Patent Publication Number: US-11648445-B2

Title: Golf club head with open back cavity

Description:
CROSS REFERENCE 
     This is a continuation of U.S. patent application Ser. No. 16/784,177, filed on Feb. 6, 2020, which claims priority to U.S. Provisional Patent Appl. No. 62/802,125, filed Feb. 6, 2019. 
     U.S. patent application Ser. No. 16/784,177 is further a continuation in part of U.S. patent application Ser. No. 16/231,053, filed on Dec. 21, 2018, which is a continuation in part of U.S. patent application Ser. No. 15/628,639, filed Jun. 20, 2017, and is issued as U.S. Pat. No. 10,888,743 on Jan. 12, 2021, which is a continuation in part of U.S. patent application Ser. No. 14/920,484, filed Oct. 22, 2015, and which is a continuation in part of U.S. patent application Ser. No. 14/920,480, filed Oct. 22, 2015, and is issued as U.S. Pat. No. 10,688,350 on Jun. 23, 2020. 
     U.S. patent application Ser. No. 16/231,053, filed on Dec. 21, 2018, is also a continuation in part of U.S. patent application Ser. No. 15/435,054, filed on Feb. 16, 2017, and is issued as U.S. Pat. No. 11,027,177 on Jun. 8, 2021, which is a continuation in part of Ser. No. 14/920,484, filed on Oct. 22, 2015. Further, U.S. patent application Ser. No. 14/920,484, filed on Oct. 22, 2015, claims priority to U.S. Provisional Patent Appl. 62/206,152, filed Aug. 17, 2015, U.S. Provisional Patent Appl. No. 62/131,739, filed Mar. 11, 2015, U.S. Provisional Patent Appl. No. 62/105,460, filed on Jan. 20, 2015, U.S. Provisional Patent Appl. No. 62/105,464, filed on Jan. 20, 2015, and U.S. Provisional Patent Appl. No. 62/068,232, filed on Oct. 24, 2014. 
     U.S. patent application Ser. No. 14/920,480, filed on Oct. 22, 2015, also claims priority to U.S. Provisional Patent Appl. 62/206,152, filed Aug. 17, 2015, U.S. Provisional Patent Appl. No. 62/131,739, filed Mar. 11, 2015, U.S. Provisional Patent Appl. No. 62/105,460, filed on Jan. 20, 2015, U.S. Provisional Patent Appl. No. 62/105,464, filed on Jan. 20, 2015, and U.S. Provisional Patent Appl. No. 62/068,232, filed on Oct. 24, 2014. 
     U.S. patent application Ser. No. 15/435,054, filed on Feb. 16, 2017, also claims priority to U.S. Provisional Patent Appl. No. 62/313,215, filed on Mar. 25, 2016, and U.S. Provisional Patent Appl. No. 62/295,565, filed on Feb. 16, 2016. 
     U.S. patent application Ser. No. 16/231,053, filed on Dec. 21, 2018, claims priority to U.S. Provisional Patent Appl. No. 62/610,053, filed on Dec. 22, 2017, and is also a continuation-in-part of U.S. patent application Ser. No. 15/908,427, filed Feb. 28, 2018, which is a continuation-in-part of U.S. patent application Ser. No. 14/920,484, filed Oct. 22, 2015. Furthermore, U.S. patent application Ser. No. 15/628,639, filed on Jun. 20, 2017, and further claims priority to U.S. Provisional Patent Appl. No. 62/484,529 filed on Apr. 12, 2017, U.S. Provisional Patent Appl. No. 62/462,250, filed on Feb. 22, 2017, U.S. Provisional Patent Appl. No. 62/436,019, filed on Dec. 19, 2016, and U.S. Provisional Patent Appl. No. 62/352,495, filed on Jun. 20, 2016. 
     The contents of all of the above-described disclosures are incorporated fully herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to golf clubs and relates more particularly to golf club heads with energy storage characteristics. 
     BACKGROUND 
     Golf club manufacturers have designed golf club heads to relieve stress in the strikeface of the golf club head. In many instances, these designs do not allow the golf club head to flex in the crown to sole direction. Additionally, these designs may not change where peak bending of the golf club head occurs and do not allow additional storage of spring energy in the golf club head due to impact with the golf ball. Additional spring energy can increase ball speed across the strikeface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To facilitate further description of the embodiments, the following drawings are provided in which: 
         FIG.  1    depicts a back, toe-side perspective view of a golf club head according to an embodiment; 
         FIG.  2    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  1   ; 
         FIG.  3    depicts a cross-sectional view of the golf club head of  FIG.  1    along the cross-sectional line XII-XII of  FIG.  1   ; 
         FIG.  4    depicts a view of a portion of the golf club head of  FIG.  3    and a view of the same area of a standard golf club head; 
         FIG.  5    depicts a back, toe-side perspective view of a golf club according to another embodiment; 
         FIG.  6    depicts a cross-sectional view of the golf club head of  FIG.  5    along the cross-sectional line XVI-XVI of  FIG.  5   ; 
         FIG.  7    depicts a flow diagram illustrating a method of manufacturing a golf club head according to an embodiment of another method; 
         FIG.  8    depicts a back perspective view of a golf club head according to yet another embodiment; 
         FIG.  9    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  8   ; 
         FIG.  10    depicts a cross-sectional view of the golf club head of  FIG.  8    along the cross-sectional line XXIV-XXIV of  FIG.  8   ; 
         FIG.  11    depicts a view of a portion of the golf club head of  FIG.  10    and a view of the same area of a standard golf club head; 
         FIG.  12    depicts a simplified cross sectional view of the golf club head of  FIG.  8   , similar to the detailed cross-sectional view of the golf club head in  FIG.  10   ; 
         FIG.  13    depicts a back perspective view of a golf club head according to still yet another embodiment; 
         FIG.  14    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  13   ; 
         FIG.  15    depicts a cross-sectional view of the golf club head of  FIG.  13    along the cross-sectional line XXIX-XXIX of  FIG.  13   ; 
         FIG.  16    depicts a view of a portion of the golf club head of  FIG.  15    and a view of the same area of a standard golf club head; 
         FIG.  17    depicts a simplified cross-sectional view of the golf club head of  FIG.  13   , similar to the detailed cross-sectional view of the golf club head in  FIG.  15   ; 
         FIG.  18    depicts a back perspective view of a golf club head according to still yet another embodiment; 
         FIG.  19    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  18   ; 
         FIG.  20    depicts a cross-sectional view of the golf club head of  FIG.  18    along the cross-sectional line IV-IV of  FIG.  18   ; 
         FIG.  21    depicts a portion of the golf club head of  FIG.  20   ; 
         FIG.  22    depicts a simplified cross-sectional view of the golf club head of  FIG.  18   , similar to the detailed cross-sectional view of the golf club head in  FIG.  20   ; 
         FIG.  23    depicts a back perspective view of a golf club head according to still yet another embodiment; 
         FIG.  24    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  23   ; 
         FIG.  25    depicts a cross-sectional view of the golf club head of  FIG.  23    along the cross-sectional line IX-IX of  FIG.  23   ; 
         FIG.  26    depicts a portion of the golf club head of  FIG.  25   ; 
         FIG.  27    depicts a simplified cross-sectional view of the golf club head of  FIG.  23   , similar to the detailed cross-sectional view of the golf club head in  FIG.  25   ; 
         FIG.  28    depicts an interior view of a portion of the golf club head of  FIG.  23   ; 
         FIG.  29    depicts a front perspective view of the golf club head of  FIG.  23   ; 
         FIG.  30    depicts a back perspective view of a golf club head according to still yet another embodiment; 
         FIG.  31    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  30   ; 
         FIG.  32    depicts a cross-sectional view of the golf club head of  FIG.  30    along the cross-sectional line XLVI-XLVI of  FIG.  30   ; 
         FIG.  33    depicts a portion of the golf club head of  FIG.  32   ; 
         FIG.  34    depicts a simplified cross-sectional view of the golf club head of  FIG.  30   , similar to the detailed cross-sectional view of the golf club head in  FIG.  33   . 
         FIG.  35    depicts a back perspective view of a golf club head according to still yet another embodiment; 
         FIG.  36    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  35   ; 
         FIG.  37    depicts a cross-sectional view of the golf club head of  FIG.  35    along the cross-sectional line LI-LI of  FIG.  35   ; 
         FIG.  38    depicts a portion of the golf club head of  FIG.  35   ; 
         FIG.  39    depicts a simplified cross-sectional view of the golf club head of  FIG.  35   , similar to the detailed cross-sectional view of the golf club head in  FIG.  37   . 
         FIG.  40    depicts an interior view of a portion of the golf club head of  FIG.  35   ; 
         FIG.  41    depicts a front perspective view of the golf club head of  FIG.  35   ; 
         FIG.  42    depicts a back perspective view of a golf club head according to still yet another embodiment; 
         FIG.  43    depicts a back, heel-side perspective view of the golf club head according to the embodiment of  FIG.  42   ; 
         FIG.  44    depicts a cross-sectional view of the golf club head of  FIG.  42    along the cross-sectional line LVIII-LVIII of  FIG.  42   ; 
         FIG.  45    depicts a portion of the golf club head of  FIG.  44   ; 
         FIG.  46    depicts a simplified cross-sectional view of the golf club head of  FIG.  42   , similar to the detailed cross-sectional view of the golf club head in  FIG.  45   ; 
         FIG.  47    depicts a cross-sectional view of the heel portion of the golf club head of  FIG.  42   , along the cross-sectional line LXI-LXI; and 
         FIG.  48    depicts an front view of the golf club head of  FIG.  42   , along the cross-sectional line LXII-LXII. 
         FIG.  49    is a back perspective view of a golf club head. 
         FIG.  50    is a back, heel-side perspective view of the golf club head of  FIG.  49   . 
         FIG.  51    is a front, toe-side perspective view of the golf club head of  FIG.  49   . 
         FIG.  52    is a front, toe-side exploded perspective view of the golf club head of  FIG.  49   . 
         FIG.  53    is a front, heel-side perspective view of the golf club head of  FIG.  49    with portions removed. 
         FIG.  54    is a back perspective view of the golf club head of  FIG.  49    with portions removed. 
         FIG.  55    is a cross-sectional view of the golf club head of  FIG.  49    taken along line  7 - 7  of  FIG.  49   . 
         FIG.  56    is another cross-sectional view of the golf club head of  FIG.  49    taken along line  8 - 8  of  FIG.  49   . 
         FIG.  57    is another cross-sectional view of a portion of the golf club head of  FIG.  49    taken along line  7 - 7  of  FIG.  49   . 
         FIG.  58    is another cross-sectional view of the golf club head of  FIG.  49    taken along line  7 - 7  of  FIG.  49   , similar to the cross-sectional view of  FIG.  55   . 
         FIGS.  59 A- 59 D  are rear perspective views of the golf club head of  FIG.  49    including different embodiments of a badge as disclosed herein. 
         FIG.  60 A- 60 D  are cross-sectional views of the golf club head of  FIG.  49    including a filler material as disclosed herein. 
     
    
    
     For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the golf clubs and their methods of manufacture. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the golf clubs and their methods of manufacture. The same reference numerals in different figures denote the same elements. 
     The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of golf clubs and methods of manufacture described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “contain,” “include,” and “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. 
     The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “side,” “under,” “over,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of golf clubs and methods of manufacture described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in a physical, mechanical, or other manner. 
     DESCRIPTION OF EXAMPLES OF EMBODIMENTS 
     Various embodiments of the golf club heads with energy storage characteristics include a golf club head comprising a hollow body. The hollow body comprises a strikeface, a heel region, a toe region opposite the heel region, a sole, and a crown. In many embodiments, the crown comprises an upper region comprising a top rail, and a lower region. In some embodiments, a cavity is located below the top rail, is located above the lower region of the crown, and is defined at least in part by the upper and lower regions of the crown. In many embodiments, the cavity comprises a top wall, a back wall, a bottom incline, a back cavity angle measured between the top and back walls of the cavity, and at least one channel. 
     Some embodiments include a golf club comprising a hollow-bodied golf club and a shaft coupled to the hollow-bodied golf club head. The hollow-bodied golf club head comprises a strikeface, a heel region, a toe region opposite the heel region, a sole, and a crown. In many embodiments, the crown comprises an upper region comprising a top rail, and a lower region. In some embodiments, a cavity is located below the top rail, is located above the lower region of the crown, and is defined at least in part by the upper and lower regions of the crown. In many embodiments, the cavity comprises a top wall, a back wall, a bottom incline, a back cavity angle measured between the top and back walls of the cavity, and at least one channel. 
     Other embodiments include a method for manufacturing a golf club head. In many embodiments, the method comprises providing a body. The body having a strikeface, a heel region, a toe region opposite the heel region, a sole, and a crown. The crown comprises an upper region comprising a top rail and a lower region. In some embodiments, a cavity is located below the top rail, above the lower region of the crown, and is defined at least in part by the upper and lower regions of the crown. In many embodiments, the cavity comprises a top wall, a back wall adjacent to the top wall, a bottom incline adjacent to the back wall, a back cavity angle measured between the top and back walls of the cavity, and at least one channel. 
     Various embodiments include a golf club head comprising a hollow body. The hollow body comprises a strikeface, a heel region, a toe region opposite the heel region, a sole, and a crown. In many embodiments, the crown comprises an upper region comprising a top rail, and a lower region comprising a lower exterior wall. In some embodiments, a cavity is located below the top rail, is located above the lower region of the crown, and is defined at least in part by the upper and lower regions of the crown. In many embodiments, the cavity comprises a top wall, a back wall, a first inflection point adjacent the top wall and the back wall, a bottom incline, a second inflection point adjacent to the back wall and the bottom incline, a third inflection point adjacent to the bottom incline and the lower exterior wall, a lower angle measured from between the bottom incline and the lower exterior wall, the lower angle is less than 180 degrees, a back cavity angle measured between the top and back walls of the cavity, and at least one channel. 
     Some embodiments include a golf club comprising a hollow-bodied golf club and a shaft coupled to the hollow-bodied golf club head. The hollow-bodied golf club head comprises a strikeface, a heel region, a toe region opposite the heel region, a sole, and a crown. In many embodiments, the crown comprises an upper region comprising a top rail, and a lower region comprising a lower exterior wall. In some embodiments, a cavity is located below the top rail, is located above the lower region of the crown, and is defined at least in part by the upper and lower regions of the crown. In many embodiments, the cavity comprises a top wall, a back wall, a first inflection point adjacent the top wall and the back wall, a bottom incline, a second inflection point adjacent to the back wall and the bottom incline, a third inflection point adjacent to the bottom incline and the lower exterior wall, a lower angle measured from between the bottom incline and the lower exterior wall, the lower angle is less than 180 degrees, a back cavity angle measured between the top and back walls of the cavity, and at least one channel. 
