of the vertical surface  385   a . In the current embodiment, the forward vertical surface height  396  is about 0.9 mm and the rearward vertical surface height  394  is about 2.2 mm. In various embodiments, the forward vertical surface height  396  may be 0.5-2.0 mm. In various embodiments, the rearward vertical surface height  394  may be 1.5-3.5 mm. A termination surface to ground distance  397  is also seen and is about 3.2 mm in the current embodiment. The termination surface to ground distance  397  may be 2.0-5.0 mm in various embodiments. The termination surface to ground distance  397  may be up to 10 mm in various embodiments. 
     In various embodiments, the vertical surface  385   b  may transition into the termination surface  390  via fillet, radius, bevel, or other transition. One of skill in the art would understand that, in various embodiments, sharp corners may not be easy to manufacture. In various embodiments, advantages may be seen from transitions between the vertical surface  385  and the termination surface  390 . Relationships between these surfaces ( 385 ,  390 ) are intended to encompass these ideas in addition to the current embodiments, and one of skill in the art would understand that features such as fillets, radii, bevels, and other transitions may be substantially fall within such relationships. For the sake of simplicity, relationships between such surfaces shall be treated as if such features did not exist, and measurements taken for the sake of relationships need not include a surface that is fully vertical or horizontal in any given embodiment. 
     The thickness  372  of the overhang portion  567  of the current embodiment can be seen. The thickness  372  in the current embodiment is about 3.4 mm. In various embodiments, the thickness  372  may be 3-5 mm. In various embodiments, the thickness  372  may be 2-10 mm. As shown with relation to other embodiments of the current disclosure, the thickness  372  maybe greater if combined with features of those embodiments. Additionally, the rearward vertical surface height  394  defines the distance of the CORF  300  from the termination of the bevel  375  to the termination surface  390  as well as the distance of the vertical surface  385   b , although such a relationship is not necessary in all embodiments. As can be seen, each of the offset distance  392 , the offset to ground distance  393 , and the vertical surface height  394  is less than the thickness  372 . As such, a ratio of each of the offset distance  392 , the offset to ground distance  393 , and the vertical surface height  394  to the thickness  372  is less than or equal to 1. In various embodiments, the CORF  300  may be characterized in terms of the termination surface to ground distance  397 . For the current embodiment, a ratio of the termination surface to ground distance  397  as compared to the thickness  372  is about 1, although it may be less in various embodiments. For the sake of this disclosure, the ratio of termination surface to ground distance  397  as compared to the thickness  372  is termed the “CORF mass density ratio.” While the CORF mass density ratio provides one potential characterization of the CORF, it should be noted that all ratios cited in this paragraph and throughout this disclosure with relation to dimensions of the various weight pads and CORFs may be utilized to characterize various aspects of the CORFs, including mass density, physical location of features, and potential manufacturability. In particular, the CORF mass density ratio and other ratios herein at least provide a method of describing the effectiveness of relocating mass to the area of the CORF, among other benefits. 
     The CORF  300  may also be characterized in terms of distance  370 . A ratio of the offset distance  392  as compared to the distance  370  is about equal to 1 in the current embodiment and may be less than 1 in various embodiments. 
     In various embodiments, the CORF  300  may be plugged with a plugging material (not shown). Because the CORF  300  of the current embodiment is a through-slot (providing a void in the golf club body), it is advantageous to fill the CORF  300  with a plugging material to prevent introduction of debris into the CORF  300  and to provide separation between the interior  320  and the exterior of the golf club head  100 . Additionally, the plugging material may be chosen to reduce or eliminate unwanted vibrations, sounds, or other negative effects that may be associated with a through-slot. The plugging material may be various materials in various embodiments depending upon the desired performance. In the current embodiment, the plugging material is polyurethane, although various relatively low modulus materials may be used, including elastomeric rubber, polymer, various rubbers, foams, and fillers. The plugging material should not substantially prevent deformation of the golf club head  100  when in use (as will be discussed in more detail later). 
     The CORF  300  is shown in the view of  FIG. 4 . The CORF  300  of the current embodiment includes multiple portions that define its shape. The CORF  300  includes a central portion  422  that comprises a plurality of the CORF  300 . The central portion  422  is relatively straight as compared to other portions of the CORF  300 . In the current embodiment, the central portion  422  is a curve of a radius of about 100 mm. A profile of the central portion  422  approximately follows the profile of the leading edge  170  such that the curvature of the central portion  422  does not substantially deviate from a curvature of the leading edge  170 . The distance  370  can be seen as the defining width of the CORF  300 . The defining width is measured orthogonally to the vertical surface  385  such that the defining width is not necessarily at a constant angle with respect to any axis (x-axis  208 , y-axis  207 , z-axis  206 ). The CORF  300  includes two additional portions. A heelward return portion  424  and a toeward return portion  426  are seen. The heelward return portion  424  and toeward return portion  426  diverge from the leading edge  170  such that a curvature of the CORF  300  in the region of the heelward return portion  424  and the toeward return portion  426  is not substantially the same as the curvature of the leading edge  170 . In the current embodiment, the defining width of the CORF  300  remains constant such that the distance  370  defines the defining width of the CORF  300  throughout all portions (central portion  422 , heelward return portion  424 , toeward return portion  426 ). In various embodiments, the defining width of at least one of the heelward return portion  424  and the toeward return portion  426  may be variable with respect to the defining with of the central portion  422 . In the current embodiment, the divergence of the heelward return portion  424  and the toeward return portion  426  from the leading edge  170  provides additional stress reduction to avoid potential failure—such as cracking or permanent deformation—of the golf club head  100  along the CORF  300 . In the current embodiment, the heelward return portion  424 , central portion  422 , and toeward return portion  426  are not constant radius between the three portions. Instead, the CORF  300  of the current embodiment is a multiple radius (hereinafter “MR”) CORF  300 . Because of the arrangement of the view of  FIG. 4 , the termination surface  390  can be seen under the CORF  300 . 
     The CORF  300  includes a heelward end  434  and a toeward end  436 . Each end  434 , 436  of the CORF  300  is identified at the end of the beveled edge  375 . In various embodiments, the beveled edge  375  may be omitted, and the ends  434 , 436  may be closer together as a result. A distance  452  is shown between the toeward end  436  and the heelward end  434  as measured in the direction of the x-axis  208 . In the current embodiment, the distance  452  is 40-43 mm. In various embodiments, the distance  452  may be 33-50 mm. In various embodiments, the distance  452  may be larger or smaller than the ranges cited herein and is limited only by the size of the golf club head. The CORF  300  includes a distance  454  as measured in the direction of the y-axis  207 . In the current embodiment, the distance  454  is 9-10 mm. In various embodiments, the distance  454  may be 7-12 mm. In various embodiments, the distance  454  may be larger or smaller than ranges cited herein and is limited only by the size of the golf club head. 
     As seen with reference to  FIG. 5 , the CORF  300  of the current embodiment is reinforced along its ends  434 , 436  and with various features. The CORF  300  is subject to cracking under high stress. A heel stress relief pad  484  and a toe stress relief pad  486  are included along the interior  320  at the CORF  300 . In particular, the stress relief pads  484 , 486  are regions of relatively thick construction along ends  434 , 436  of the CORF  300 . The stress relief pads  484 , 486  may also aid in flow of material during casting, as the increased thickness of the material at the ends  434 , 436  may help define those regions of the CORF  300  that experience the greatest stresses in use. A thickness transition region  492  is seen both in the cutaway view and in cross-sectional view of the toe  185 . The thickness transition region  492  provides a step up in thickness of walls of the golf club head  100  proximate the face  110 . The increased thickness provides multiple benefits, including relocation of mass close to the face  110  and increased structural integrity in the region of the face  110 , among others. As can be seen in the view of  FIG. 5 , the overhang portion  367  generally follows the profile of the CORF  300 , which includes the central portion  422 , the heelward return portion  424 , and the toeward return portion  426  (see  FIG. 4 ). As can be seen, the overhang portion  367  of the current embodiment includes at least two reinforcement sections  494 , 496  wherein the thickness of the overhang portion  367  is variable. The reinforcement sections  494 , 496  provide similar benefits to the stress relief pads  484 , 486 , including better stress relief, mold flow, and movement of mass. A dimension  271  of the weight pad  350  is seen as the largest length of the weight pad  350  as measured along the x-axis  208 , and the dimension  271  is about 63 mm in the current embodiment. The dimensions  271  may be 60-70 mm in various embodiments. The dimension  271  may be 50-75 mm in various embodiments. The weight pad  350  of the current embodiment extends to its edges where it contacts the skirt  140 . A further view of the golf club head  100  is seen in  FIG. 6 . Various stress relief pads and reinforcements of the current disclosure may be replaced with similar features in various embodiments, including ribs, changes in thickness, or dimension changes, among other methods. One of skill in the art would understand that such alternative features are intended to be encompassed by the scope of this disclosure. 
     As previously mentioned, coefficient of restitution features such as CORF  300  and previously cited embodiments provide multiple benefits, particularly in a fairway wood type golf club head. In general, coefficient of restitution features provide benefits that would otherwise be unavailable in a fairway wood type golf club head. 
     For example, fairway woods with coefficient of restitution features are capable of seeing higher COR than non-CORF fairway woods. Multiple reasons exist for this. In the embodiment of CORF  300  in golf club head  100 , a strike of a golf ball on the center of the face experiences—as with most wood-type golf club heads—maximum COR. As shown, a golf club head with a coefficient of restitution feature such as CORF  300  becomes unconstrained in the plane of the center face in at least the direction of impact, thereby allowing an increase in COR. 
     At impact, the golf club head  100  may experience normal forces of greater than 1 ton (2,000 pounds) concentrated in the location of impact—ideally, center face. Under such force, the metals with which most golf club heads are made experience at least some deflection, which results in a measurable COR. If a golf club face is as rigid as possible, any deflection will be minimal, and the amount of energy stored as potential spring energy is minimal as well. With minimal deflection, the face does not return to its typical position with a great amount of energy, and, thus, does not impart additional energy onto the golf ball. 
     In some designs, it may be possible to make a golf club head with advanced materials and with thinner faces. Materials may include 6-4 titanium, 15-3-3-3 titanium, and steels of strength greater than 1400 MPa, among others. A thinner face will often result in a higher COR because the bending stiffness of the face is a function of thickness. However, designers run a risk in making golf club faces too thin, as cracking or other failure may occur if the golf club face becomes too thin. 
     In driver-type golf club heads, many golf club heads have maximized the USGA size limit of 460 cubic centimeters in volume. Many drivers have faces with relatively large surface area resulting from relatively large face height and relatively large face width. Accordingly, many drivers are able to achieve the USGA maximum 0.830 COR, as described previously, because the large area of the face makes it possible to spread deflection of greater distances. Cumulatively, small deflections in the face result in a large deflection upon center face hits, leading to greater restitution, even when driver-type golf club heads are manufactured with less thin faces than would be required to achieve the same COR in a smaller face. In fact, many driver-type golf club heads—for example, as in U.S. patent application Ser. No. 12/813,442, as previously referenced and incorporated herein by reference in its entirety—are designed with variable face thickness (VFT) to increase the area of the face for which COR is maximized. As such, variability in distance for off-center hits is reduced, leading to a larger COR area. 
     Conversely, in fairway wood type golf club heads, it is often difficult to reach maximum COR even on center face strikes. Fairway wood type golf club heads typically include much smaller face area, much smaller face height, and much smaller face width than driver type golf club heads. To maximize COR on fairway wood type golf club heads, many designs decrease face thickness, and, in doing so, often compromise structural integrity of the face of the golf club head. Additionally, the joints at the edges of the face between the face and the club body are often more rigid than in the center of the face, leading to widely varying distances between center-face strikes and off-center strikes, even on driver-type golf club heads. Coefficient of restitution features as described in references cited herein provide some benefit but are still largely constrained. Further, the geometric space occupied within the golf club head by protruding coefficient of restitution features prevents relocation of mass, as previously discussed. 
     The embodiments of the current disclosure address the challenges that previous designs were unable to address. Because the CORF  300  and other CORFs of the current disclosure (as described with reference to other embodiments of the current disclosure below) do include physical elements occupying space in the interior  320  of the golf club head  100  or other golf club heads of the current disclosure, it becomes possible to relocate mass in a region proximate the CORF  300  and other CORFs of the current disclosure—particularly, in the low and forward region—in various embodiments of the golf club heads of the current disclosure. Such relocation of mass allows maximum design flexibility to provide optimal playing conditions based on the desired CG location of the club designer. 
     Because the CORF  300  and other CORFs of the current disclosure are not physically coupled at the leading edge  170  to the sole  130  for at least a region proximate the center of the face, leading to greater deflection and, thereby, greater COR. Elementary beam theory explains how this is possible. 
     For illustration, a traditional golf club head having a face connected to the golf club body at all ends can be approximated by a rigid beam supported at its ends, as shown in  FIG. 31 . 
     For the supported beam above with rigid supports along its ends, deflection δ at the point of application of force P is found using the equation below where L is the length of the beam, E is the elastic modulus of the material of the beam, and I is the area moment of inertia of the beam: 
     
       
         
           
             δ 
             = 
             
               
                 P 
                 ⁢ 
                 
                   L 
                   3 
                 
               
               
                 4 
                 ⁢ 
                 8 
                 ⁢ 
                 E 
                 ⁢ 
                 I 
               
             
           
         
       
     
     A golf club head such as golf club head  100  including a coefficient of restitution feature such as CORF  300  and other CORFs of the current disclosure can be approximated by a cantilever beam for the sake of illustration, as shown in  FIG. 32 . 
     The deflection at the point of application of force P is as described in the equation below: 
     
       
         
           
             δ 
             = 
             
               
                 P 
                 ⁢ 
                 
                   L 
                   3 
                 
               
               
                 2 
                 ⁢ 
                 4 
                 ⁢ 
                 E 
                 ⁢ 
                 I 
               
             
           
         
       
     
     As such, with all other variables being equal, the deflection at the center point of a cantilever beam is twice that of an end-supported beam. This relationship illustrates the value of coefficient of restitution features such as CORF  300  and other CORFs of the current disclosure in allowing greater deflection at the center of the face. 
     However, there is additional benefit to CORF  300  and other CORFs of the current disclosure not seen in simple beam theory. As previously mentioned, even the greatest golfers do not strike the golf ball perfectly on every golf shot. As seen in particular detail with reference to  FIG. 3 , the leading edge of most golf club heads includes an angle that is acute—in the current embodiment, leading edge  170  includes angle  357 . Because of the angle  357  is acute, material in the region proximate the angle  357  is particularly less flexible. As such, shots hit “thin”—or, low on the face of a traditional golf club head—experience particularly poor distance because the COR difference between thin shots and shots struck center face is particularly great. In the embodiments of the current disclosure, the CORF  300  and other CORFs of the current disclosure allow the usually-rigid leading edge  170  to have greater flexibility than would otherwise be seen, allowing the COR for thin shots to be much closer to the COR for center face strikes than would be seen for a typical golf club head. 
     Another embodiment of a golf club head  500  is seen in cross-sectional view in  FIG. 7 . The cross-sectional view of  FIG. 7  is taken along the same plane for the golf club head  500  as was  FIG. 2  for the golf club head  100 . The golf club head  500  is substantially similar to the golf club head  100  in many ways. For the sake of simplicity of the disclosure, where features are similarly drawn and/or identified with common reference identifiers, one of skill in the art would understand that the features of one embodiment may be included in another embodiment where the inclusion of such features would not contradict other elements of the disclosure. Even where reference identifiers are not included in the several exemplary embodiments described herein, one of skill in the art would understand that similarly drawn features are intended to be consistent amongst the several embodiments except wherein the disclosure contradicts such assumption or for which such assumption would be antithetical so some explicit disclosure. 
     The golf club head  500  is similar in shape and features to the golf club head  100 . A weight pad  550  of the golf club head  500  is more compacted to the low and forward location in the golf club head  500  than the weight pad  350  of the golf club head  100 . In the current embodiment, the weight pad  550  includes a thickness  547  of about 9.5 mm. In various embodiments, the thickness  547  may be 8-10 mm. In various embodiments, the thickness  547  may be 6-12 mm. The thickness  547  in the current embodiment is greater than the thickness  347 . However, a length  590  of the weight pad  550  is about 26.5 mm and is smaller than the length  290  of weight pad  350 . In various embodiments, the length  590  may be 24-30 mm. In various embodiments, the length  590  may be 21-33 mm. A CORF  800  can be seen and is substantially similar to CORF  300 . An end  573  of the weight pad  550  is seen in the cutaway view (further detail seen in  FIG. 9 ). The end  573  is sloped for weight distribution and manufacturability. 
     One noted difference, among at least several differences, is that the golf club head  500  is designed to locate the CG  600  of the current embodiment in a location that is low and forward in the golf club head. Δ z  for golf club head  500  is about 12.9 mm. In various embodiments, Δ z  may be 11-13 mm. In various embodiments, Δ z  may be 10-13.5 mm. In various embodiments, Δ z  may be up to 14.5 mm. Δ 1  for golf club head  500  is about 7 mm. In various embodiments, Δ 1  may be 6.5-7.5 mm. In various embodiments, Δ 1  may be 6-11 mm. In various embodiments, Δ 1  may be up to 12 mm. As comparing Δ 1  for the golf club head  100  to Δ 1  for the golf club head  500 , it can be noted that Δ 1  is smaller for the golf club head  500  than for the golf club head  100 . Although Δ z  is larger for the golf club head  500  than for the golf club head  100 , the difference is not substantial. 
     As can be seen, a projection  505  of the CG  600  onto the face  110  results in a projection point  510  that is notably different from the location of the origin  205  at CF. In the current embodiment, the projection point  510  is below the origin  205  by a distance of about 1 mm as measured in the TFP  235 . In various embodiments, the projection point  510  may be below the origin  205  be 1.5 mm. In various embodiments, the projection point  510  may be below the origin  205  by up to 3 mm. The low and more forward CG  600  results in a design that changes the playability of the golf club head  500 . As described above, a low CG (such as CG  400 ) may include a projection point at the CF or even above the CF in various designs. Because of the low and relatively forward location of the CG  600 , the projection point  510  is below CF in the current embodiment. The previously mentioned effects of CG location apply here. Several advantages are surprisingly found. First, because Δ 1  is relatively small, dynamic lofting is reduced, thereby reducing spin that may, in turn, reduce distance. Additionally, because the projection of the CG  600  is below the CF, the gear effect biases the golf ball to rotate toward the projection of the CG  600 —or, in other words, with forward spin. This is countered by the loft of the golf club head  500  imparting back spin. The overall effect is a relatively low spin profile. However, because the CG  600  is below the CF (and, thereby, below the ideal impact location) as measured along the z-axis  206 , the golf ball will tend to rise higher on impact. The result is a high launching but lower spinning golf shot on purely struck shots, which leads to better ball flight (higher and softer landing) with more distance (less energy lost to spin). 
     For the current embodiment of the golf club head  500 , CG y  is equal to Δ 1  plus the distance  241  of 13.25 mm. In the current embodiment, Δ 1  is nominally about 7 mm, so CG y  is about 20.25 mm. As previously mentioned, Δ z  is about 12.9 mm. As such, CG eff  is equal to the product of CG y  and Δ z , which, for the current embodiment, CG eff  is about 261 mm 2 . In various embodiments of the current disclosure, CG eff  may be 260-275 mm 2 . In various embodiments, CG eff  may be 255-300 mm 2 . In various embodiments, CG eff  may be 245-275 mm 2 . In various embodiments, CG eff  of the current disclosure may be at most 275 mm 2 . In various embodiments, CG eff  of the current disclosure may be at most 250 mm 2 . In various embodiments, CG eff  of the current disclosure may be at most 225 mm 2 . In various embodiments, CG eff  of the current disclosure may be at most 200 mm 2 . D CG  is determined as mentioned above with respect to golf club head  100 . D CG  for the current embodiment of about 15 degrees loft (θ) and CG y  of 20.25 is about 19.5 mm. In various embodiments, D CG  may be 15-25 mm. In various embodiments, D CG  may be 10-30 mm. In various embodiments, D CG  may be determined from other physical aspects of the golf club head  500  as described herein. 