     Other embodiments include a method for manufacturing a golf club head. In many embodiments, the method comprises providing a body. The body having a strikeface, a heel region, a toe region opposite the heel region, a sole, and a crown. The crown comprises an upper region comprising a top rail and a lower region comprising a lower exterior wall. In some embodiments, a cavity is located below the top rail, above the lower region of the crown, and is defined at least in part by the upper and lower regions of the crown. In many embodiments, the cavity comprises a top wall, a back wall, a first inflection point adjacent the top wall and the back wall, a bottom incline, a second inflection point adjacent to the back wall and the bottom incline, a third inflection point adjacent to the bottom incline and the lower exterior wall, a lower angle measured from between the bottom incline and the lower exterior wall, the lower angle is less than 180 degrees, a back cavity angle measured between the top and back walls of the cavity, and at least one channel. 
     Some embodiments include a golf club head including a body comprising a partial back cavity located in an interior of the body. The club head, includes a faceplate coupled to the body at a front end, defining a striking surface or strike face, and a cover or badge coupled to the body at a back end, opposite the front end. In some embodiments, as described below, the badge may be a partial badge, or the badge may be omitted entirely from the club head. In addition to the front end and the back end, the body includes a heel region, a toe region opposite the heel region, a sole, and a top rail opposite the sole. The partial back cavity contributes to a dynamic deflection or spring effect of the body when striking a golf ball. 
     Other examples and embodiments are further disclosed herein. Such examples and embodiments may be found in the figures, in the claims, and/or in the present description. 
     Golf Club Head with Back Cavity 
     In one embodiment, the golf club head has a back cavity located in an upper crown area of the golf club. In many embodiments, the back cavity can provide a box spring affect when striking a golf ball. The back cavity can be combined with varying thicknesses of the internal radius of the sole of the club head (cascading sole) to provide a spring like effect. 
     Some embodiments are directed to a club head (hybrid or fairway wood or iron with hollow design) that features a hollowed construction club head that provides a more “iron-like” look and feel. In some embodiments, the golf club head can feature a flat strikeface and iron-like profile, which can provide improved workability and accuracy, similar to an iron. A back cavity located below a top rail and along the upper crown of the club head has been designed for hybrids, fairway woods and irons with a hollow construction. The back cavity may be a full channel from the heel to the toe just below the top rail and along the upper crown or back portion of the club head. The top rail and the cavity may be any design. In some embodiments, the cavity is angled at approximately 90 degrees and provides a targeted hinge point in the crown region of the golf club head. This hinge or buckling region enables the top rail to absorb more of the impact force over a wider volumetric area causing the cavity and the top rail to act as a springboard by returning more recoiled force back to the strikeface as it returns to its original orientation thereby imparting more force into the ball. This greater club face deflection by the cavity design can lead to less spin, a higher loft angle of the golf ball upon impact, and greater ball speed with the same club speed over standard golf club heads. 
     In a standard hybrid club head, the top rail and upper crown regions do not have a cavity of this design. In comparison to the present disclosure, there is less club strikeface bending or deflection in such a standard hybrid club head. Standard hybrids are unable to have as great a spring-back effect because less energy is transferred to the top rail of the club due to the lack of a cavity. The disclosed golf club head with back cavity allows more of the impact force of the golf ball to be absorbed and then returned to the strikeface. In many embodiments, the angle of the cavity can provide a buckling point, or plastic hinge, or targeted hinge, for the strikeface to deflect more over the standard golf club. 
     The recoiling effect of the cavity on the strikeface provides: (1) a higher golf ball speed relative to the same club head speed of a club head with an upper crown cavity (or back cavity) and one without, due in part to the spring effect that is transferred from the hinged region to the strikeface to the ball; (2) less spin of the golf ball after impact with the club, due in part to the hinge point above the cavity counters more force being absorbed by the club and instead transfers more force to the ball thereby preventing the ball from spinning backward off the strikeface; and/or (3) a higher loft angle to the golf ball upon impact, due to the hinge and strikeface acting as a diving board or catapult to the ball. In some embodiments, the cavity may provide an increase in ball speed of approximately 1.0-1.2%, and an increase in launch angle of approximately 0.4-0.7 degrees. 
     Turning back to the drawings,  FIG.  1    illustrates a back toe-side perspective view of an embodiment of golf club head  1000  and  FIG.  2    illustrates a back heel-side perspective view of golf club head  1000  according to the embodiment of  FIG.  1   . Golf club head  1000  can be a hybrid-type golf club head. In other embodiments, golf club head  1000  can be an iron-type golf club head or a fairway wood-type golf club head. In many embodiments, golf club head  1000  does not include a badge or a custom tuning port. 
     Golf club head  1000  comprises a body  1001 . In many embodiments, the body is hollow. In some embodiments, the body is at least partially hollow. Body  1001  comprises a strikeface  1012 , a heel region  1002 , a toe region  1004  opposite heel region  1002 , a sole  1006 , and a crown  1008 . Crown  1008  comprises an upper region  1011  and a lower region  1013 . Upper region  1011  comprises a top rail  1015 . The top rail  1015  begins in the toe region  1004 , adjacent a top edge of the strikeface  1012 , and extends along the top of the golf club head  1000  towards the heel region  1002 . From a cross-sectional side view, such as in  FIG.  3   , the top rail  1015  begins at the transition between the strikeface  1012  and a top of the golf club head  1000  and ends at the transition between the top of the crown  1008  of the golf club head  1000  and a section of the crown with a different orientation, such as a rear wall  1023 . In some embodiments, top rail  1015  can be a flatter and taller top rail than in irons known to one skilled in the art. The flatter and taller top rail can compensate for mishits on strikeface  1012  to increase playability off the tee. 
     In some embodiments, body  1001  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S), an aluminum alloy, or a composite material. In some embodiments, strikeface  1012  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S), an aluminum alloy, or a composite material. In some embodiments, body  1001  can comprise the same material as strikeface  1012 . In some embodiments, body  1001  can comprise a different material than strikeface  1012 . 
     In many embodiments, a cavity  1030  is located below top rail  1015 . In many embodiments, cavity  1030  comprises a top rail box spring design. In many embodiments, top rail  1015  and cavity  1030  provide an increase in the overall bending of strikeface  1012 . In some embodiments, the bending of strikeface  1012  can allow for an approximately 2% to approximately 5% increase of energy. The cavity  1030  allows for the strikeface  1012  to be thinner and allow additional overall bending. For some fairway wood-type golf club head embodiments, cavity  1030  can be a reverse scoop or indentation of crown  1008  with body  1001  comprising a greater thickness or width toward sole  1006 . 
     Referring to  FIG.  1    in some embodiments, golf club head  1000  can further comprise an insert  1062  at lower region  1013  of crown  1008  towards toe region  1004 . Some embodiments comprise an internal weight at sole  1006 . In many embodiments, insert  1062  may be comprised of tungsten or some other high density material. In many embodiments, the insert shifts the center of gravity (CG) back from strikeface  1012  by approximately 0.04 inch (1 mm) to 0.10 inch (2.5 mm) and provides a 3.5% to 5.5% increase in launch angle, which can lead to an increase of playability off the tee and high or low mishits. 
     In many embodiments, the CG is in lower region  1013  of crown  1008 , close to the intersection of toe region  1004  and sole  1006 . In some embodiments, the CG of golf club head  1000  is 0.597 inches along the CGy plane and 0.541 inches along the CGz plane. For the moment of inertia, Ixx, there was a 20.5% increase over the G30 iron and a 28% increase over the Rapture DI by golf club head  1000 . For Iyy, there was a 1.7% increase over the G30 iron and a 22% increase over Rapture DI. 
     In some embodiments, approximately 3 grams (g) to approximately 4 g is added to top rail  1015 . In most embodiments, the overall mass of golf club head  1000  remains the same. In some embodiments, mass can be removed from sole  1006  or toe region  1004  to offset the addition of mass to top rail  1015 . In some embodiments, adding the approximately 3 g to approximately 4 g of mass to top rail  1015  can assist in the golf club head resisting turning. In some embodiments, the CG of the golf club head is slightly raised. 
       FIG.  3    illustrates a cross-section of golf club head  1000  along the cross-sectional line XII-XII in  FIG.  1   , according to one embodiment. As seen in  FIG.  3   , strikeface  1012  comprises a high region  1076 , a middle region  1074 , and a low region  1072 . In many embodiments, upper region  1011  of crown  1008  comprises the rear wall  1023 , a top wall  1017  of cavity  1030  below and adjacent to rear wall  1023 , and a back wall  1019  of cavity  1030  below and adjacent to top wall  1017 . 
     In some embodiments, a height  1280  of rear wall  1023  of the upper region  1011  of crown  1008  can be approximately 0.125 inch (0.318 cm) to approximately 0.75 inch (1.91 cm), or approximately 0.150 inch (0.381 cm) to approximately 0.400 inch (1.02 cm). For example, in some embodiments, the height  1280  of rear wall  1023  of the upper region  1011  of crown  1008  can be approximately 0.175 inch (0.445 cm), 0.275 inch (0.699 cm), 0.375 inch (0.953 cm), 0.475 inch (1.21 cm), 0.575 inch (1.46 cm), or 0.675 inch (1.71 cm). In some embodiments, the height  1280  of rear wall  1023  of the upper region  1011  of crown  1008  can be approximately 5% to approximately 25% of the height of golf club head  1000 . In some embodiments, the length of top rail  1015 , measured from heel region  1002  to toe region  1004 , can be approximately 70% to approximately 95% of the length of golf club head  1000 . 
     The height  1280  of rear wall  1023  of the upper region  1011  of crown  1008 , as described herein, allows cavity  1030  to absorb at least a portion of the stress on strikeface  1012  during impact with a golf ball. A golf club head having a rear wall height greater than the rear wall height  1280  described herein would absorb less stress (and allow less strikeface deflection) on impact than the golf club head  1000  described herein, due to increased dispersion of the impact stress along the top rail prior to reaching the cavity. 
     In some embodiments, cavity  1030  is located above lower region  1013  of crown  1008  and is defined at least in part by upper region  1011  and lower region  1013  of crown  1008 . Cavity  1030  comprises a top wall  1017 , a back wall  1019 , and a bottom incline  1021 . A first inflection point  1082  is located between top wall  1017  of cavity  1030  and rear wall  1019  of cavity. A second inflection point  1086  is located between rear wall  1019  of cavity  1030  and bottom incline  1021 . 
     The top wall  1017  and the rear wall  1019  of the external cavity  1030  hinge about the first inflection point  1082 . This hinge-like mobility at the first inflection point  1082  allows greater strikeface  1012  deflection. 
     In some embodiments, the height of back wall  1019 , measured from first inflection point  1082  to second inflection point  1086 , can be approximately 0.010 inch (0.25 mm) to approximately 0.138 inch (3.5 mm), or approximately 0.010 inch (0.25 mm) to approximately 0.059 inch (1.5 mm). For example, the height of back wall  1019  can be approximately 0.01 inch (0.25 mm), 0.02 inch (0.5 mm), 0.03 inch (0.75 mm), 0.04 inch (1.0 mm), 0.05 inch (1.25 mm), 0.06 inch (1.5 mm), 0.07 inch (1.75 mm), 0.08 inch (2.0 mm), 0.09 inch (2.25 mm), 0.10 inch (2.5 mm), 0.11 inch (2.75 mm), 0.012 inch (3.0 mm), 0.13 inch (3.25 mm), or 0.14 inch (3.5 mm). In many embodiments, an apex of top wall  1017  can be approximately 0.125 inch (0.318 cm) to approximately 1.25 inches (3.18 cm) or approximately 0.25 inch (0.635 cm) to approximately 1.25 inches (3.18 cm) below an apex of top rail  1015 . For example, the apex of top wall  1017  can be approximately 0.125 inch (0.318 cm), 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch (1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), or 1.25 inches (3.18 cm) below the apex of top rail  1015 . 
     In many embodiments, back wall  1019  of cavity  1030  can be substantially parallel to strikeface  1012 . In other embodiments, back wall  1019  is not substantially parallel to strikeface  1012 . In many embodiments, top wall  1017  of cavity is angled toward strikeface  1012  when moving toward the first inflection point  1082 . This orientation of top wall  1017  creates a buckling point or hinge point or plastic hinge to direct the stress of impact toward cavity  1030  and allowing increased flexing of strikeface  1012  during impact. 
     Lower region  1013  of crown  1008  comprises bottom incline  1021  of cavity  1030 . In many embodiments, the second inflection point  1086 , adjacent to bottom incline  1021 , can be at least approximately 0.25 inch (0.635 cm) to approximately 2.0 inches (5.08 cm), or approximately 0.5 inch (1.27 cm) to approximately 1.5 inches (3.81 cm) below the apex of top rail  1015 . For example, the second inflection point  1086  can be at least approximately 0.25 inch (0.635 cm), 0.5 inch (1.27 cm), 0.75 inch (1.91 cm), 1.0 inch (2.53 cm), 1.25 inches (3.18 cm), 1.5 inches (3.81 cm), 1.75 inches (4.45 cm) or 2.0 inches (5.08 cm) below the apex of top rail  1015 . In some embodiments, the maximum height of the bottom incline, measured from the sole  1006  of the club head  1000  to the second inflection point  1086 , can be at least approximately 0.25 inch (0.635 cm) to approximately 3 inches (7.62 cm), or approximately 0.50 inch (1.27 cm) to approximately 2 inches (5.08 cm) above a lowest point of the sole  1006 . For example, the second inflection point  1086  can be at least approximately 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch (1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), 1.25 inches (3.18 cm), 1.375 inches (3.49 cm), 1.5 inches (3.81 cm), 1.625 inches (4.12 cm), 1.75 inches (4.45 cm), 1.875 inches (4.76 cm), 2.0 inches (5.08 cm), 2.125 inches 5.40 cm), 2.25 inches (5.71 cm), 2.375 inches (6.03 cm), 2.5 inches (6.35 cm), 2.625 inches (6.67 cm), 2.75 inches (7.00 cm), 2.875 inches (7.30 cm), or 3.0 inches (7.62 cm) above a lowest point of the sole. 