     One of skill in the art would understand that the CG eff  measurement is particularly difficult to achieve in a fairway wood type golf club head. For example, low CG eff  numbers may be seen in hybrid type golf club heads and, particularly, in iron type golf club heads. As such, one of skill in the art would understand that various measurements as combined herein may apply to fairway wood or driver type golf club heads but may not apply to hybrid type golf club heads. 
     While these effects are seen, it has previously been impossible to implement such design elements within a golf club head that included a coefficient of restitution feature. Because the designs of features for increasing coefficient of restitution described in U.S. patent application Ser. No. 12/791,025, filed Jun. 1, 2010, and U.S. patent application Ser. No. 13/338,197, filed Dec. 27, 2011, which are incorporated by reference herein in their entirety, include physical elements making up the coefficient of restitution features of those designs, it may not be possible to locate a large amount of mass in the vicinity of the coefficient of restitution features and proximate the face of the golf club head. As such, it may not be possible to create a low and forward CG location along with a coefficient of restitution feature as described in previous designs. Such a combination is one inventive element among many of the current disclosure. 
     As can be seen with reference to  FIG. 8 , the CORF  800  is substantially the same for the current embodiment as for prior embodiments of this disclosure, in that various dimensions and surfaces are similar. However, there are some differences. Particularly, the weight pad  550  includes an overhang portion  567  that about fully covers the CORF  800  in the current embodiment. A thickness  572  of about 6.1 mm as measured in in the direction of the z-axis  206  (not shown in the current view) is seen that is notably larger than the thickness  372 . In various embodiments, the thickness  572  may be 5.5-7 mm. In various embodiments, the thickness  572  may be 4-10 mm. In various embodiments, the thickness  572  may be up to 12.5 mm. In the current embodiment, the overhang portion  567  includes a sloped end  574  that is about parallel to the face  110  (or, more appropriately, to the TFP  235 , not shown in the current view). A separation distance  576  of about 4.5 mm is seen as the distance between the inner surface  112  of the face  110  and the sloped end  574  of the overhang portion  567  as measured orthogonal to the TFP  235 . In various embodiments, the separation distance  576  may be 4-5 mm. In various embodiments, the separation distance  576  may be 3-6 mm. The overhang portion  567  includes a faceward most point  581  that is the point of the overhang portion  567  furthest toward the leading edge  170  as measured in the direction of the y-axis  207 . 
     As previously discussed, a ratio of each of the offset distance  392 , the offset to ground distance  393 , and the vertical surface height  394  to the thickness  572  (or thickness  372 ) is less than or equal to 1. In the current embodiment, the ratio of each of the offset distance  392 , the offset to ground distance  393 , and the vertical surface height  394  to the thickness  572  is less than 0.5, or, in some embodiments, less than 0.33. In various embodiments, the CORF  300  may be characterized in terms of the termination surface to ground distance  397  to achieve the CORF mass density ratio as previously discussed. For the current embodiment, the CORF mass density ratio is less than about 0.55, and may be less than 0.40 in various embodiments, less than 0.50 in various embodiments, or less than 0.60 in various embodiments depending on the thickness of the overhang portion  567  and the features of the golf club head  500  that allow the termination surface to ground distance  397  to be minimized. 
     In the current embodiment, a weight of the golf club head  500  is about 215 grams and may be anywhere from 180 grams to 260 grams in various embodiments. In the current embodiment, the weight pad  550  makes up about 43%-44%, or about 93 grams, of the weight of the golf club head  500 . In various embodiments, the weight pad  550  may be 35%-50% of the weight of the golf club head  500 . As can be understood by one of skill in the art, locating as much mass at a particular location in a golf club head can have a dramatic effect on the location of the CG of a particular golf club head. 
     As seen in  FIG. 9 , the golf club head  500  includes the weight pad  550 . The weight pad  550  includes a dimension  571  that is the largest length of the weight pad  550  as measured along the x-axis  208 . The dimension  571  is about 79.5 mm in the current embodiment. In various embodiments, the dimension  571  may be 75-85 mm. In various embodiments, the dimension  571  may be 70-90 mm. The weight pad  550  of the current embodiment extends to its edges where it contacts the skirt  140 . In the current view, the area of contact between the weight pad  550  and the skirt  140  on the heel  190  is out of view. The location of contact is as measured. Also, the weight pad  550  of the current embodiment does not terminate at the skirt  140  for all its ends. In the current embodiment, end  573  terminates into an inner surface of the sole  130 . 
     A heel stress relief pad  584  and a toe stress relief pad  586  can be seen proximate the ends  434 , 436  of the CORF  300  beneath the overhang portion  567 . The stress relief pads  584 , 586  are regions of increased thickness of material to prevent cracking of the CORF  300  in various embodiments. Because the weight pad  550  overhangs the CORF  300 , regions of the weight pad  550  in proximity to the CORF  300  need not be substantially reinforced as may have been seen in prior embodiments. A face end  592  of the weight pad  550  (including the sloped end  574 ) generally follows the curvature of the CORF  300  in the current embodiment. Indentations  594 , 596  of the face end  592  occur proximate the ends  434 , 436  of the CORF  300 . Otherwise, the face end  592  of the weight pad  550  generally follows the curvature of the face  110 . A further view of the golf club head  500  is seen in  FIG. 10 . 
     Another embodiment of a golf club head  1000  is shown in  FIG. 11 . The golf club head  1000  is substantially similar to golf club head  500  in shape and features. There are some substantial differences. However, as stated previously, for the sake of simplicity of the disclosure, where features are similarly drawn and/or identified with common reference identifiers, one of skill in the art would understand that the features of one embodiment may be included in another embodiment where the inclusion of such features would not contradict other elements of the disclosure. Even where reference identifiers are not included in the several exemplary embodiments described herein, one of skill in the art would understand that similarly drawn features are intended to be consistent amongst the several embodiments except wherein the disclosure contradicts such assumption or for which such assumption would be antithetical so some explicit disclosure. 
     In the current embodiment, the golf club head  1000  includes a CG  1400 , which is set at Δ z  and Δ 1 , which projection  1505  and projection point  1510 . In the current embodiment, CG  1400 , Δ z , Δ 1 , projection  1505 , and projection point  1510  are all about the same as CG  600 , Δ z , Δ 1 , projection  505 , and projection point  510  for golf club head  500  as previously described with reference to  FIG. 7 , although such features of the current embodiment may be nominally different. The weight pad  1350  is about the same mass as the weight pad  550 , although various features of the weight pad  550  are different, as will be described below. The golf club head  1000  includes CORF  1300 , which includes many features consistent with CORF  800  and CORF  300 . 