     Cavity  1030  further comprises at least one channel  1039  ( FIG.  1   ). In many embodiments, channel  1039  extends from heel region  1002  to toe region  1004 . A channel width  1032  ( FIG.  3   ) can be substantially constant throughout channel  1039 . In some embodiments, channel width  1032  ( FIG.  3   ) can be approximately 0.008 inch (0.2 mm) to approximately 1 inch (25 mm), or approximately 0.008 inch (0.2 mm) to approximately 0.31 inch (8 mm). For example, channel width  1032  can be approximately 0.008 inch (0.2 mm), 0.016 inch (0.4 mm), 0.024 inch (0.6 mm), 0.031 inch (0.8 mm), 0.039 inch (1.0 mm), 0.079 inch (2 mm), 0.12 inch (3 mm), 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.39 inch (10 mm), 0.59 inch (15 mm), 0.79 inch (20 mm), or 0.98 inch (25 mm). In other embodiments, a channel toe region width of channel  1039  is smaller than a channel heel region width of channel. In other embodiments, the channel heel region width is smaller than the channel toe region width. In other embodiments, a channel middle region width of channel  1039  can be smaller than at least one of the channel heel region width or the channel toe region width. In other embodiments, the channel middle region width can be greater than at least one of the channel heel region width or the channel toe region width. In some embodiments, channel  1039  is symmetrical. In other embodiments, channel  1039  is non-symmetrical. In other embodiments, channel  1039  can further comprise at least two partial channels. In some embodiments, channel  1039  can comprise a series of partial channels interrupted by one or more bridges. In some embodiments, the one or more bridges can be approximately the same thickness as the thickness of upper region  1011  of crown  1008 . 
     The channel width  1032 , as described herein, allows absorption of stress from strikeface  1012  on impact. A golf club head having a channel width less than the channel width described herein (e.g. a golf club head with a less pronounced cavity) would allow less stress absorption from the strikeface on impact (due to less material on the upper region  1011  of crown  1008 ), and therefore would experience less strikeface deflection than the golf club head  1000  described herein. 
     In many embodiments, cavity  1030  further comprises a back cavity angle  1035 . Back cavity angle is measured between top wall  1017  and back wall  1019  of cavity  1030 . In many embodiments, back cavity angle  1035  can be approximately 70 degrees to approximately 110 degrees. In some embodiments, back cavity angle  1035  can be approximately 80 degrees to approximately 100 degrees. In some embodiments, back cavity angle  1035  is approximately 70, 75, 80, 85, 90, 95, 100, or 110 degrees. In many embodiments, back cavity angle  1035  provides a buckling point or plastic hinge or targeted hinge at a top rail hinge point  1070 , upon golf club head  1000  impacting the golf ball. In some embodiments, the wall thickness at top rail hinge point  1070  is thinner than at top wall  1017  of cavity  1030   
       FIG.  4    illustrates a view of crown  1008  of the cross-section of golf club head  1000  of  FIG.  3    alongside a similar cross-section of a golf club head  1200  without a cavity along a similar cross-sectional line XII-XII in  FIG.  1   . Golf club head  1200  comprises a strikeface  1212 , a crown  1208 , a top rail  1215 , a top rail hinge point  1270 , and a rear wall  1223 . In many embodiments, golf club head  1000  comprises a rear angle  1040 , a top rail angle  1045 , and a strikeface angle  1050 . Upper region angle  1040  is measured from top wall  1017  to rear wall  1023  of upper region  1011 . In many embodiments, rear angle  1040  can be approximately 70 degrees to approximately 110 degrees. In some embodiments, rear angle  1040  is approximately 90 degrees. Top rail angle  1045  is measured from rear wall  1023  of upper region  1011  to top rail  1015 . In many embodiments, top rail angle  1045  can be approximately 35 degrees to approximately 120 degrees or 70 degrees to approximately 110 degrees. In some embodiments, top rail angle  1045  can be approximately 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, or 120 degrees. Strikeface angle  1050  is measured from strikeface  1012  to top rail  1015 . In many embodiments, strikeface angle  1050  can be approximately 70 degrees to approximately 160 degrees or 70 degrees to approximately 110 degrees. In some embodiments, strikeface angle  1050  is approximately 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, or 160 degrees. 
     Referring to  FIG.  4   , in some embodiments, a minimum gap  1090  between strikeface  1012  and back wall  1019  is approximately 0.079 inch (2 mm) to approximately 0.39 inch (10 mm). For example, the minimum gap  1090  between strikeface  1012  and back wall  1019  can be approximately 0.079 inch (2 mm), 0.16 inch (4 mm), 0.24 inch (6 mm), 0.31 inch (8 mm), or 0.39 inch (10 mm). In some embodiments, the minimum gap  1090  between the strikeface  1012  and back wall  1019  is less than approximately 0.55 inch (14 mm), less than approximately 0.47 inch (12 mm), less than approximately 0.39 inch (10 mm), less than approximately 0.31 inch (8 mm), less than approximately 0.24 inch (6 mm), or less than approximately 0.16 inch (4 mm). Further, in some embodiments, a maximum gap between strikeface  1012  and rear wall  1023  of upper region  1011  of golf club head  1000  is greater than minimum gap  1090 . Further still, in some embodiments, a maximum gap between strikeface  1012  and bottom incline  1021  in lower region  1013  of golf club head  1000  is greater than minimum gap  1090  and maximum gap in upper region  1011 . 
     In many embodiments, cavity  1030  can provide an increase in golf ball speed over golf club head  1200  or other standard golf club heads, can reduce the spin rate of standard hybrids club heads, and can increase the launch angle over both the standard hybrid and iron club heads. In many embodiments, the shape of cavity  1035  determines the level of spring and timing of the response of golf club head  1000 . When the golf ball impacts strikeface  1012  of club head  1000  with cavity  1030 , strikeface  1012  springs back like a drum, and crown  1008  bends in a controlled buckle manner. In many embodiments, top rail  1015  can absorb more stress over greater volumetric space than a top rail in a golf club head without cavity  1030 . The length, depth and width of cavity  1030  can vary. These parameters provide control regarding how much spring back is present in the overall design of club head  1000 . 
     Upon impact with the golf ball, strikeface  1012  can bend inward at a greater distance than on a golf club without cavity  1030 . In some embodiments, strikeface  1012  has an approximately 10% to approximately 50% greater deflection than a strikeface on a golf club head without cavity  1030 . In some embodiments, strikeface  1012  has an approximately 5% to approximately 40% or approximately 10% to approximately 20% greater deflection than a strikeface on a golf club head without cavity  1035 . For example, strikeface  1012  can have an approximately 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40% greater deflection than a strikeface on a golf club head without cavity  1035 . In many embodiments, there is both a greater distance of retraction by strikeface  1012  due to the hinge and bending of cavity  1030  over a standard strikeface that does not have a back portion of the club without the cavity. 
     In many embodiments, the face deflection is greater with club head  1000  having cavity  1030 , as a greater buckling occurs along top rail hinge point  1070  upon impact with the golf ball. Cavity  1030 , however, provides a greater dispersion of stress along top rail hinge point  1070  region of the top rail and the spring back force is transferred from cavity  1030  and top rail  1015  to strikeface  1012 . A standard top rail without a cavity does not have this hinge/buckling effect, nor does it absorb a high level of stress over a large volumetric area of the top rail. Therefore, the standard strikeface does not contract and then recoil as much as strikeface  1012 . Further, both a larger region of strikeface  1012  and top rail  1015  absorb more stress than the same crown region of a standard golf club head with a standard top rail and no cavity. In many embodiments, although there is greater stress along a greater area above cavity  1030  than the same area in a standard club without the cavity, the durability of the club head with and without the cavity is the same. By adding more spring to the back end of the club (due to the inward inclination of top wall  1017  toward strikeface  1012 ), more force is displaced throughout the volume of the structure. The stress is observed over a greater area of strikeface  1012  and top rail  1015  of golf club head  1000 . Peak stresses can be seen in the standard top rail club head. However, more peak stresses are seen in golf club head  1000  but distributed over a large volume of the material. The hinge and bend regions of golf club head  1000  (i.e., the region above cavity  1030  and cavity  1030  itself) will not deform as long as the stress does not meet the critical buckling threshold. Cavity  1030  and its placement can be designed to be under the critical K value of the buckling threshold. 
     Turning ahead in the drawings,  FIG.  8    illustrates a back perspective view of an embodiment of golf club head  2200  and  FIG.  9    illustrates a back heel-side perspective view of golf club head  2200  according to the embodiment of  FIG.  8   . In some embodiments, golf club head  2200  can be similar to golf club head  1000  ( FIG.  1   ). Golf club head  2200  can be a hybrid-type golf club head. In other embodiments, golf club head  2200  can be an iron-type golf club head or a fairway wood-type golf club head. In many embodiments, golf club head  2200  does not include a badge or a custom tuning port. 
     Golf club head  2200  comprises a body  2201 . In some embodiments, body  2201  can be similar to body  1001  ( FIG.  1   ). In many embodiments, the body is hollow. In some embodiments, the body is at least partially hollow. Body  2201  comprises a strikeface  2212 , a heel region  2202 , a toe region  2204  opposite heel region  2202 , a sole  2206 , and a rear  2210 . Rear  2210  comprises an upper region  2211  and a lower region  2213 . Upper region  2211  comprises a top rail  2215 . The top rail  2215  can be similar to the top rail  1015  of golf club head  1000 . In some embodiments, top rail  2215  can be a flatter and taller top rail than in the in irons known to one skilled in the art. The flatter and taller top rail can compensate for mis-hits on strikeface  2212  to increase playability off the tee. 
     Body  2201  of  FIGS.  8 - 12    further comprises a blade length. The blade length for body  2201  can be measured similar to blade length  3725  as shown and described in  FIG.  29    (i.e., a measurement parallel to the flat surface of the strikeface  3712 , from a toe edge  3726  of the strikeface  3712 , to strikeface end  3727  right before the strikeface  3712  integrally curves into the hosel). The blade length of the body  2201  can range from 2.80 inch (7.11 cm) to 3.00 inch (7.62 cm). For example, in some embodiments, the body  2201  can comprise a blade length of 2.80 inch (7.11 cm), 2.82 inch (7.16 cm), 2.84 inch (7.21 cm), 2.86 inch (7.26 cm), 2.88 inch (7.32 cm), 2.90 inch (7.37 cm), 2.93 inch (7.44 cm), 2.94 inch (7.47 cm), 2.96 inch (7.52 cm), 2.98 inch (7.57 cm), or 3.00 inch (7.62 cm). 
     The body  2201  further comprises a uniform thinned region transitioning from the bottom of the strikeface  2212  to the sole  2206 , toward a cascading sole portion of the sole (as described in greater detail below). In the illustrated embodiment, the uniform thinned region comprises a sole thickness measured perpendicular from the exterior surface  2225  to the interior surface at the uniform thinned region, which can remain constant from the bottom of the strikeface  2212  to adjacent the cascading sole portion of the sole. In some embodiments, the sole thickness of the uniform thinned region can be thinner than a conventional sole. For example, in some embodiments, the sole thickness of the uniform thinned region may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness of the uniform thinned region may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness of the uniformed thinned region can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
     In some embodiments, body  2201  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, body  2201  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, strikeface  2212  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, strikeface  2212  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, body  2201  can comprise the same material as strikeface  2212 . In some embodiments, body  2201  can comprise a different material than strikeface  2212 . 
     In many embodiments, a cavity  2230  is located below top rail  2215 . In some embodiments, the length of top rail  2215 , measured from heel region  2202  to toe region  2204 , can be approximately 70% to approximately 95% of the length of golf club head  2200 . In many embodiments, cavity  2230  comprises a top rail box spring design. In many embodiments, top rail  2215  and cavity  2230  provide an increase in the overall bending of strikeface  2212 . In some embodiments, the bending of strikeface  2212  can allow for an approximately 2% to approximately 5% increase of energy. The cavity  2230  allows for the strikeface  2212  to be thinner and allow additional overall bending. For some fairway wood-type golf club head embodiments, cavity  2230  can be a reverse scoop or indentation of rear  2210  with body  2201  comprising a greater thickness or width sole  2206 . 
       FIG.  10    illustrates a cross-section of golf club head  2200  along the cross-sectional line XXIV-XXIV in  FIG.  8   , according to one embodiment. As seen in  FIG.  10   , strikeface  2212  comprises a high region  2476 , a middle region  2474 , and a low region  2472 . In many embodiments, upper region  2211  of rear  2210  comprises a rear wall  2423 , a top wall  2417  of cavity  2230  below and adjacent to rear wall  2423 , and a back wall  2219  of cavity  2230  below and adjacent to top wall  2417 . In some embodiments, a top wall length  2491  of top wall  2417  can be approximately 0.090 inch (0.229 cm) to approximately 0.130 inch (0.330 cm). In some embodiments, top wall length  2491  of top wall  2417  can be approximately 0.090 inch (0.229 cm), 0.100 inch (0.254 cm), 0.110 inch (0.279 cm), 0.120 inch (0.305 cm), or 0.130 inch (0.330 cm). 
     In some embodiments, a height  2480  of rear wall  2423  of the upper region  2211  of rear  2210  can be approximately 0.125 inch (0.318 cm) to approximately 0.75 inch (1.91 cm), or approximately 0.150 inch (0.381 cm) to approximately 0.400 inch (1.02 cm). For example, in some embodiments, the height  2480  of rear wall  2423  of the upper region  2211  of rear  2210  can be approximately 0.175 inch (0.445 cm), 0.275 inch (0.699 cm), 0.375 inch (0.953 cm), 0.475 inch (1.21 cm), 0.575 inch (1.46 cm), or 0.675 inch (1.71 cm). In some embodiments, the height  2480  of rear wall  2423  of the upper region  2211  of rear  2210  can be approximately 0.180 inch (0.4572 cm) to approximately 0.200 inch (0.508 cm). In some embodiments, the height  2480  of rear wall  2423  of the upper region  2211  of rear  2210  can be approximately 0.190 inch (0.4826 cm). In some embodiments, the height  2480  of rear wall  2423  of the upper region  2211  of rear  2210  can be approximately 5% to approximately 25% of the height of golf club head  2200 . 
     The height  2480  of rear wall  2423  of the upper region  2211  of rear  2210 , as described herein, allows cavity  2230  to absorb at least a portion of the stress on strikeface  2212  during impact with a golf ball. A golf club head having a rear wall height greater than rear wall height  2480  described herein would absorb less stress (and allow less strikeface deflection) on impact than the golf club head  2200  described herein, due to increased dispersion of the impact stress along the top rail prior to reaching the cavity. 
     In some embodiments, cavity  2230  is located above a lower region  2213  of rear  2210  and is defined at least in part by upper region  2211  and lower region  2213  of rear  2210 . Cavity  2230  comprises the top wall  2417 , the back wall  2219 , and a bottom incline  2421 . A first inflection point  2482  is located between top wall  2417  of cavity  2230  and rear wall  2219  of cavity. A second inflection point  2486  is located between rear wall  2219  of cavity  2230  and bottom incline  2421 . 
     In some embodiments, a height  2488  of back wall  2219 , measured from first inflection point  2482  to second inflection point  2486 , can be approximately 0.100 inch (0.254 cm) to approximately 0.600 inch (1.524 cm). For example, height  2488  of back wall  2219  can be approximately 0.100 inch (0.254 cm), 0.150 inch (0.381 cm), 0.200 inch (0.508 cm), 0.250 inch (0.635 cm), 0.300 inch (0.762 cm), 0.350 inch (0.889 cm), 0.400 inch (1.016 cm), 0.450 inch (1.143 cm), 0.500 inch (1.27 cm), 0.550 inch (1.397 cm), or 0.600 inch (1.524 cm). In many embodiments, height  2488  of back wall  2219  can be approximately 0.420 inch (1.067 cm) to approximately 0.520 inch (1.321 cm). In some embodiments, height  2488  of back wall  2219  can be approximately 0.420 inch (1.067 cm), 0.430 inch (01.092 cm), 0.440 inch (1.118 cm), 0.450 inch (1.143 cm), 0.460 inch (1.168 cm), 0.470 inch (1.194 cm), 0.480 inch (1.219 cm), 0.490 inch (1.245 cm), 0.500 inch (1.27 cm), 0.510 inch (1.295 cm), or 0.520 inch (1.321 cm). 
     In many embodiments, an apex of top wall  2417  can be approximately 0.125 inch (0.318 cm) to approximately 1.25 inches (3.18 cm) or approximately 0.25 inch (0.635 cm) to approximately 1.25 inches (3.18 cm) below an apex of top rail  2215 . For example, the apex of top wall  2417  can be approximately 0.125 inch (0.318 cm), 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch (1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), or 1.25 inches (3.18 cm) below the apex of top rail  2215 . 
     In many embodiments, back wall  2219  of cavity  2230  can be substantially parallel to strikeface  2212 . In other embodiments, back wall  2219  is not substantially parallel to strikeface  2212 . In some embodiments, back wall  2219  of cavity  2230  is substantially parallel to rear wall  2423  of upper region  2211  of rear  2210 . In many embodiments, back wall  2219  of cavity  2230  is angled away from strikeface  2212  when moving from first inflection point  2482  to second inflection point  2486 . This orientation of back wall  2219  creates a buckling point or hinge point or plastic hinge to direct the stress of impact toward cavity  2230  and to allow increased flexing of strikeface  2212  during impact. 
     Lower region  2213  of rear  2210  comprises the bottom incline  2421  of cavity  2230  and a lower exterior wall  2427 . In some embodiments, bottom incline  2421  of cavity  2230  can have a bottom incline length  2484  measured from second inflection point  2486  to a third inflection point  2492  positioned between bottom incline  2421  and lower exterior wall  2427 . In a number of embodiments, bottom incline length  2484  can be approximately 0.150 inch (0.381 cm) to approximately 0.210 inch (0.533 cm). In many embodiments, bottom incline length  2484  can be approximately 0.150 inch (0.381 cm), 0.160 inch (0.406 cm), 0.170 inch (0.432 cm), 0.180 inch (0.457 cm), 0.190 inch (0.483 cm), 0.200 inch (0.508 cm), or 0.210 inch (0.533 cm). 
     In some embodiments, a lower angle  2451  can be measured from the between the bottom incline  2421  and the lower exterior wall  2427 . In some embodiments, lower angle  2451  can be less than 180 degrees. In a number of embodiments, lower angle  2451  can be approximately 30 degrees to less than 180 degrees. In various embodiments, lower angle  2451  can be approximately 70 degrees to approximately 130 degrees. In some embodiments, lower angle  2451  can be approximately 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, or 130 degrees. 
     In some embodiments, an inflection angle  2496  measured from back wall  2219  to bottom incline  2421  can be approximately 70 degrees to approximately 150 degrees. In some embodiments, inflection angle  2496  can be approximately 90 degrees to approximately 130 degrees. In some embodiments, inflection angle  2496  is approximately 70, 75, 80, 85, 90, 95, 100, 110, 115, 120, 125, 130, 135, 140, 145, or 150 degrees. 
     In many embodiments, second inflection point  2486 , adjacent to bottom incline  2421 , can be at least approximately 0.25 inch (0.635 cm) to approximately 2.0 inches (5.08 cm), or approximately 0.5 inch (1.27 cm) to approximately 1.5 inches (3.81 cm) below the apex of top rail  2215 . For example, the second inflection point  2486  can be at least approximately 0.25 inch (0.635 cm), 0.5 inch (1.27 cm), 0.75 inch (1.91 cm), 1.0 inch (2.53 cm), 1.25 inches (3.18 cm), 1.5 inches (3.81 cm), 1.75 inches (4.45 cm) or 2.0 inches (5.08 cm) below the apex of top rail  2215 . In some embodiments, the maximum height of the bottom incline, measured from the sole  2206  of the club head  2200  to second inflection point  2486 , can be at least approximately 0.25 inch (0.635 cm) to approximately 3 inches (7.62 cm), or approximately 0.50 inch (1.27 cm) to approximately 2 inches (5.08 cm) above a lowest point of the sole  2206 . For example, the second inflection point  2486  can be at least approximately 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch (1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), 1.25 inches (3.18 cm), 1.375 inches (3.49 cm), 1.5 inches (3.81 cm), 1.625 inches (4.12 cm), 1.75 inches (4.45 cm), 1.875 inches (4.76 cm), 2.0 inches (5.08 cm), 2.125 inches 5.40 cm), 2.25 inches (5.71 cm), 2.375 inches (6.03 cm), 2.5 inches (6.35 cm), 2.625 inches (6.67 cm), 2.75 inches (7.00 cm), 2.875 inches (7.30 cm), or 3.0 inches (7.62 cm) above a lowest point of the sole. 
     Cavity  2230  further comprises at least one channel  2239  ( FIG.  8   ). In many embodiments, channel  2239  extends from heel region  2202  to toe region  2204 . A channel width  2432  ( FIG.  10   ) measured from back wall  2219  ( FIG.  10   ) to rear wall  2423  ( FIG.  10   ) and substantially perpendicular to a ground plane when golf club head  2200  is at address, can be substantially constant throughout channel  2239 . In some embodiments, channel width  2432  ( FIG.  10   ) can be approximately 0.008 inch (0.2 mm) to approximately 1 inch (25 mm), or approximately 0.008 inch (0.2 mm) to approximately 0.31 inch (8 mm). For example, channel width  2432  can be approximately 0.008 inch (0.2 mm), 0.016 inch (0.4 mm), 0.024 inch (0.6 mm), 0.031 inch (0.8 mm), 0.039 inch (1.0 mm), 0.079 inch (2 mm), 0.12 inch (3 mm), 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.39 inch (10 mm), 0.59 inch (15 mm), 0.79 inch (20 mm), or 0.98 inch (25 mm). In other embodiments, a channel toe region width of channel  2239  is smaller than a channel heel region width of channel. In other embodiments, the channel heel region width is smaller than the channel toe region width. In other embodiments, a channel middle region width of channel  2239  can be smaller than at least one of the channel heel region width or the channel toe region width. In other embodiments, the channel middle region width can be greater than at least one of the channel heel region width or the channel toe region width. In some embodiments, channel  2239  is symmetrical from heel region  2202  to toe region  2204 . In other embodiments, channel  2239  is non-symmetrical. In other embodiments, channel  2239  can further comprise at least two partial channels. In some embodiments, channel  2239  can comprise a series of partial channels interrupted by one or more bridges. In some embodiments, the one or more bridges can be approximately the same thickness as the thickness of upper region  2211  of rear  2210 . 
     The channel width  2432 , as described herein, allows absorption of stress from strikeface  2212  on impact. A golf club head having a channel width less than the channel width described herein (e.g. a golf club head with a less pronounced cavity) would allow less stress absorption from the strikeface on impact (due to less material on the upper region  2211  of rear  2210 ), and therefore would experience less strikeface deflection than the golf club head  2200  described herein. 
     In many embodiments, cavity  2230  further comprises a back cavity angle  2435 . Back cavity angle is measured between top wall  2417  and back wall  2219  of cavity  2230 . In many embodiments, back cavity angle  2435  can be approximately 70 degrees to approximately 110 degrees. In some embodiments, back cavity angle  2435  can be approximately 80 degrees to approximately 100 degrees. In some embodiments, back cavity angle  2435  is approximately 70, 75, 80, 85, 90, 95, 100, or 110 degrees. In many embodiments, back cavity angle  2435  provides a buckling point or plastic hinge or targeted hinge at a top rail hinge point  2470 , upon golf club head  2200  impacting the golf ball at strike face  2212 . In some embodiments, the wall thickness at top rail hinge point  2470  is thinner than at top wall  2417  of cavity  2230   
       FIG.  11    illustrates a view of top rail  2215  and a portion of rear  2210  of the cross-section of golf club head  2200  of  FIG.  8    different from cross-section of golf club head  1200  as shown in  FIG.  4   . In many embodiments, golf club head  2200  comprises a rear angle  2540 , a top rail angle  2545 , and a strikeface angle  2550 . Rear angle  2540  is measured from top wall  2417  to rear wall  2423  of upper region  2211 . In many embodiments, rear angle  2540  can be approximately 70 degrees to approximately 110 degrees. In some embodiments, rear angle  2540  is approximately 70, 75, 80, 85, 90, 95, 100, 105, or 110 degrees. Top rail angle  2545  is measured from rear wall  2423  of upper region  2211  to top rail  2215 . In many embodiments, top rail angle  2545  can be approximately 35 degrees to approximately 120 degrees or 70 degrees to approximately 110 degrees. In some embodiments, top rail angle  2545  can be approximately 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, or 120 degrees. Strikeface angle  2550  is measured from strikeface  2212  to top rail  2215 . In many embodiments, strikeface angle  2550  can be approximately 70 degrees to approximately 160 degrees or 70 degrees to approximately 110 degrees. In some embodiments, strikeface angle  2550  is approximately 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, or 160 degrees. 
     In some embodiments, a minimum gap  2590  measured perpendicularly to the strikeface  2212  to the back wall  2219  is approximately 0.079 inch (2 mm) to approximately 0.39 inch (10 mm). For example, the minimum gap  2590  between strikeface  2212  and back wall  2219  can be approximately 0.079 inch (2 mm), 0.16 inch (4 mm), 0.24 inch (6 mm), 0.31 inch (8 mm), or 0.39 inch (10 mm). In some embodiments, the minimum gap  2590  between the strikeface  2212  and back wall  2219  is less than approximately 0.55 inch (14 mm), less than approximately 0.47 inch (12 mm), less than approximately 0.39 inch (10 mm), less than approximately 0.31 inch (8 mm), less than approximately 0.24 inch (6 mm), or less than approximately 0.16 inch (4 mm). Further, in some embodiments, a maximum gap between strikeface  2212  and rear wall  2423  of upper region  2211  of golf club head  2200  is greater than minimum gap  2590 . Further still, in some embodiments, a maximum gap between strikeface  2212  and bottom incline  2421  ( FIG.  10   ) in lower region  2213  ( FIG.  10   ) of golf club head  2200  is greater than minimum gap  2590  and the maximum gap in upper region  2211 . 
       FIG.  12    illustrates a simplified cross-sectional view of golf club head  2200 , similar to the detailed cross-section of the golf club head  2200  illustrated in  FIG.  10   . Golf club head  2200  includes the cavity  2230 , an exterior surface  2225 , the upper region  2211 , and the lower region  2213 . Upper region  2211  includes rear wall  2423 , cavity  2230  includes cavity exterior wall  2225 , top wall  2417 , and back wall  221 , while the lower region  2213  includes bottom incline  2421  and lower exterior wall  2427 . In many embodiments, a maximum upper distance  2692  measured as the perpendicular distance from the exterior surface  2225  of the strikeface  2212  to the exterior surface  2225  of the rear wall  2423  of upper region  2211  can be approximately 0.20-0.59 inch (5-15 mm). For example, maximum upper distance  2692  can be approximately 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (8.89 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), 0.47 inch (12 mm), 0.51 inch (13 mm), 0.55 inch (14 mm), or 0.59 inch (15 mm). In some embodiments, maximum upper distance  2692  can be approximately 0.355 inch (9.02 mm). 
     Further, a minimum upper distance  2694  measured as the perpendicular distance from the exterior surface  2225  of the strikeface  2212  to the exterior surface  2225  of the back wall  2219  can be approximately 0.16-0.47 inch (4-12 mm). For example, minimum upper distance  2694  can be approximately 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (9 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), or 0.47 inch (12 mm). In some embodiments, minimum upper distance  2694  can be approximately 0.284 inch (7.21 mm). 
     Further still, a maximum lower distance  2696  measured as the perpendicular distance from the exterior surface  2225  of the strikeface  2212  to the exterior surface  2225  of the lower exterior wall  2427  can be approximately 0.98-1.57 inch (25-40 mm). For example, maximum lower distance  2696  can be approximately 0.98 inch (25 mm), 1.02 inch (26 mm), 1.06 inch (27 mm), 1.10 inch (28 mm), 1.14 inch (29 mm), 1.18 inch (30 mm), 1.22 inch (31 mm), 1.26 inch (32 mm), 1.30 inch (33 mm), 1.34 inch (34 mm), 1.38 inch (35 mm), 1.42 inch (36 mm), 1.46 inch (37 mm), 1.50 inch (38 mm), 1.54 inch (39 mm), 1.57 inch or (40 mm). In some embodiments, maximum lower distance  2696  can be approximately 1.043 inch (26.5 mm). In many embodiments, maximum lower distance  2696  is greater than maximum upper distance  2692 , and maximum upper distance  2692  is greater than minimum upper distance  2694 . 