     As seen with reference to  FIG. 12 , the CORF  1300  of the current embodiment is shaped similarly to the CORF  800 . There are several substantial differences. First, the CORF  1300  includes a retention feature  1325 . The retention feature  1325  in the current embodiment is a channel defined in the weight pad  1350 . The retention feature  1325  is defined by The retention feature  1325  follows the general contour of the CORF  1300 . A termination surface  1390  is seen in the current view. The termination surface  1390  is disposed at an angle  1391  with respect to the direction of the y-axis  207  (not shown in  FIG. 12 ). The weight pad  1350  includes an overhang portion  1367  which has a sloped end  1374 . The sloped end  1374  is disposed at an angle  1396  with respect to an inner surface of the face  110 . A fillet  1397  is seen at a top edge of the overhang portion  1367 . A thickness  1372  of the overhang portion  1367  measured in the direction of the z-axis  206  is about 5.4 mm and is the largest thickness of the overhang portion  1367  because the angle  1391  causes the overhang portion  1367  to taper. In various embodiments, the thickness  1372  may be 5.5-7 mm. In various embodiments, the thickness  1372  may be 4-8 mm. In various embodiments, the thickness  1372  may be up to 12.5 mm. 
     As previously discussed, a ratio of the offset distance  1392  to the thickness  1372  (or thicknesses  372 , 572 ) is less than or equal to 1. In the current embodiment, the ratio of the offset distance  1392  to the thickness  1372  is less than 0.5. In various embodiments, this ratio may be less than 0.4. In various embodiments, this ratio may be less than 0.33. In various embodiments, the CORF  300  may be characterized in terms of the termination surface to ground distance  397  to achieve the CORF mass density ratio as previously discussed. In the current embodiment, the termination surface to ground distance  397  is measured from a lowest point  1347  of the termination surface. For the current embodiment, the CORF mass density ratio is less than about 0.55, and may be less than 0.40 in various embodiments, less than 0.50 in various embodiments, or less than 0.60 in various embodiments depending on the thickness of the overhang portion  567  and the features of the golf club head  500  that allow the termination surface to ground distance  397  to be minimized. 
     Unlike in prior embodiments, the overhang portion  1367  includes a substantial overhang  1382  as measured orthogonal to the TFP  235  from a faceward most point  1381  of the overhang portion  1397  to an end of the first sole portion  1355 . The faceward most point  1381  is the point of the overhang portion  1367  furthest toward the leading edge  170  as measured in the direction of the y-axis  207 . The overhang  1382  is about 0.75 mm in the current embodiment. In various embodiments, the overhang  1382  may be 0.5-1.5 mm. Because of the substantial overhang  1382 , the angle  1391  allows for flow of the relatively viscous polyurethane plugging material into the CORF  1300  upon injection. 
     As previously described (particularly with reference to CORF  300 ), the golf club heads of the current disclosure (golf club head  100 , golf club head  500 , golf club head  1000 ) include a plugging material injected into the CORF  300 ,  800 ,  1300 . The plugging material may be various materials in various embodiments depending upon the desired performance. In the current embodiment, the plugging material is polyurethane, although various relatively low modulus materials may be used, including elastomeric rubber, polymer, various rubbers, foams, and fillers. In the current embodiment, the plugging material is a polyurethane reactive adhesive. The plugging material of the current embodiment is applied at 250° F. The plugging material of the current embodiment has a viscosity of 16,000 cps, although in various embodiments the plugging material may be of a viscosity of 7,000-16,000 cps, and in various embodiments may be up to 20,000 cps. The plugging material of the current embodiment has a Shore D hardness of 47. In various embodiments, the Shore D hardness may be 45-50. In various embodiments, the Shore D hardness may be 35-55. The plugging material of the current embodiment has a modulus of 3,300 psi. In various embodiments, the modulus may be 2,850-5,600 psi. The plugging material of the current embodiment has an ultimate tensile strength of 3,200 psi. In various embodiments, the plugging material may have an ultimate tensile strength of 2,750-3,900 psi. The plugging material of the current embodiment may have an elongation at break of 600-860%. The ranges cited apply to plugging materials of the current embodiment. As stated in this disclosure, various materials may be used as plugging materials and have properties outside of those listed with respect to the current embodiment. Should design goals change, it may be appropriate to change plugging materials to achieve desired design goals. 
     The plugging material should not substantially prevent deformation of the golf club head  100 , particularly of the face  110 . In use, golf club heads of the current disclosure (golf club head  100 , golf club head  500 , golf club head  1000 ) experience peak forces of greater than 2,000 pounds. Under such environment, the face  110  of the club head deforms, as discussed previously with reference to COR. Because of the face  110  of the golf club heads of the current disclosure (golf club head  100 , golf club head  500 , golf club head  1000 ) include roll and bulge radii, deformation of the face  110  causes the edges to expand. Particularly in the region of the CORFs  300 ,  800 ,  1300 , this causes the first sole portion  355  to expand downward in the direction of the z-axis  206  (not shown in  FIG. 12 ). As such, the first sole portion  355  travels away from the termination surface  1390 . In some embodiments and combination of materials, the plugging material may become loosened upon the deformation of the face  110  and, particularly, upon the deformation of the first sole portion  355 . As such, the retention feature  1325  creates a void into which the plugging material may flow, creating a mechanical interference to prevent the plugging material from becoming removed from the CORF  1300 . In various embodiments, the retention feature  1325  may be various shapes, sizes, and/or include various features to redistribute mass, to aid in manufacturability, or to improve coupling with the plugging material. Also, an offset distance  1392  as measured in the direction of the z-axis  206  between the faceward most point  1381  and the low point  384  is greater than seen in prior embodiments, and may be about 2.3 mm in various embodiments. In various embodiments, the offset distance  1392  may be 1-3 mm. In various embodiments, the offset distance  1392  may be as little as 0.5 mm and up to about 12.5 mm. It should be noted that, because the plugging material may be viscous, in various embodiments the plugging material may not entirely fill the CORF ( 300 ,  800 ,  1300 ) and/or the retention feature  1325 . In various embodiments, the plugging material may entirely fill the CORF ( 300 , 800 , 1300 ) and/or the retention feature  1325 . However, the various features are included to at least partially retain the plugging material. 
     With reference to  FIG. 13 , the weight pad  1350  of the current embodiment includes similar general dimensions to weight pad  550 . The weight pad  1350  includes indentations  1394 , 1396  that are not as substantial as indentations  594 , 596 . Another view of the golf club head is seen in  FIG. 14 . 
     In at least one example test, the CORF  300  and other CORFs of the current disclosure were compared with golf club heads that were identical but did not have a CORF. As seen with reference to  FIG. 15 , golf club heads of the current disclosure (golf club head  100 , golf club head  500 , golf club head  1000 ) with CORFs (CORF  300 , CORF  800 , CORF  1300 ) were tested for COR against identical heads without CORFs. Impacts tested for COR were measured at locations at the CF (CF), 5 mm above the CF (5 High) in the TFP  235 , 5 mm below the CF (5 Low) in the TFP  235 , 7.5 mm toward the heel from the CF (7.5 Heel) in the TFP  235  and along the x-axis  208 , and 7.5 mm toward the toe from the CF (7.5 Toe) in the TFP  235  and along the x-axis  208 . COR data gathered showed the changes in COR for each location from standard as measured below. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Test 1 
                   
                   
                   
               
               
                   
                 Position 
                 No CORF 
                 CORF 
                 Change 
               
               
                   
                   
               
               
                   
                 CF 
                 0.794 
                 0.811 
                 0.017 
               
               
                   
                 5 High 
                 0.782 
                 0.798 
                 0.016 
               
               
                   
                 5 Low 
                 0.761 
                 0.79 
                 0.029 
               
               
                   
                 7.5 Heel 
                 0.772 
                 0.794 
                 0.022 
               
               
                   
                 7.5 Toe 
                 0.777 
                 0.785 
                 0.008 
               
               
                   
                 Average 
                 0.777 
                 0.796 
                 0.018 
               
               
                   
                   
               
               
                   
                 Test 2 
                   
               
               
                   
                 Position 
                 No Slot 
                 MR Slot 
                 Change 
               
               
                   
                   
               
               
                   
                 CF 
                 0.79 
                 0.806 
                 0.016 
               
               
                   
                 5 High 
                 0.785 
                 0.798 
                 0.013 
               
               
                   
                 5 Low 
                 0.764 
                 0.779 
                 0.015 
               
               
                   
                 7.5 Heel 
                 0.766 
                 0.789 
                 0.023 
               
               
                   
                 7.5 Toe 
                 0.773 
                 0.789 
                 0.016 
               
               
                   