     In many embodiments, cavity  2230  can provide an increase in golf ball speed over golf club head  1200  ( FIG.  11   ) or other standard golf club heads, can reduce the spin rate of standard hybrids club heads, and can increase the launch angle over both the standard hybrid and iron club heads. In many embodiments, the shape of cavity  2230  determines the level of spring and timing of the response of golf club head  2200 . When the golf ball impacts strikeface  2212  of club head  2200  with cavity  2230 , strikeface  2212  springs back like a drum, and rear  2210  bends in a controlled buckle manner. In many embodiments, top rail  2215  can absorb more stress over greater volumetric space than a top rail in a golf club head without cavity  2230 . The length, depth and width of cavity  2230  can vary. These parameters provide control regarding how much spring back is present in the overall design of club head  2200 . 
     Upon impact with the golf ball, strikeface  2212  can bend inward at a greater distance than on a golf club without cavity  2230 . In some embodiments, strikeface  2212  has an approximately 10% to approximately 50% greater deflection than a strikeface on a golf club head without cavity  2230 . In some embodiments, strikeface  2212  has an approximately 5% to approximately 40% or approximately 10% to approximately 20% greater deflection than a strikeface on a golf club head without cavity  2230 . For example, strikeface  2212  can have an approximately 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40% greater deflection than a strikeface on a golf club head without cavity  2230 . In many embodiments, there is both a greater distance of retraction by strikeface  2212  due to the hinge and bending of cavity  2230  over a standard strikeface that does not have a back portion of the club without the cavity. 
     In many embodiments, the face deflection is greater with club head  2200  having cavity  2230 , as a greater buckling occurs along top rail hinge point  2470  upon impact with the golf ball. Cavity  2230 , however, provides a greater dispersion of stress along top rail hinge point  2470  region of the top rail, and the spring back force is transferred from cavity  2230  and top rail  2215  to strikeface  2212 . A standard top rail without a cavity does not have this hinge/buckling effect, nor does it absorb a high level of stress over a large volumetric area of the top rail. Therefore, the standard strikeface does not contract and then recoil as much as strikeface  2212 . Further, both a larger region of strikeface  2212  and top rail  2215  absorb more stress than the same crown region of a standard golf club head with a standard top rail and no cavity. In many embodiments, although there is greater stress along a greater area above cavity  2230  than the same area in a standard club without the cavity, the durability of the club head with and without the cavity is the same. By adding more spring to the back end of the club (due to the inward inclination of top wall  2417  toward strikeface  2212 ), more force is displaced throughout the volume of the structure. The stress is observed over a greater area of strikeface  2212  and top rail  2215  of golf club head  2200 . Peak stresses can be seen in the standard top rail club head. However, more peak stresses are seen in golf club head  2200  but distributed over a large volume of the material. The hinge and bend regions of golf club head  2200  (i.e., the region above cavity  2230  and cavity  2230  itself) will not deform as long as the stress does not meet the critical buckling threshold. Cavity  2230  and its placement can be designed to be under the critical K value of the buckling threshold. 
     Turning to  FIG.  5   ,  FIG.  5    illustrates a golf club  1500  comprising a golf club head  1500  and a shaft  1590  coupled to golf club head  1500 . In some embodiments, golf club head  1500  of golf club  15000  comprises a hybrid-type golf club head. In other embodiments, golf club head  1500  can be an iron-type golf club head or a fairway wood-type golf club head. In many embodiments, golf club head  1500  can be similar to golf club head  100  or golf club head  1000  ( FIG.  1   ). Golf club head  1500  can be hollow-bodied and comprises a strikeface  1512 , a heel region  1502 , a toe region  1504  opposite heel region  1502 , a sole  1506 , and a crown  1508 . The crown  1508  comprises an upper region  1511  and a lower region  1513 . The upper region  1511  comprises a top rail  1515 . Golf club head  1500  further comprises a cavity  1530  located below top rail  1515  and above lower region  1513  of crown  1508 . 
       FIG.  6    illustrates a cross-section of golf club head  1500  along the cross-sectional line XVI-XVI in  FIG.  5   , according to one embodiment. In some embodiments, cavity  1530  can be defined at least in part by upper region  1511  and lower region  1513 . In many embodiments, cavity  1530  comprises a top wall  1517 , a back wall  1519 , a bottom incline  1521 , a back cavity angle  1535  measured between top wall  1517  and back wall  1519 , and at least one channel  1539 . In some embodiments, an apex of top wall  1517  is approximately 0.25 inch to approximately 1.25 inches below an apex of top rail  1515 . In some embodiments, the apex of top wall  1517  is approximately 0.375 inch below the apex of top rail  1515 . In some embodiments, bottom incline  1521  can be at least approximately 0.50 inch to approximately 2 inches below an apex of top rail  1515 . In many embodiments, back cavity angle  1535  can be approximately 70 degrees to approximately 110 degrees. In some embodiments, back cavity angle  1535  can be approximately 90 degrees. 
     In many embodiments, the upper region  1511  comprises the top and back walls of the cavity; and the lower region of the crown comprises the bottom incline of the cavity. In some embodiments, upper region  1511  further comprises a rear wall  1523  adjacent to top wall  1517  of cavity  1530  and a rear angle  1540  measured between top wall  1517  of cavity  1530  and rear wall  1523  of upper region  1511 . In many embodiments, rear angle  1540  is approximately 70 degrees to approximately 110 degrees. 
     In another embodiment, the golf club head can comprise a hosel. The hosel can comprise a hosel notch. The hosel notch can allow for iron-like range of loft and lie angle adjustability. 
     As shown in  FIG.  12   , a further deflection feature of the golf club head  2200  can be the uniform thinned region  2660 , located at the sole  2206  and stretching between the rear  2210  of the body  2201  and the strikeface  2212 , toward a cascading sole portion of the sole (as described in greater detail below). The uniform thinned region  2660  can provide multiple benefits. First, the uniform thinned region  2660  can reduce stress on the strikeface  2212  caused during impact with the golf ball. Second, the uniform thinned region  2660  can bend allowing the strikeface  2212  to experience greater deflection. Third, the uniform thinned region  2660  removes weight from the sole area, allowing the weight to be redistributed more toward the rear of the golf club head  2200 . At impact, the energy imparted to the strikeface  2212  by the golf ball can cause the uniform thinned region  2660  to bend outward, which in turn increases the strikeface  2212  deflection. After bending, the uniform thinned region  2660  rebounds back to its original position returning the majority of the energy from impact back to the golf ball. The result is the golf club head  2200  imparts increased ball speeds and greater travel distances to the golf ball after impact. 
     Turning ahead in the drawings,  FIG.  13    illustrates a back perspective view of an embodiment of golf club head  2700  and  FIG.  14    illustrates a back heel-side perspective view of golf club head  2700  according to the embodiment of  FIG.  13   . In some embodiments, golf club head  2700  can be similar to golf club head  1000  ( FIG.  1   ), and/or golf club head  2200  ( FIG.  8   ). Golf club head  2700  can be a hybrid-type golf club head. In other embodiments, golf club head  2700  can be an iron-type golf club head or a fairway wood-type golf club head. In many embodiments, golf club head  2700  does not include a badge or a custom tuning port. 
     Golf club head  2700  comprises a body  2701 . In some embodiments, body  2701  can be similar to body  1001  ( FIG.  1   ), and/or body  2201  ( FIG.  8   ). In many embodiments, the body is hollow. In some embodiments, the body is at least partially hollow. Body  2701  comprises an exterior surface  2703 , a strikeface  2712 , a heel region  2702 , a toe region  2704  opposite heel region  2702 , a sole  2706 , and a rear  2710 . 
     Body  2701  of  FIGS.  13 - 17    further comprises a blade length. The blade length for body  2701  can be measured similar to blade length  3725  as shown and described in  FIG.  43    (i.e., a measurement parallel to the flat surface of the strikeface  3712 , from a toe edge  3726  of the strikeface  3712 , to strikeface end  3727  right before the strikeface  3712  integrally curves into the hosel). The blade length of the body  2701  can range from 2.80 inch (7.11 cm) to 3.00 inch (7.62 cm). For example, in some embodiments, the body  2701  can comprise a blade length of 2.80 inch (7.11 cm), 2.82 inch (7.16 cm), 2.84 inch (7.21 cm), 2.86 inch (7.26 cm), 2.88 inch (7.32 cm), 2.90 inch (7.37 cm), 2.93 inch (7.44 cm), 2.94 inch (7.47 cm), 2.96 inch (7.52 cm), 2.98 inch (7.57 cm), or 3.00 inch (7.62 cm). 
     The body  2701  further comprises a uniform thinned region transitioning from the bottom of the strikeface  2712  to the sole  2706 , toward a cascading sole portion of the sole (as described in greater detail below). In the illustrated embodiment, the uniform thinned region comprises a sole thickness measured perpendicular from the exterior surface  2703  to the interior surface at the uniform thinned region, which can remain constant from the bottom of the strikeface  2712  to adjacent the cascading sole portion of the sole. In some embodiments, the sole thickness of the uniform thinned region can be thinner than a conventional sole. For example, in some embodiments, the sole thickness of the uniform thinned region may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness of the uniform thinned region may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness of the uniformed thinned region can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
       FIG.  15    illustrates a cross-section of golf club head  2700  along the cross-sectional line XXIX-XXIX in  FIG.  13   , according to one embodiment. As seen in  FIG.  15   , strikeface  2712  comprises a high region  2976 , a middle region  2974 , and a low region  2972 . Rear  2710  comprises an upper region  2711  and a lower region  2713  ( FIG.  15   ). Upper region  2711  comprises a top rail  2715 , a rear wall  2923 , and a top wall  2719 . The top rail  2715  can be similar to the top rail  1015  of golf club head  1000 . In many embodiments, rear wall  2923  of rear  2710  is located below and adjacent to top rail  2715 , and a top wall  2719  of rear  2710  is located below and adjacent to rear wall  2923 . Lower region  2713  comprises a back wall  2921 , and a lower exterior wall  2927 , wherein back wall  2921  is located below an adjacent the top wall  2719 , and the lower exterior wall  2927  is located below and adjacent the back wall  2921 . Cavity  2730  is located on the exterior surface  2703 , below the top rail  2715  and rear wall  2923 , above the lower region  2713  of rear  2710 , and is defined by at least in part by upper region  2711  and lower region  2713 . 
     In some embodiments, top rail  2715  of the upper region  2711  of the rear  2710  can be a flatter and taller top rail or skirt than in the in irons known to one skilled in the art. The flatter and taller top rail can compensate for mis-hits on strikeface  2712  to increase playability off the tee. In some embodiments, the length of top rail  2715 , measured from heel region  2702  to toe region  2704 , can be 70% to 95% of the length of golf club head  2700 . In many embodiments, cavity  2730  comprises a top rail box spring design. In many embodiments, top rail  2715  and cavity  2730  provide an increase in the overall bending of strikeface  2712 . In some embodiments, the bending of strikeface  2712  can allow for a 2% to 5% increase of energy. Cavity  2730  allows for strikeface  2712  to be thinner and allow additional overall bending. For some fairway wood-type golf club head embodiments, cavity  2730  can be a reverse scoop or indentation of rear  2710  with body  2701  comprising a greater thickness or width toward sole  2706 . 
     In some embodiments, a height  2980  of rear wall  2923  of the upper region  2711  of rear  2710  can range from 0.125 inch (0.318 cm) to 0.75 inch (1.91 cm), or 0.150 inch (0.381 cm) to 0.400 inch (1.02 cm). For example, in some embodiments, the height  2980  of rear wall  2923  of the upper region  2711  of rear  2710  can be 0.175 inch (0.445 cm), 0.275 inch (0.699 cm), 0.375 inch (0.953 cm), 0.475 inch (1.21 cm), 0.575 inch (1.46 cm), or 0.675 inch (1.71 cm). In some embodiments, the height  2980  of rear wall  2923  of the upper region  2711  of rear  2710  can range from 0.150 inch (0.381 cm) to 0.200 inch (0.508 cm). In some embodiments, the height  2980  of rear wall  2923  of the upper region  2711  of rear  2710  can be 0.170 inch (0.432 cm). In some embodiments, the height  2980  of rear wall  2923  of the upper region  2711  of rear  2710  can be 5% to 25% of the height of golf club head  2700 . 
     The height  2980  of rear wall  2923  of the upper region  2711  of rear  2710 , as described herein, allows cavity  2730  to absorb at least a portion of the stress on strikeface  2712  during impact with a golf ball. A golf club head having a rear wall height greater than rear wall height  2980  described herein would absorb less stress (and allow less strikeface deflection) on impact than golf club head  2700  described herein, due to increased dispersion of the impact stress along the top rail prior to reaching the cavity. 
     In some embodiments, cavity  2730  is located above a lower region  2713  of rear  2710  and is defined at least in part by upper region  2711  and lower region  2713  of rear  2710 . Cavity  2730  comprises top wall  2719 , and a back wall  2921 . A first reference point  2922  is located between the top rail  2715  and rear wall  2923 . A second reference point  2982  is located between rear wall  2923  and top wall  2719 . A first inflection point  2986  is located between top wall  2719  of cavity  2730  and back wall  2921 . A third reference point  2924  is a point located on top wall  2719  closest to the strikeface  2712 . First reference point  2922  and second reference point  2982  create a first reference line  2929 . Second reference point  2982  and third reference point  2924  create a second reference line  2925 . Third reference point  2924  and first inflection point  2986  create a third reference line  2926 . 
     Golf club head  2700  further comprises a height  2988  of top wall  2719 , measured parallel to strikeface  2712  and from the second reference point  2982  to first inflection point  2986 . In many embodiments, height  2988  can range from 0.100 inch (0.254 cm) to 0.600 inch (1.524 cm). For example, height  2988  can be 0.100 inch (0.254 cm), 0.150 inch (0.381 cm), 0.200 inch (0.508 cm), 0.250 inch (0.635 cm), 0.300 inch (0.762 cm), 0.350 inch (0.889 cm), 0.400 inch (1.016 cm), 0.450 inch (1.143 cm), 0.500 inch (1.27 cm), 0.550 inch (1.397 cm), or 0.600 inch (1.524 cm). In many embodiments, height  2988  can range from 0.500 inch (1.27 cm) to 0.600 inch (1.524 cm). In some embodiments, height  2488  of top wall  2719  can be 0.500 inch (1.27 cm), 0.510 inch (1.295 cm), 0.520 inch (1.321 cm), 0.530 inch (1.346 cm), 0.540 inch (1.372 cm), 0.550 inch (1.397 cm), 0.560 inch (1.422 cm), 0.570 inch (1.448 cm), 0.580 inch (1.473 cm), 0.590 inch (1.499 cm), or 0.600 inch (1.524 cm). 