                 Average 
                 0.776 
                 0.792 
                 0.017 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen, the inclusion of CORFs of the current disclosure (CORF  300 , CORF  800 , CORF  1300 ) provided increased COR at all locations of the face and more consistent COR from strikes in the CF to off-center strikes. 
     As seen in  FIGS. 16A and 16B , plugging material  801 , 1301  is found in CORFs  800 , 1300 , respectively. The plugging material  801 , 1301  may be molded in place, injected into the CORFs  800 , 1300 , or otherwise placed in the CORFs  800 , 1300 , among other possible assembly and manufacturing methods. As seen with reference to  FIG. 16A , the plugging material  801  is placed in the CORF  800  such that an outer surface  804  is about flush with a surface of the sole  130 , with a first end  806  about flush with the first sole portion  355  and a second end  808  about flush with the first weight pad portion  365  and almost in contact with the GP. The first end  806  is disposed at a distance  809  above the ground of about 0.72 mm that is about consistent with an outer surface of the first sole portion  355 . The distance  809  may be 0.5-1.0 mm in various embodiments. The distance  809  may be 0-1.5 mm in various embodiments. The distance  809  may be up to 2 mm in various embodiments. An inner surface  811  of the plugging material  801  extends beyond the faceward most point  581 , which helps provide surface are and mechanical retention properties. In various embodiments, the plugging material  801  may not extend beyond the faceward most point  581  or may have another advantage associated with another configuration. As can be seen, the plugging material  801  of the current embodiment does not fully engage the transition of the vertical surface  385  to the termination surface  390 , but instead there may be an air bubble between the plugging material  801  and the joint of the vertical surface  385  and the termination surface  390 . In various embodiments, the plugging material fully engages the entirety of the CORF. 
     As seen with reference to  FIG. 16B , the plugging material  1301  is placed in the CORF  1300  such that an outer surface  1304  is disposed inward from the surface of the sole  130 . As contrasted with outer surface  804 , outer surface  1304  includes a first end  1306  and a second end  1308  that are about flush with ends of the bevel  375 . The first end  1306  is disposed at a distance  1309  above the GP that is about 1.30 mm. In various embodiments, the distance  1309  may be 1-2 mm. In various embodiments, the distance  1309  may be 0.5-1.5 mm. In various embodiments, the distance  1309  may be up to 4 mm. The second end  1308  is disposed at a distance  1307  above the GP that is about 0.92 mm. In various embodiments, the distance  1307  may be 0.75-1.5 mm. In various embodiments, the distance  1307  may be 0.5-2 mm. In various embodiments, the distance  1307  may be up to 3 mm. An inner surface  1311  of the plugging material  1301  extends beyond the faceward most point  1381 , which helps provide surface are and mechanical retention properties. In various embodiments, the plugging material  1301  may not extend beyond the faceward most point  1381  or may have another advantage associated with another configuration. 
     As can be seen, the plugging material  1301  of the current embodiment has extended into the retention feature  1325 . However, the plugging material  1301  of the current embodiment does not fully engage the retention feature  1325 . Instead there may be various air bubbles between the plugging material  1301  and the CORF  1300 . However, sufficient volume of plugging material  1301  has engaged the retention feature  1325  to provide benefits of retaining the plugging material  1301  inside the CORF  1300  even under extreme deformation of the face  110  and the golf club head  1000 . In various embodiments, the plugging material fully engages the entirety of the CORF. One of skill in the art would understand that features and explanations related to  FIGS. 16A and 16B  may be interchanged between the two embodiments, and no one element should be considered to be binding on any embodiments of the current disclosure simply because of its depiction in one figure. 
     Another embodiment of a golf club head  1500  is seen in  FIGS. 17A-17D  and includes a number of features consistent with prior embodiments of golf club heads ( 100 ,  500 ,  1000 ) of the current disclosure. The golf club head  1500  includes a CORF  1800  that is a constant radius. In the current embodiment, the constant radius of the CORF  1800  is about 44 mm. In various embodiments, the constant radius may be 38-50 mm. In various embodiments, the constant radius may be 30-60 mm. In various embodiments, the constant radius may be less than 80 mm. 
     A crown height  1862  is shown and measured as the height from the GP to the highest point of the crown  120  as measured parallel to the z-axis  206 . In the current embodiment, the crown height  1862  is about 41 mm. In various embodiments, the crown height  1862  may be 38-43 mm. In various embodiments, the crown height may be 30-50 mm. The golf club head  1500  also has an effective face height  1863  that is a height of the face  110  as measured parallel to the z-axis  206 . In the current embodiment, the face height  1863  is about 39 mm. The face height  1863  may be 2-5 mm less than the crown height in various embodiments. The face height  1863  may be 1-10 mm less than the crown height in various embodiments. The face height  1863  measures from a highest point on the face  110  to a lowest point on the face  110  proximate the leading edge  170 . A transition exists between the crown  120  and the face  110  such that the highest point on the face  110  may be slightly variant from one embodiment to another. In the current embodiment, the highest point on the face  110  and the lowest point on the face  110  are points at which the curvature of the face  110  deviates substantially from a roll radius. In some embodiments, the deviation characterizing such point may be a 10% change in the radius of curvature. Finally, an effective face position height  1864  is a height from the GP to the lowest point on the face  110  as measured in the direction of the z-axis  206 . In the current embodiment, the effective face position height  1864  is 1 mm. In various embodiments, the effective face position height  1864  may be 0-4 mm. 
     As seen with reference to  FIG. 18 , the golf club head  1500  includes a weight pad  1850 . The weight pad  1850  distributes weight similarly to prior embodiments. However, the weight pad  1850  does not have an overhang portion. Although a length  1890  of the weight pad  1850  is about the same as the length  590 , the weight pad  1850  does not include an overhang portion, so the center of the weight pad  1850  is located further rearward in the golf club head  1500 . As such, a location of a CG  1900  is further back and higher than in similar prior embodiments. Δ 1  and Δ z  are larger for the golf club head  1500  than for golf club head  500  and  1000 . A projection point of the CG  1900  onto the TFP  235  is about at the origin  205  (at CF). A thickness of the CORF  1800  is about the same as for CORF  800  and CORF  1300 . It should be noted that the origin  205  (at CF) of the current embodiment is farther from the GP than the origin  205  of prior embodiments because the crown height  1862  is larger than the crown height  162 . 
     As seen with reference to  FIG. 19 , the CORF  1800  includes several features not seen in prior embodiments. A first sole portion  2355  extends toward and defines the CORF  1800 . The CORF  1800  is defined on its other end by a first weight pad portion  2365 . As can be seen, a radiused edge  2375  (shown as  2375   a,b ) of the CORF  1800  is included in the current embodiment. The first sole portion  2355  includes an inner ledge portion  2380  that is a thickened region or boss of the first sole portion  2355 . 
     The weight pad  1850  is disposed further rearward in the golf club head  1500  of the current embodiment, as seen with reference to  FIG. 20 . A length  2290  of the weight pad  1850  is about 20 mm in the current embodiment and is a little bit less than the length  590 . In various embodiments, the length  2290  may be 18-24 mm. In various embodiments, the length  2290  may be 12-30 mm. However, the weight pad  1850  of the current embodiment includes a heel extension  2234  and a toe extension  2236 . A distance  2310  of the weight pad  1850  as measured to the heel extensions  2234  and the toe extension  2236  is about 22.5 mm in the current embodiment. In various embodiments, the distance  2310  may be 20-25 mm. In various embodiments, the distance may be 15-30 mm. The weight pad  1850  defines a CORF contour  2247 . The CORF contour  2247  provides a void that about follows the curvature of the CORF  1800 . A dimension  2271  of the weight pad  1850  is about 75 mm in the current embodiment, or a little less than the dimension  571 . In various embodiments, the dimension  2271  may be 70-80 mm. In various embodiments, the dimension  2271  may be 60-85 mm. 
     General dimensions of the CORF  1800  are seen with reference to  FIG. 21 . A distance  2452  is shown between a toeward end  2436  and the heelward end  2434  as measured in the direction of the x-axis  208 . In the current embodiment, the distance  2452  is 48-50 mm. In various embodiments, the distance  2452  may be 45-55 mm. In various embodiments, the distance  2452  may be 40-60 mm. In various embodiments, the distance  2452  may be larger or smaller than the range shown for the current embodiment. The CORF  1800  includes a distance  2454  as measured in the direction of the y-axis  207 . In the current embodiment, the distance  2454  is 9-10 mm. In various embodiments, the distance  2454  may be 8-11 mm. In various embodiments, the distance  2454  may be 7-14 mm. In various embodiments, the distance may be larger or smaller than the range shown for the current embodiment. 
     In at least one example test, the CORF  1800  of the current disclosure was compared with golf club heads that were identical but did not have a CORF. Positions of the current test are as seen with reference to  FIG. 15 . Impacts tested for COR were measured at locations at the CF (CF), 5 mm above the CF (5 High) in the TFP  235 , 5 mm below the CF (5 Low) in the TFP  235 , 7.5 mm toward the heel from the CF (7.5 Heel) in the TFP  235  and along the x-axis  208 , and 7.5 mm toward the toe from the CF (7.5 Toe) in the TFP  235  and along the x-axis  208 . COR data gathered showed the changes in COR for each location from standard as measured below. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Position 
                 No Slot 
                 CORF 1800 
                 Change 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Test 1 
                   
                   
                   
               
               
                   
                 CF 
                 0.799 
                 0.814 
                 0.015 
               
               
                   
                 5 High 
                 0.794 
                 0.788 
                 −0.006 
               
               
                   
                 5 Low 
                 0.771 
                 0.784 
                 0.013 
               
               
                   
                 7.5 Heel 
                 0.793 
                 0.797 
                 0.004 
               
               
                   
                 7.5 Toe 
                 0.765 
                 0.781 
                 0.016 
               
               
                   
                 Average 
                 0.784 
                 0.793 
                 0.008 
               
               
                   
                 Test 2 
               
               
                   
                 CF 
                 0.791 
                 0.810 
                 0.019 
               
               
                   
                 5 High 
                 0.786 
                 0.800 
                 0.014 
               
               
                   
                 5 Low 
                 0.760 
                 0.778 
                 0.018 
               
               
                   
                 7.5 Heel 
                 0.782 
                 0.795 
                 0.013 
               
               
                   
                 7.5 Toe 
                 0.756 
                 0.786 
                 0.030 
               
               
                   
                 Average 
                 0.775 
                 0.794 
                 0.019 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen, the inclusion of CORF  1800  provided increased COR at all locations of the face other than one location in one test. COR was also more consistent across the face. 
     An additional COR measurement was taken at the balance point of the golf club head  1500 . The average numbers in the above chart did not take into account the measurements at the balance point, shown below. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Position 
                 No Slot 
                 CORF 1800 
                 Change 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Test 1 
                   