     In many embodiments, second reference point  2982  can be 0.125 inch (0.318 cm) to 1.25 inches (3.18 cm) or 0.25 inch (0.635 cm) to 1.25 inches (3.18 cm) to apex  2928  of top rail  2715 . For example, the second reference point  2982  can be 0.125 inch (0.318 cm), 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch (1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), or 1.25 inches (3.18 cm) below the apex  2928  of top rail  2715 . 
     In many embodiments, top wall  2719  of cavity  2730  can be substantially parallel to strikeface  2712 . In other embodiments, top wall  2719  is not substantially parallel to strikeface  2712 . In some embodiments, top wall  2719  of cavity  2730  is substantially parallel to rear wall  2923  of upper region  2711  of rear  2710 . In a number of embodiments, a portion of top wall  2719  extends away from rear wall  2923  toward strikeface  2712  from second reference point  2982  to third reference point  2924 . In some embodiments, the portion of top wall  2719  extending away from rear wall  2923  toward strikeface  2712  from second reference point  2982  to third reference point  2924  can be straight, curved upward, or curved downward. In many embodiments, a portion of top wall  2719  of cavity  2730  is angled away from strikeface  2712  from third reference point  2924  to first inflection point  2986 . In some embodiments, the portion of top wall  2719  angled away from strikeface  2712  from third reference point  2924  to first inflection point  2986  can be straight, curved upward, or curved downward. This orientation of top wall  2719  creates a buckling point, hinge point or plastic hinge to direct the stress of impact toward cavity  2730  and to allow increased flexing of strikeface  2712  during impact. 
     Lower region  2713  of rear  2710  comprises back wall  2921  of cavity  2730  and the lower exterior wall  2927 . In some embodiments, back wall  2921  of cavity  2730  can have a back wall length  2990  measured from first inflection point  2986  to a second inflection point  2992  located between the back wall  2921 , and the lower exterior wall  2927 . In a number of embodiments, back wall length  2990  can range from 0.150 inch (0.381 cm) to 0.400 inch (1.02 cm). In many embodiments, back wall length  2990  can be 0.150 inch (0.381 cm), 0.160 inch (0.406 cm), 0.170 inch (0.432 cm), 0.180 inch (0.457 cm), 0.190 inch (0.483 cm), 0.200 inch (0.508 cm), 0.210 inch (0.533 cm), 0.220 inch (0.559 cm), 0.230 inch (0.584 cm), 0.240 inch (0.61 cm), 0.250 inch (0.635 cm), 0.260 inch (0.660 cm), 0.270 inch (0.686 cm), 0.280 inch (0.711 cm), 0.290 inch (0.737 cm), 0.300 inch (0.762 cm), 0.310 inch (0.787 cm), 0.320 inch (0.813 cm), 0.330 inch (0.838 cm), 0.340 inch (0.864 cm), 0.350 inch (0.889 cm), 0.360 inch (0.914 cm), 0.370 inch (0.94 cm), 0.380 inch (0.965 cm), 0.390 inch (0.991 cm), or 0.400 inch (1.02 cm). 
     In some embodiments, a lower angle  2951  can be measured from between the back wall  2921  and the lower exterior wall  2927 . In some embodiments, lower angle  2951  can be less than 180 degrees. In a number of embodiments, lower angle  2951  can range from 30 degrees to 180 degrees. In various embodiments, lower angle  2951  can range from70 degrees to 130 degrees. In some embodiments, lower angle  2951  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, or 130 degrees. 
     In some embodiments, an inflection angle  2996  measured from third reference line  2926  to back wall  2921  can range from 70 degrees to 150 degrees. In some embodiments, inflection angle  2996  can range from 90 degrees to 130 degrees. In some embodiments, inflection angle  2996  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, or 150 degrees. In many embodiments, inflection angle  2996  allows first inflection point  2986  to act as a buckling point or plastic hinge upon golf club head  2700  impacting the golf ball at strike face  2712 . In some embodiments, the wall thickness at the first inflection point  2986  can be thinner than at the top wall  2719  and back wall  2921 . 
     In many embodiments, first inflection point  2986 , adjacent to back wall  2921 , can range from 0.25 inch (0.635 cm) to 2.0 inches (5.08 cm), or 0.5 inch (1.27 cm) to 1.5 inches (3.81 cm) below the apex  2928  of top rail  2715 . For example, the first inflection point  2986  can be 0.25 inch (0.635 cm), 0.5 inch (1.27 cm), 0.75 inch (1.91 cm), 1.0 inch (2.53 cm), 1.25 inches (3.18 cm), 1.5 inches (3.81 cm), 1.75 inches (4.45 cm) or 2.0 inches (5.08 cm) below the apex  2928  of top rail  2715 . In some embodiments, the maximum height of the back wall  2921 , measured perpendicular to a ground plane  2903  when golf club head  2700  is at address from a lowest point of sole  2706  to first inflection point  2986 , can range from 0.25 inch (0.635 cm) to 3 inches (7.62 cm), or 0.50 inch (1.27 cm) to 2 inches (5.08 cm). For example, the first inflection point  2986  can be 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch (1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), 1.25 inches (3.18 cm), 1.375 inches (3.49 cm), 1.5 inches (3.81 cm), 1.625 inches (4.12 cm), 1.75 inches (4.45 cm), 1.875 inches (4.76 cm), 2.0 inches (5.08 cm), 2.125 inches (5.40 cm), 2.25 inches (5.71 cm), 2.375 inches (6.03 cm), 2.5 inches (6.35 cm), 2.625 inches (6.67 cm), 2.75 inches (7.00 cm), 2.875 inches (7.30 cm), or 3.0 inches (7.62 cm) above a lowest point of sole  2706  perpendicular to the ground plane  2903  when golf club head  2700  is at address. 
     In some embodiments, a back wall angle  2905  measured from back wall  2921  to ground plane  2903  can range from 15 degrees to 45 degrees. In some embodiments, back wall angle  2905  can be 15 degrees, 16 degrees, 17 degrees, 18 degrees, 19 degrees, 20 degrees, 21 degrees, 22 degrees, 23 degrees, 24 degrees, 25 degrees, 26 degrees, 27 degrees, 28 degrees, 29 degrees 30 degrees, 31 degrees, 32 degrees, 33 degrees, 34 degrees, 35 degrees, 36 degrees, 37 degrees, 38 degrees, 39 degrees, 40 degrees, 41 degrees, 42 degrees, 43 degrees, 44 degrees, or 45 degrees. 
     In some embodiments, cavity  2730  can further comprise at least one channel  2739  ( FIG.  13   ). In many embodiments, channel  2739  extends from heel region  2702  ( FIG.  13   ) to toe region  2704  ( FIG.  13   ). Channel  2739  comprises a channel width measured from second reference point  2982  to top wall  2719  substantially parallel to ground plane  2903 , where channel width can vary in a direction from top rail  2715  to sole  2706 . In some embodiments, a maximum channel width  2932 , measured from first inflection point  2986  to second reference point  2982  substantially parallel to ground plane  2903 , can be substantially constant throughout channel  2739  from heel region  2702  to toe region  2704 . In some embodiments, maximum channel width  2932  ( FIG.  15   ) can range from 0.008 inch (0.2 mm) to 1 inch (25 mm), or 0.008 inch (0.2 mm) to 0.31 inch (8 mm). For example, maximum channel width  2932  can be 0.008 inch (0.2 mm), 0.016 inch (0.4 mm), 0.024 inch (0.6 mm), 0.031 inch (0.8 mm), 0.039 inch (1.0 mm), 0.079 inch (2 mm), 0.12 inch (3 mm), 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.39 inch (10 mm), 0.59 inch (15 mm), 0.79 inch (20 mm), or 0.98 inch (25 mm). In other embodiments, a channel toe region width of channel  2739  is less than a channel heel region width of channel  2739 . In other embodiments, the channel heel region width is less than the channel toe region width. In other embodiments, a channel middle region width of channel  2739  can be less than at least one of the channel heel region width or the channel toe region width. In other embodiments, the channel middle region width can be greater than at least one of the channel heel region width or the channel toe region width. In some embodiments, channel  2739  is symmetrical from heel to toe. In other embodiments, channel  2739  is non-symmetrical. In other embodiments, channel  2739  can further comprise at least two partial channels. In some embodiments, channel  2739  can comprise a series of partial channels interrupted by one or more bridges. In some embodiments, the one or more bridges can be approximately the same thickness as the thickness of top rail  2715 . 
     Maximum channel width  2932 , as described herein, allows absorption of stress from strikeface  2712  on impact. A golf club head having a channel width less than the maximum channel width described herein (e.g. a golf club head with a less pronounced cavity) would allow less stress absorption from the strikeface on impact (due to less material on the upper region  2711  of rear  2710 ), and therefore would experience less strikeface deflection than golf club head  2700  described herein. 
     In many embodiments, cavity  2730  further comprises a back cavity angle  2935 . Back cavity angle  2935  is measured from first reference line  2929  to second reference line  2925 . In many embodiments, back cavity angle  2935  can range from 15 degrees to 80 degrees. In some embodiments, back cavity angle  2935  is 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees or 80 degrees. 
       FIG.  16    illustrates a view of top rail  2715  and a portion of rear  2710  of the cross-section of golf club head  2700  of  FIG.  13    different from cross-section of golf club head  1200  as shown in  FIG.  4   . In many embodiments, golf club head  2700  comprises a rear angle  3040 , a top rail angle  3045 , and a strikeface angle  3050 . Rear angle  3040  is measured from second reference line  2925  to rear wall  2923  of upper region  2711 . In many embodiments, rear angle  3040  can range from 70 degrees to 140 degrees. In some embodiments, rear angle  3040  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, or 140 degrees. Top rail angle  3045  is measured from rear wall  2923  of upper region  2711  to top rail  2715 . In many embodiments, top rail angle  3045  can range from 35 degrees to 120 degrees or 70 degrees to 110 degrees. In some embodiments, top rail angle  3045  can be 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, or 120 degrees. Strikeface angle  3050  is measured from strikeface  2712  to top rail  2715 . In many embodiments, strikeface angle  3050  can range from 70 degrees to 160 degrees or 70 degrees to 110 degrees. In some embodiments, strikeface angle  3050  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, or 160 degrees. 
     Upper region  2711  further comprises a minimum gap  3090  measured from third reference point  2924  of an inner surface  2919  of top wall  2719  to an inner surface  2919  of strikeface  2712 , perpendicular to strikeface  2712 . In some embodiments, minimum gap  3090  can range from 0.079 inch (2 mm) to 0.39 inch (10 mm). For example, the minimum gap  3090  can be 0.079 inch (2 mm), 0.16 inch (4 mm), 0.24 inch (6 mm), 0.31 inch (8 mm), or 0.39 inch (10 mm). In other embodiments, the minimum gap  3090  can range from 0.16 inch (4 mm) to 0.55 inch (14 mm). In some embodiments, the minimum gap  3090  can be 0.55 inch (14 mm), 0.47 inch (12 mm), 0.39 inch (10 mm), 0.31 inch (8 mm), 0.24 inch (6 mm), or 0.16 inch (4 mm). 
       FIG.  17    illustrates a simplified cross-sectional view of golf club head  2700 , similar to the detailed cross-section of golf club head  2700  illustrated in  FIG.  15   . Golf club head  2700  includes cavity  2730 , upper region  2711 , lower region  2713 , and exterior surface  2703 . In many embodiments, a maximum upper distance  3192  measured as the perpendicular distance from exterior surface  2703  of strikeface  2712  to exterior surface  2703  of second reference point  2982  of upper region  2711  can range from 0.20 inch to 0.59 inch (5 mm to 15 mm). For example, maximum upper distance  3192  can be 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (8.89 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), 0.47 inch (12 mm), 0.51 inch (13 mm), 0.55 inch (14 mm), or 0.59 inch (15 mm). In some embodiments, maximum upper distance  3192  can be 0.358 inch (9.09 mm). Further, a minimum upper distance  3194  measured as the perpendicular distance from exterior surface  2703  of strikeface  2712  to exterior surface  2703  of third inflection point  2924  can range from 0.09 inch to 0.47 inch (2.28 mm to 12 mm). For example, minimum upper distance  3194  can be 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (9 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), or 0.47 inch (12 mm). In some embodiments, minimum upper distance  3194  can be 0.309 inch (7.85 mm). Further still, a maximum lower distance  3196  measured as the perpendicular distance from exterior surface  2703  of strikeface  2712  to exterior surface  2703  of a fourth reference point  2920  located between the lower exterior wall  2927  and the sole  2706  can range from 0.98 inch to 1.57 inch (25 mm to 40 mm). For example, maximum lower distance  3196  can be 0.98 inch (25 mm), 1.02 inch (26 mm), 1.06 inch (27 mm), 1.10 inch (28 mm), 1.14 inch (29 mm), 1.18 inch (30 mm), 1.22 inch (31 mm), 1.26 inch (32 mm), 1.30 inch (33 mm), 1.34 inch (34 mm), 1.38 inch (35 mm), 1.42 inch (36 mm), 1.46 inch (37 mm), 1.50 inch (38 mm), 1.54 inch (39 mm), 1.57 inch or (40 mm). In some embodiments, maximum lower distance  3196  can be 1.302 inch (33.1 mm). In many embodiments, maximum lower distance  3196  is greater than maximum upper distance  3192 , and maximum upper distance  3192  is greater than minimum upper distance  3194 . 
     In many embodiments, cavity  2730  can provide an increase in golf ball speed over golf club head  1200  ( FIG.  16   ) or other standard golf club heads, can reduce the spin rate of standard hybrids club heads, and can increase the launch angle over both the standard hybrid and iron club heads. In many embodiments, the shape of cavity  2730  determines the level of spring and timing of the response of golf club head  2700 . When the golf ball impacts strikeface  2712  of club head  2700  with cavity  2730 , strikeface  2712  springs back like a drum, and rear  2710  bends in a controlled buckle manner. In many embodiments, top rail  2715  can absorb more stress over greater volumetric space than a top rail in a golf club head without cavity  2730 . The length, depth and width of cavity  2730  can vary. These parameters provide control regarding how much spring back is present in the overall design of club head  2700 . 