                   
                   
               
               
                   
                 BP 
                 0.800 
                 0.814 
                 0.014 
               
               
                   
                 Test 2 
               
               
                   
                 BP 
                 0.795 
                 0.810 
                 0.015 
               
               
                   
                   
               
            
           
         
       
     
     As seen with reference to the charts above, the CORF  1800  increased COR at virtually all positions on the face in each test. 
     Another embodiment of a golf club head  2000  is seen with reference to  FIG. 22 . The golf club head  2000  includes many features similar to other golf club heads ( 100 ,  500 ,  1000 ,  1500 ) of the current disclosure. The golf club head  2000 , however, includes a sole wrap insert  2700  that includes the various features of the CORF  2300 . In shape, the CORF  2300  is similar to the CORFs  300 , 800 . However, CORF  2300  is included on a sole wrap insert  2700 . 
     In many golf club heads, the face (such as face  110 ) is a part manufactured separately from the golf club body. The face is typically welded to the golf club body or otherwise joined in method suitable for striking a golf ball. In some golf club heads, the face may be of a different material than the golf club body. For example, to reduce costs, the golf club body may be made of a low quality steel while the face is made a high quality steel that can withstand impacts, even with thinner faces. In the embodiments of the current disclosure—and in embodiments that seek to implement CORFs such as those disclosed herein without such weight redistribution features described herein—it may be advantageous to construct a golf club head (such as golf club head  2000 ) with an insert that is welded to the golf club body that is not just a face insert but includes the CORF in a piece that wraps to the sole of the golf club head. One challenge in design of CORF is stress concentrations in various features of the CORFs. As previously mentioned, certain features as described in the current disclosure address stress concentrations in the CORF and in surrounding features to reduce and to eliminate potential for failure of the golf club head. In embodiments including the sole wrap insert  2700 , the entirety of the face  110  through the sole  130  are of high-strength material typically used only for face inserts. For example, in one embodiment, a high nickel content steel alloy having a yield strength of 2,000 MPa with 11% elongation may be used to fabricate the sole wrap insert  2700 , allowing for thinner construction with greater strength of material. The steel alloy includes a composition of about 18-19% nickel, about 8-9.5% cobalt, about 4.5-5.1% molybdenum, about 0.5-1.0% titanium, 0.05-0.15% aluminum, less than 0.10% of each of carbon, phosphorus, silicon, calcium, zirconium, manganese, sulfur, and boron, with the balance of the composition being of iron. The steel alloy used to fabricate the sole wrap insert  2700  can be a maraging steel having a high nickel content between 16%-20%. In other embodiments, a steel alloy having a nickel content of 14%-17% can be used. The steel alloy may be heat treated to achieve higher yield strength. The sole wrap insert  2700  is joined to 17-4 stainless steel—or various other types of material such as Custom 630 Steel by Carpenter®, Custom 455 by Carpenter®, and Custom 475 by Carpenter®—for the remainder of the golf club body. When comparing the body steel to the high strength sole wrap insert  2700  steel, the maximum ultimate tensile strength of the sole wrap insert  2700  steel at room temperature is greater than the maximum ultimate tensile strength of the body steel by about 20%-50% for any given heat treat. For example, the maximum ultimate tensile strength of the Custom 630 at room temperature is about 1365 MPa for any given heat treatment compared to 2000 MPa for the high nickel content steel described above. Thus, a 46% increase in maximum ultimate tensile strength at room temperature is achieved by the high nickel content steel. Similar benefits are seen when using a high strength or high performance titanium alloy sole wrap insert  2700  with a more traditional (and perhaps lower cost) titanium alloy golf club body. In various embodiments of the current disclosure, various materials described herein may be imported to the face  110  or the golf club body of the prior embodiments without the use of a sole wrap insert  2700 . 
     The use of a high strength material in conjunction with a more traditional golf club head material has multiple advantages. The high strength material may be made thinner and may be capable of experiencing greater deflection on impact, especially if such material is not coupled to the golf club body in close proximity to the striking area. This allows for higher COR and use of less material than would be possible for a smaller face insert or a lower quality material. Second, the coupling to a lower cost material golf club body reduces overall cost while maintaining exceptional performance characteristics. In various embodiments, a sole wrap insert without a CORF may be used and may see some of the benefit associated with the current application. 
     Another embodiment of a golf club head  2500  is shown in  FIG. 23 . The golf club head  2000  includes similar features to prior embodiments of golf club heads ( 100 ,  500 ,  1000 ,  1500 ,  2000 ) of the current disclosure. For the sake of simplicity of the disclosure, where features are similarly drawn and/or identified with common reference identifiers, one of skill in the art would understand that the features of one embodiment may be included in another embodiment where the inclusion of such features would not contradict other elements of the disclosure. Even where reference identifiers are not included in the several exemplary embodiments described herein, one of skill in the art would understand that similarly drawn features are intended to be consistent amongst the several embodiments except wherein the disclosure contradicts such assumption or for which such assumption would be antithetical so some explicit disclosure. 
     The golf club head  2500  includes CORF  2800 . CORF  2800  is similar to prior embodiments of CORFs of the current disclosure (CORF  300 ,  800 ,  1300 ,  1800 ,  2300 ). The golf club head  2500  includes weight pad  2550  that is similar to prior embodiments of weight pads ( 350 ,  550 ,  1350 , 1850 ) of the current disclosure. 
     As seen with reference to  FIG. 24 , the CORF  2800  of the current disclosure includes radiused edges  2875  (shown as  2875   a,b ) in the current embodiment where a bevel  375  may previously have been seen. The weight pad  2550  includes an overhang portion  2867 . The overhang portion  2867  includes a chamfered edge  2892 . The chamfered edge  2892  may promote flow of plugging material (such as plugging material  801 , 1301 ) into the CORF  2800  and may provide additional clearance for added features of the CORF  2800 . 
     In particularly, a first sole portion  2855  includes a stress pad  2901  that is a thickened region or boss extended from the first sole portion  2855  in the direction of the z-axis  206 . In use, the CORFs of the current disclosure ( 300 ,  800 ,  1300 ,  1800 ,  2300 ,  2800 ) experience normal, shear, and multiple torsional when golf club heads of the current disclosure ( 100 ,  500 ,  1000 ,  1500 ,  2000 ,  2500 ) impact a golf ball. One of skill in the art would understand that the Von Mises stresses in the region of the CORF ( 300 ,  800 ,  1300 ,  1800 ,  2300 ,  2800 ) can exceed the ultimate stress of the material due to stress concentrations in the geometry of the CORF ( 300 ,  800 ,  1300 ,  1800 ,  2300 ,  2800 ). As such, stress concentrations in the CORF ( 300 ,  800 ,  1300 ,  1800 ,  2300 ,  2800 ) may cause failure of the golf club head due to the extremely high Von Mises stresses. To combat such stress concentrations, the embodiment of golf club head  2500  provides some benefit. 
     In various embodiments, thickening the first sole portion  355  increases the area over which force is applied, thereby reducing stress in the aggregate and reducing the chance of failure of the CORF ( 300 , 800 , 1300 , 1800 , 2300 , 2800 ). However, it was surprisingly determined that simply thickening the entirety of the first sole portion  355  may reduce COR of the golf club head. As such, the first sole portion  355  was modified to create the first sole portion  2855 . The stress pad  2901  provides added thickness of material in the region of the CORF  2800 , but the region of the first sole portion  2855  in close proximity to the face  110  remains thinner than the stress pad  2901 . It was surprisingly determined that the introduction of the stress pad  2901  reduced stress concentrations without negative effect on COR. In various embodiments, the introduction of the stress pad  2901  doubles the thickness of the first sole portion  2855  in the region of the stress pad  2901 . As can be seen, the stress pad  2901  defines a groove  2903  between the face  110  and the stress pad  2901  for at least a portion of the face  110 , as will be seen with reference to further figures. In various embodiments, the stress pad  2901  may be straight such that the groove  2903  has straight ends. In the current embodiment, the stress pad  2901  is defined by a curve  2907 . The curve  2907  is about the shape of one half of a sine wave. In various embodiments, various shapes of curves  2907  may be used, including round, squared, radiused, chamfered, and various mathematical functions. 
     Various embodiments of the stress pad  2901  are shown in  FIGS. 25A and 25B . As seen with reference to  FIG. 25A , a stress pad  2901   a  may be of about constant thickness as measured in the direction of the z-axis  206  and follow the contour of the face  110  in the direction of the x-axis  208 . The shape of the stress pad  2901   a  may be about constant in the direction of the y-axis  207  as well over its length. A second embodiment of a stress pad  2901   b  is seen with reference to  FIG. 25B . Rather than a shape that follows the contour of the face  110 , the stress pad  2901   b  tapers. The stress pad  2901   b  decreases in thickness (as measured in the direction of the z-axis  206 ) as it departs from the face  110 . As such, the stress pad  2901   b  is substantially thinner near its ends than proximate CF. 
     Stress pads  2901   a,b  are also seen with reference to  FIGS. 26A and 26B . The stress pad  2901   a  of the current embodiment has a lateral extent  2915   a  that is less than the width of the CORF  2800 . In the current embodiment, the lateral extent  2915   a  is less than the width of the central portion  422 . In various embodiments, the lateral extent  2915   a  may be larger, smaller, or equal to the width of the central portion  422  or the distance  452 . The stress pad  2901   a  also includes a full thickness extent  2917   a  for which the cross-section of the stress pad  2901   a  does not change. As can be seen, the stress pad  2901   b  has a lateral extent  2915   b  that is substantially less than a width of the central portion  422 . Additionally, the full thickness extent  2917   b  is substantially smaller than the full thickness extent  2917   a . The cross-sectional shape of the stress pad  2901   b  changes over its lateral extent  2915   b  such that few cross-sections of the stress pad  2901   b  include the same cross-sectional shape. As can be seen, an outermost edge of the stress pad  2901   b  is defined at a radius  2919 . As previously mentioned, the stress pad  2901   b  tapers. The taper of the stress pad  2901   b  is at the radius  2919 , which is of about 20-22 mm. In various embodiments, the radius  2919  may be 18-24 mm. In various embodiments, the radius  2919  may be up to 40 mm. 
     A golf club head  3000  is shown with reference to  FIG. 27 . The golf club head  3000  is part of a golf club assembly  3500  that includes flight control technology.  FIG. 27  illustrates a removable shaft system having a ferrule  3202  having a sleeve bore  3245  (shown in  FIG. 28D ) within a sleeve  3204 . A shaft (not shown) is inserted into the sleeve bore and is mechanically secured or bonded to the sleeve  3204  for assembly into a golf club. The sleeve  3204  further includes an anti-rotation portion  3244  at a distal tip of the sleeve  3204  and a threaded bore  3206  for engagement with a screw  3210  that is inserted into a sole opening  3212  defined in the club head  3000 . In one embodiment, the sole opening  3212  is directly adjacent to a sole non-undercut portion. The anti-rotation portion  3244  of the sleeve  3204  engages with an anti-rotation collar  3208  which is bonded or welded within a hosel  3150  of the golf club head  3000 . The adjustable loft, lie, and face angle system is described in U.S. patent application Ser. No. 12/687,003 (now U.S. Pat. No. 8,303,431), which is incorporated herein by reference in its entirety. The golf club assembly  3500  includes a weight  3240  for the weight port  240 . Although not shown, the shaft and a grip may be included as part of the golf club assembly  3500 . 
     The embodiment shown in  FIG. 27  includes an adjustable loft, lie, or face angle system that is capable of adjusting the loft, lie, or face angle either in combination with one another or independently from one another. An adjustable sole piece may be used in combination with the adjustable loft, lie and face angle system as described in detail in U.S. patent application Ser. No. 13/686,677 all of which is incorporated by reference herein it its entirety. For example, a first portion  3243  of the sleeve  3204 , the sleeve bore  3242 , and the shaft collectively define a longitudinal axis  3246  of the assembly. The sleeve  3204  is effective to support the shaft along the longitudinal axis  3246 , which is offset from a longitudinal axis  3248  of the by offset angle  3250 . The longitudinal axis  3248  is intended to align with the SA (seen in  FIG. 28B ). The sleeve  3204  can provide a single offset angle  3250  that can be between 0 degrees and 4 degrees, in 0.25 degree increments. For example, the offset angle can be 1.0 degree, 1.25 degrees, 1.5 degrees, 1.75 degrees, 2.0 degrees or 2.25 degrees. The sleeve  3204  can be rotated to provide various adjustments to the golf club assembly  3500  as described in U.S. patent application Ser. No. 12/687,003 (now U.S. Pat. No. 8,303,431). One of skill in the art would understand that the system described with respect to the current golf club assembly  3500  can be implemented with various embodiments of the golf club heads of the current disclosure. 
     As seen with reference to  FIGS. 28A-28D , the golf club head  3000  includes CORF  3300 . In various embodiments, the golf club head  3000  is a driver type golf club head. As compared to prior embodiments of the current disclosure, the golf club head  3000  has a crown height  3162  that is larger than prior embodiments. In the current embodiment, the crown height  3162  is about 62 mm. In various embodiments, the crown height  3162  may be 55-70 mm. In various embodiments, the crown height  3162  may be 45-75 mm. The face  110  includes an effective face height  3163  of about 52 mm. In various embodiments, the effective face height  3162  may be 47-57 mm. In various embodiments, the effective face height  3162  may be 45-60 mm. An effective face position height  3164  of the golf club head  3000  is about 4.5 mm. In various embodiments, the effective face position height  3164  may be 3-7 mm. In various embodiments, the effective face position height  3164  may be up to 12.5 mm. 
     As seen with reference to  FIGS. 29 and 30 , the golf club head  3000  of the current embodiment does not include a weight pad proximate the sole. Because the golf club head  3000  of the current embodiment is a driver type golf club head, weight is sought to be reduced to a minimum amount, and volume is sought to be maximized. As such, the golf club head  3000  of the current embodiment includes the CORF  3300  without weight relocation. In various embodiments, the golf club head  3000  may include various weight relocation mechanisms. The CORF  3300  includes an overhang portion  3367  that includes a chamfer  3371 . The CORF  3300  does not include a bevel, a radius, or a chamfer. The size of various features proximate the CORF  3300  is reduced as compared to prior embodiments. One of skill in the art would understand that various portions of the disclosure may be interchanged, and CORF  3300  may be included with prior embodiments in various embodiments of the disclosure. Additionally, various features of various embodiments of the disclosure may be used with golf club head  3000 . No one feature should be considered limiting on any particular embodiment, and one of skill in the art would understand that the various features, advantages, and elements of the various embodiments can be relocated, reconfigured, or combined as necessary to achieve the various design goals cited herein. 
     One should note that conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more particular embodiments or that one or more particular embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. 
     It should be emphasized that the above-described embodiments are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the present disclosure. Any process descriptions or blocks in flow diagrams should be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included in which functions may not be included or executed at all, may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the present disclosure. Further, the scope of the present disclosure is intended to cover any and all combinations and sub-combinations of all elements, features, and aspects discussed above. All such modifications and variations are intended to be included herein within the scope of the present disclosure, and all possible claims to individual aspects or combinations of elements or steps are intended to be supported by the present disclosure.