     Upon impact with the golf ball, strikeface  2712  can bend inward at a greater distance than on a golf club without cavity  2730 . In some embodiments, strikeface  2712  has a 10% to a 50% greater deflection than a strikeface on a golf club head without cavity  2730 . In some embodiments, strikeface  2712  has a 5% to a 40% or a 10% to a 20% greater deflection than a strikeface on a golf club head without cavity  2730 . For example, strikeface  2712  can have a 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40% greater deflection than a strikeface on a golf club head without cavity  2730 . In many embodiments, there is both a greater distance of retraction by strikeface  2712  due to the hinge and bending of cavity  2730  over a standard strikeface that does not have a back portion of the club without the cavity. 
     In many embodiments, the face deflection is greater with club head  2700  having cavity  2730 , as a greater buckling occurs at first inflection angle  2986  of top wall  2719  upon impact with a golf ball. Cavity  2730 , however, provides a greater dispersion of stress along top rail  2715 , rear wall  2923 , and top wall  2719 , and the spring back force is transferred from cavity  2730  and first inflection point  2986  of top wall  2719  to strikeface  2712 . A standard top rail, rear wall and top wall without a cavity does not have this hinge/buckling effect, nor does it absorb a high level of stress over a large volumetric area of the top rail, rear wall and top wall. Therefore, the standard strikeface does not contract and then recoil as much as strikeface  2712 . Further, both a larger region of strikeface  2712 , top rail  2715 , rear wall  2923 , and top wall  2719  absorb more stress than the same crown region of a standard golf club head with a standard top rail, top wall and no cavity. In many embodiments, although there is greater stress along a greater area above cavity  2730  than the same area in a standard club without the cavity, the durability of the club head with and without the cavity is the same. By adding more spring to the back end of the club (due to the inward inclination of a portion of top wall  2719  toward strikeface  2712 ), more force is displaced throughout the volume of the structure. The stress is observed over a greater area of strikeface  2712 , top rail  2715 , rear wall  2923 , and top wall  2719  of golf club head  2700 . Peak stresses can be seen in the standard top rail club head. However, more peak stresses are seen in golf club head  2700  but distributed over a large volume of the material. The hinge and bend regions of golf club head  2700  (i.e., the region above cavity  2730  and cavity  2730  itself) will not deform as long as the stress does not meet the critical buckling threshold. Cavity  2730  and its placement can be designed to be under the critical K value of the buckling threshold. 
     As shown in  FIG.  17   , a further deflection feature of the golf club head  2700  can be the uniform thinned region  3160 , located at the sole  2706  and stretching between the rear  2710  of the body  2701  and the strikeface  2712 , toward a cascading sole portion of the sole (as described in greater detail below). The uniform thinned region  3160  can provide multiple benefits. First, the uniform thinned region  3160  can reduce stress on the strikeface  2712  caused during impact with the golf ball. Second, the uniform thinned region  3160  can bend allowing the strikeface  2712  to experience greater deflection. Third, the uniform thinned region  3160  removes weight from the sole area, allowing the weight to be redistributed more toward the rear of the golf club head  2700 . At impact, the energy imparted to the strikeface  2712  by the golf ball can cause the uniform thinned region  3160  to bend outward, which in turn increases the strikeface  2712  deflection. After bending, the uniform thinned region  3160  rebounds back to its original position returning the majority of the energy from impact back to the golf ball. The result is the golf club head  2700  imparts increased ball speeds and greater travel distances to the golf ball after impact. 
     In some embodiments, body  2701  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, body  2701  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, strikeface  2712  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, strikeface  2712  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, body  2701  can comprise the same material as strikeface  2712 . In some embodiments, body  2701  can comprise a different material than strikeface  2712 . 
       FIG.  18    illustrates a back perspective view of an embodiment of golf club head  3200 , and  FIG.  19    illustrates a back heel-side perspective view of golf club head  3200  according to the embodiment of  FIG.  18   . In some embodiments, golf club head  3200  can be similar to golf club head  1000  ( FIG.  1   ), golf club head  2200  ( FIG.  8   ), and/or golf club head  2700  ( FIG.  13   ). Golf club head  3200  can be an iron-type golf club head. In other embodiments, golf club head  3200  can be a hybrid-type, or a fairway wood-type golf club head. In some embodiments, golf club head  3200  does not comprise a badge or a custom tuning port. 
     Golf club head  3200  comprises a body  3201 . In some embodiments, body  3201  can be similar to body  1001  ( FIG.  1   ), body  2201  ( FIG.  8   ), and/or body  2701  ( FIG.  13   ). In some embodiments, the body  3201  is hollow. In other embodiments, the body is at least partially hollow. Body  3201  comprises an exterior surface  3203 , a strikeface  3212 , a heel region  3202 , a toe region  3204  opposite the heel region  3202 , a sole  3206 , a top rail  3215 , and a rear  3210 . 
     Body  3201  of  FIGS.  18 - 22    further comprises a blade length. The blade length for body  3201  can be measured similar to blade length  3725  as shown and described in  FIG.  29    (i.e., a measurement parallel to the flat surface of the strikeface  3712 , from a toe edge  3726  of the strikeface  3712 , to strikeface end  3727  right before the strikeface  3712  integrally curves into the hosel). The blade length of the body  3201  can range from 2.70 inch (6.86 cm) to 3.00 inch (7.62 cm). For example, in some embodiments, the body  3201  can comprise a blade length of 2.74 inch (6.96 cm), 2.78 inch (7.06 cm), 2.82 inch (7.16 cm), 2.86 inch (7.26 cm), 2.90 inch (7.37 cm), 2.94 inch (7.47 cm), 2.98 inch (7.57 cm), or 3.00 inch (7.62 cm). 
     The body  3201  further comprises a uniform thinned region transitioning from the bottom of the strikeface  3212  to the sole  3206 , toward a cascading sole portion of the sole (as described in greater detail below). In the illustrated embodiment, the uniform thinned region comprises a sole thickness measured perpendicular from the exterior surface  3203  to the interior surface at the uniform thinned region, which can remain constant from the bottom of the strikeface  3212  to adjacent the cascading sole portion of the sole. In some embodiments, the sole thickness of the uniform thinned region can be thinner than a conventional sole. For example, in some embodiments, the sole thickness of the uniform thinned region may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness of the uniform thinned region may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness of the uniformed thinned region can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
       FIG.  20    illustrates a cross-section of golf club head  3200  along the cross-sectional line XXXIV-XXXIV in  FIG.  18   , according to one embodiment. As seen in  FIG.  18   , strikeface  3212  comprises a high region  3476 , a middle region  3474 , and a low region  3472 . Rear  3210  can comprise an upper region  3211 , a lower region  3213 , and a cavity  3230 . Upper region  3211  comprises top rail  3215 , a rear wall  3423 , and a top wall  3219 . In many embodiments, the rear wall  3423  of rear  3210  is located below and adjacent to the top rail  3215 , and the top wall  3219  of rear  3210  is located below and adjacent to rear wall  3423 . Lower region  3213  comprises a back wall  3421 , and a lower exterior wall  3427 . Cavity  3230  is located on the exterior surface  3203 , below the top rail  3215  and rear wall  3423 , above the lower exterior wall  3427  of rear  3210 , and is defined by at least in part by upper region  3211  and lower region  3213 . 
     In some embodiments, top rail  3215  of the upper region  3211  can be a flatter and taller top rail or skirt than in irons known to one skilled in the art. The flatter and taller rail  3215  can compensate for mis-hits on strikeface  3212  to increase playability off the tee. In some embodiments, the length of top rail  3215 , measured from heel region  3202  to toe region  3204 , can be 70% to 95% of the length of golf club head  3200 . In many embodiments, cavity  3230  comprises a top rail box spring design. In many embodiments, top rail  3215  and cavity  3230  provide an increase in the overall bending of strikeface  3212 . In some embodiments, the bending of strikeface  3212  can allow for a 2% to 5% increase of energy. Cavity  3230  allows for strikeface  3212  to be thinner and allow additional overall bending. For some fairway iron-type golf club head embodiments, cavity  3230  can be a reverse scoop or indentation of rear  3210  with body  3201  comprising a greater thickness toward sole  3206 . 
     In some embodiments, a height  3480  of rear wall  3423  of upper region  3211  of rear  3210  can range from 0.115 inch (0.292 cm) to 0.25 inch (0.635 cm), or 0.130 inch (0.330 cm) to 0.20 inch (0.508 cm). For example, in some embodiments, the height  3480  of rear wall  3423  of the upper region  3211  of rear  3210  can be 0.115 inch (0.292 cm), 0.125 inch (0.318 cm), 0.135 inch (0.343 cm), 0.145 inch (0.368 cm), 0.155 inch (0.394 cm), 0.165 inch (0.419 cm), 0.175 inch (0.445 cm), 0.185 inch (0.470 cm),  0 . 195  (0.495 cm), or 0.250 inch (0.635 cm). In some embodiments, the height  3480  of rear wall  3423  of the upper region  3211  of rear  3210  can range from 0.150 inch (0.381 cm) to 0.210 inch (0.533 cm). In some embodiments, the height  3480  of rear wall  3423  of the upper region  3211  of rear  3210  can be 0.166 inch (0.422 cm). In some embodiments, the height  3480  of rear wall  3423  of upper region  3211  of rear  3210  can range from 3% to 15% of the height of the golf club head  3200 . 
     The height  3480  of rear wall  3423  of the upper region  3211  of rear  3210 , as described herein, allows cavity  3230  to absorb at least a portion of the stress on strikeface  3212  during impact with a golf ball. A golf club head having a rear wall height greater than rear wall height  3480  described herein would absorb less stress (and allow less strikeface deflection) in impact than golf club head  3200  described herein, due to increased dispersion of the impact stress along the top rail prior to reaching the cavity. 
     In some embodiments, cavity  3230  is located above a lower region  3213  of rear  3210  and is defined at least in part by upper region  3211  and lower region  3213  of rear  3210 . Cavity  3230  comprises top wall  3219 , and back wall  3421 . A first reference point  3422  is located between the top rail  3215  and rear wall  3423 . A second reference point  3482  is located between rear wall  3423  and top wall  3219 . A first inflection point  3486  is located between top wall  3219  of cavity  3230  and back wall  3421 . A third reference point  3424  is point located on top wall  3219  closest to the strikeface  3212 . First reference point  3422  and second reference point  3482  create a first reference line  3429 . Second reference point  3482  and third reference point  3424  create a second reference line  3425 . Third reference point  3424  and first inflection point  3486  create a third reference line  3426 . 
     Golf club head  3200  further comprises a height  3488  of top wall  3219 , measured parallel to strikeface  3212  and from the second reference point  3482  to first inflection point  3486 . In many embodiments, height  3488  can range from 0.100 inch (0.254 cm) to 0.700 inch (1.778 cm). For example, height  3488  can be 0.100 inch (0.254 cm), 0.150 inch (0.381 cm), 0.200 inch (0.508 cm), 0.250 inch (0.635 cm), 0.300 inch (0.762 cm), 0.350 inch (0.899 cm), 0.400 inch (1.016 cm), 0.450 inch (1.143 cm), 0.500 inch (1.270 cm), 0.550 inch (1.397 cm), 0.600 inch (1.524 cm), 0.650 inch (1.651 cm), or 0.700 inch (1.778 cm). In many embodiments, height  3488  can range from 0.300 inch (0.762 cm) to 0.550 inch (1.397 cm). In some embodiments, height  3488  of top wall  3219  can be 0.300 inch (0.762 cm), 0.330 inch (0.838 cm), 0.360 inch (0.914 cm), 0.390 inch (0.991 cm), 0.420 inch (1.067 cm), 0.450 inch (1.143 cm), 0.480 inch (1.219 cm), 0.510 inch (1.295 cm), or 0.540 inch (1.312 cm). 
     In many embodiments, second reference point  3482  can range from 0.075 inch (0.191 cm) to 1.00 inches (2.54 cm) or 0.150 inch (0.381 cm) to 0.180 inches (0.457 cm) to apex  3428  of top rail  3215 . For example, the second reference point  3482  can be 0.075 inch (0.191 cm), 0.095 inch (0.241 cm), 0.115 inch (0.292 cm), 0.135 inch (0.343 cm), 0.155 inch (0.394 cm), 0.175 inch (0.445 cm), 0.190 inch (0.483 cm), or 1.000 inch (2.54 cm) below the apex  3428  of top rail  3215 . 
     In many embodiments, top wall  3219  of cavity  3230  can be substantially parallel to strikeface  3212 . In other embodiments, top wall  3219  is not substantially parallel to strikeface  3212 . In some embodiments, top wall  3219  of cavity  3230  is substantially parallel to rear wall  3423  of upper region  3211  of rear  3210 . In a number of embodiments, a portion of top wall  3219  extends away from top rail  3215  toward strikeface  3212  from second reference point  3482  to third reference point  3424 . In some embodiments, the portion of top wall  3219  extending away from top rail  3215  toward strikeface  3212  from second reference point  3482  to third reference point  3424  can be straight, curved upward, or curved downward. In many embodiments, a portion of top wall  3219  of cavity  3230  is angled away from strikeface  3212  from third reference point  3424  to first inflection point  3486 . In some embodiments, the portion of top wall  3219  angled away from strikeface  3212  from third reference point  3424  to first inflection point  3486  can be straight, curved upward, or curved downward. This orientation of top wall  3219  creates a buckling point, hinge point or plastic hinge to direct the stress of impact toward cavity  3230  and to allow increased flexing of strikeface  3212  during impact. 
     Lower region  3213  of rear  3210  comprises back wall  3421  of cavity  3230  and lower exterior wall  3427 . In some embodiments, back wall  3421  of cavity  3230  can have a back wall length  3490  measured from first inflection point  3486  to a second inflection point  3492  located between the back wall  3421  and the lower exterior wall  3427 . In a number of embodiments, back wall length  3490  can range from 0.100 inch (0.254 cm) to 0.350 inch (0.889 cm). In many embodiments, back wall length  3490  can be 0.100 inch (0.254 cm), 0.125 inch (0.318 cm), 0.150 inch (0.381 cm), 0.175 inch (0.445 cm), 0.200 inch (0.508 cm), 0,225 inch (0.572 cm), 0,250 inch (0.635 cm), 0,275 inch (0.699 cm), 0,300 inch (0.762 cm), 0,325 inch (0.826 cm), or 0,350 inch (0.889 cm). 
     In some embodiments, a lower angle  3451  can be measured from between the back wall  3421  and the lower exterior wall  3427 . In some embodiments, lower angle  3451  can be less than 180 degrees. In a number of embodiments, lower angle  3451  can range from 30 degrees to 180 degrees. In various embodiments, lower angle  3451  can range from 70 degrees to 130 degrees. In some embodiments, lower angle  3451  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, or 130 degrees. 
     In some embodiments, an inflection angle  3496  measured from third reference line  3426  to back wall  3421  can range from 70 degrees to 150 degrees. In some embodiments, inflection angle  3496  can range from 90 degrees to 130 degrees. In some embodiments, inflection angle  3496  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, or 150 degrees. In many embodiments, inflection angle  3496  allows first inflection point  3486  to act as a buckling point or plastic hinge upon golf club head  3200  impacting the golf ball at strikeface  3212 . In some embodiments, the wall thickness at the first inflection point  3486  can be thinner than at the top wall  3219  and back wall  3421 . 
     In many embodiments, first inflection point  3486 , adjacent to back wall  3421  can range from 0.20 inch (0.508 cm) to 1.0 inch (2.54 cm), or 0.5 inch (1.27 cm) to 0.7 inch (1.778 cm) below the apex  3428  of top rail  3215 . For example, the first inflection point  3486  can be 0.20 inch (0.508 cm), 0.25 inch (0.635 cm), 0.30 inch (0.762 cm), 0.35 inch (0.889 cm), 0.40 inch (1.016 cm), 0.45 inch (1.143 cm), 0.50 inch (1.27 cm), 0.55 inch (1.397 cm), 0.60 inch (1.524 cm), 0.65 inch (1.651 cm), 0.70 inch (1.778 cm), 0.75 inch (1.905 cm), 0.80 inch (2.032 cm), 0.85 inch (2.159 cm), 0.90 inch (2.286 cm), 0.95 inch (2.413 cm), or 1.0 inch (2.54 cm) below the apex  3428  of top rail  3215 . In some embodiments, the maximum height of the back wall  3421 , measured perpendicular to a ground  3403  when golf club head  3200  is at address, from a lowest point of sole  3206  to first inflection point  3486 , can range from 0.25 inch (0.635 cm) to 3 inches (7.62 cm), or 0.50 inch (1.27 cm) to 2 inches (5.08 cm). For example, the first inflection point  3486  can be 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch 1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), 1.25 inches (3.18 cm), 1.375 inches (3.49 cm), 1.5 inches (3.81 cm), 1,625 inches (4.12 cm), 1.75 inches (4.45 cm), 1.875 inches (4.76 cm), 2.0 inches (5.08 cm), 2.125 inches (5.40 cm), 2.25 inches (5.71 cm), 2.375 inches (6.03 cm), 2.5 inches (6.35 cm), 2.625 inches (6.67 cm), 2.75 inches (7.00 cm), 2.875 inches (7.30 cm) or 3.0 inches (7.62 cm) above a lowest point of sole  3206  to the ground  3403  when golf club head  3200  is at address. 
     In some embodiments, a back wall angle  3405  measured from back wall  3421  to ground plane  3403  can range from 15 degrees to 45 degrees. In some embodiments, back wall angle  3405  can be 15 degrees, 16 degrees, 17 degrees, 18 degrees, 19 degrees, 20 degrees, 21 degrees, 22 degrees, 23 degrees, 24 degrees, 25 degrees, 26 degrees, 27 degrees, 28 degrees, 29 degrees, 30 degrees, 31 degrees, 32 degrees, 33 degrees, 34 degrees, 35 degrees, 36 degrees, 37 degrees, 38 degrees, 39 degrees, 40 degrees, 41 degrees, 42 degrees, 43 degrees, 44 degrees, or 45 degrees. 
     In some embodiments as illustrated in  FIG.  18   , cavity  3230  can further comprise at least one channel  3239 . In many embodiments, channel  3239  extends from heel region  3202  to toe region  3204 . Channel  3239  comprises a channel width measured from second reference point  3482  to top wall  3219  substantially parallel to ground plane  3403 , where channel width can vary in a direction from top rail  3215  to sole  3206 . In some embodiments, a maximum channel width  3432 , measured from first inflection point  3486  to second reference point  3482  substantially parallel to ground plane  3403 , can be substantially constant throughout the channel  3230  from heel region  3202  to toe region  3204 . In some embodiments as illustrated in  FIG.  20   , maximum channel width  3432  can range from 0.039 inch (1 mm) to 0.590 inch (15 mm), or 0.150 inch (3.81 mm) to 0.400 inch (10.16 mm). For example, maximum channel width  3432  can be 0.039 inch (1.0 mm), 0.079 inch (2 mm), 0.12 inch (3 mm), 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.39 inch (10 mm), or 0.59 inch (15 mm). In other embodiments, a channel toe region width of channel  3239  is less than a channel heel region width of channel  3239 . In other embodiments, the channel heel region width is less than the channel toe region width. In other embodiments, a channel middle region width of channel  3239  can be less than at least one of the channel heel region width or the channel toe region width. In other embodiments, the channel middle region width can be greater than at least one of the channel heel region width or the channel toe region width. In some embodiments, channel  3239  is symmetrical from heel to toe. In other embodiments, channel  3239  is non-symmetrical. In other embodiments, channel  3239  can further comprise at least two partial channels. In some embodiments, channel  3239  can comprise a series of partial channels interrupted by one or more bridges. In some embodiments, the one or more bridges can be approximately the same thickness as the thickness of upper region  3211  of top rail  3215 . 
     Maximum channel width  3432 , as described herein, allows absorption of stress from strikeface  3212  on impact. A golf club head having a channel width less than the maximum channel width  3432  described here (e.g., a golf club head with a less pronounced cavity) would allow less stress absorption from the strikeface on impact (due to less material on the upper region  3211  of rear  3210 ), and therefore would experience less strikeface deflection than golf club head  3200  described herein. 
     In many embodiments, back cavity  3230  further comprises a cavity angle  3435 . Back cavity angle  3435  is measured from first reference line  3429  to second reference line  3425 . In many embodiments, back cavity angle  3435  can range from 15 degrees to 80 degrees. In some embodiments, back cavity angle  3435  can be 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, or 80 degrees. 
       FIG.  21    illustrates a view of top rail  3215  and a portion of rear  3210  of the cross-section of golf club head  3200  of  FIG.  18    different from cross-section of golf club head  1200  as shown in  FIG.  4   . In many embodiments, golf club head  3200  comprises a rear angle  3540 , a top rail angle  3545 , and a strikeface angle  3550 . Rear angle  3540  is measured from second reference line  3425  to rear wall  3423  of upper region  3211 . In many embodiments, rear angle  3540  can range from 70 degrees to 140 degrees. In some embodiments, rear angle  3540  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, or 140 degrees. Top rail angle  3545  is measured from rear wall  3423  of upper region  3211  to top rail  3215 . In many embodiments, top rail  3545  can range from 35 degrees to 120 degrees or 70 degrees to 110 degrees. In some embodiments, top rail angle  3545  can be 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, or 120 degrees. Strikeface angle  3550  is measured from strikeface  3212  to top rail  3215 . In many embodiments, strikeface angle  3550  can range from 70 degrees to 160 degrees or 70 degrees to 110 degrees. In some embodiments, strikeface angle  3550  can be 70 degrees, 75 degrees, 80 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, or 160 degrees. 
     Upper region  3211  further comprises a minimum gap  3590  measured from third reference point  3424  of an inner surface  3419  of top wall  3219  to an inner surface  3419  of strikeface  3212 , perpendicular to strikeface  3212 . In some embodiments, minimum gap  3590  can range from 0.079 inch (2 mm) to 0.24 inch (6 mm). For example, the minimum gap  3590  can be 0.079 inch (2 mm), 0.118 inch (3 mm), 0.16 inch (4 mm), 0.197 inch (5 mm) or 0.24 inch (6 mm). In other embodiments, the minimum gap  3590  can range from 0.118 inch (3 mm) to 0.16 inch (4 mm). In some embodiments, the minimum gap  3590  can be 0.135 inch (3.429 mm). 
       FIG.  22    illustrates a simplified cross-sectional view of golf club head  3200 , similar to the detailed cross-section of golf club head  3200  illustrated in  FIG.  20   . Golf club head  3200  include cavity  3230 , upper region  3211 , lower region  3213 , and exterior surface  3203 . In many embodiments, a maximum upper distance  3692  measured as the perpendicular distance from exterior surface  3203  of strikeface  3212  to exterior surface  3203  of second reference point  3482  of upper region  3211  can range from 0.20 inch to 0.59 inch (5 mm to 15 mm). For example, maximum upper distance  3692  can be 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (8.89 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), 0.47 inch (12 mm), 0.51 inch (13 mm), 0.55 inch (14 mm), or 0.59 inch (15 mm). In some embodiments, maximum upper distance  3692  can be 0.348 inch (9.09 mm). Further, a minimum upper distance  3694  measured as the perpendicular distance from exterior surface  3203  of strikeface  3212  to exterior surface  3203  of third reference point  3424  can range from 0.10 inch to 0.47 inch (0.54 mm to 12 mm). For example, minimum upper distance  3694  can be 0.10 inch (2.54 mm), 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (9 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), or 0.47 inch (12 mm). In some embodiments, minimum upper distance  3694  can be 0.309 inch (7.85 mm). Further still, a maximum lower distance  3696  measured as the perpendicular distance from exterior surface  3203  of strikeface  3212  to exterior surface  3203  of a fourth reference point  3420  located between the lower exterior wall  3427  and the sole  3206  can range from 0.670 inch to 0.98 inch (17 mm to 25 mm). For example, maximum lower distance  3696  can be 0.670 inch (17 mm), 0.709 inch (18 mm), 0.748 inch (19 mm), 0.787 inch (20 mm), 827 inch (21 mm), 0.866 inch (22 mm), 0.906 inch (23 mm), 0.945 inch (24 mm), or 0.98 inch (25 mm). In some embodiments, maximum lower distance  3696  can be 0.863 inch (21.9 mm). In many embodiments, maximum lower distance  3696  is greater than maximum upper distance  3692  and maximum upper distance  3692  is greater than minimum upper distance  3694 . 
     In many embodiments, cavity  3230  can provide an increase in golf ball speed over golf club head  1200 , or other standard golf club heads, can reduce the spin rate of standard hybrids club heads, and can increase the launch angle over both the standard hybrid and iron club heads. In many embodiments, the shape of cavity  3230  determines the level of spring and timing of the response of golf club head  3200 . When the golf club ball impacts strikeface  3212  of club head  3200  with cavity  3230 , strikeface  3212  springs back like a drum, and a rear  3210  bends in a controlled buckle manner. In many embodiments, top rail  3215  can absorb more stress over greater volumetric space than a top rail in a golf club head without cavity  3230 . The length, depth and width of cavity  3230  can vary. These parameter provide control regarding how much spring back is present in the overall design of club head  3200 . 
     Upon impact with the golf ball, strikeface  3212  can bend inward at a greater distance than on a golf club without cavity  3230 . In some embodiments, strikeface  3212  has a 10% to a 50% greater deflection than a strikeface on a golf club head without cavity  3230 . In some embodiments, strikeface  3212  has a 5% to 40% or a 10% to a 20% greater deflection than a strikeface on a golf club head without cavity  3230 . For example, strikeface  3212  can have a 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40% greater deflection than a strikeface on a golf club head without cavity  3230 . In many embodiments, there is both a greater distance of retraction by strikeface  3212  due to the hinge and bending of cavity  3230  over a standard strikeface that does not have a back portion of the club with the cavity. 
     In many embodiments, the face deflection is greater with club head  3200  having cavity  3230 , as a greater buckling occurs at first inflection angle  3486  of top wall  3219  upon impact with a golf ball. Cavity  3230 , however, provides a greater dispersion of stress along top rail  3215 , rear wall  3423 , and top wall  3219 , and the spring back force is transferred from cavity  3230  and first inflection point  3486  of top wall  3219  to strikeface  3212 . A standard top rail, rear wall and top wall without a cavity does not have this hinge/buckling effect, nor does it absorb a high level of stress over a large volumetric area of the top rail, rear wall and top wall. Therefore, the standard strikeface does not contract and then recoil as much as strikeface  3212 . Further, both a larger region of strikeface  3212 , top rail  3215 , rear wall  3423 , and top wall  3219  absorb more stress than the same crown region of a standard golf club head with a standard top rail, top wall and no cavity. In many embodiments, although there is greater stress along a greater area above cavity  3230  that the same area in a standard club without the cavity, the durability of the club head with without the cavity is the same. By adding more spring to the back end of the club (due to inward inclination of a portion of top wall  3219  toward strikeface  3212 ), more force is displaced throughout the volume of the structure. The stress is observed over a greater area of strikeface  3212 , top rail  3215 , rear wall  3423 , and top wall  3219  of golf club head  3200 . Peak stresses can be seen in the standard top rail club head. However, more peak stresses are seen in golf club head  3200  but distributed over a large volume of the material. The hinge and bend regions of golf club head  3200  (i.e., the region above cavity  3230  and cavity  3230  itself) will not deform as long as the stress does not meet the critical buckling threshold. Cavity  3230  and its placement can be designed to be under the critical K value of the buckling threshold. 
     As shown in  FIG.  22   , a further deflection feature of the golf club head  3200  can be the uniform thinned region  3660 , located at the sole  3206  and stretching between the rear  3210  of the body  3201  and the strikeface  3212 , toward a cascading sole portion of the sole (as described in greater detail below). The uniform thinned region  3660  can provide multiple benefits. First, the uniform thinned region  3660  can reduce stress on the strikeface  3212  caused during impact with the golf ball. Second, the uniform thinned region  3660  can bend allowing the strikeface  3212  to experience greater deflection. Third, the uniform thinned region  3660  removes weight from the sole area, allowing the weight to be redistributed more toward the rear of the golf club head  3200 . At impact, the energy imparted to the strikeface  3212  by the golf ball can cause the uniform thinned region  3660  to bend outward, which in turn increases the strikeface  3212  deflection. After bending, the uniform thinned region  3660  rebounds back to its original position returning the majority of the energy from impact back to the golf ball. The result is the golf club head  3200  imparts increased ball speeds and greater travel distances to the golf ball after impact. 
     In some embodiments, body  3201  can comprises stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, body  3201  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, strikeface  3212  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, strikeface  3212  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, body  2701  can comprise the same material as strikeface  3212 . In some embodiments, body  2701  can comprise a different material than strikeface  3212 . 
       FIG.  23    illustrates a back perspective view of an embodiment of golf club head  3700  and  FIG.  24    illustrates a back heel-side perspective view of golf club head  3700  according to the embodiment of  FIG.  23   . In some embodiments, golf club head  3700  can be similar to golf club head  1000  ( FIG.  1   ), golf club head  2200  ( FIG.  8   ), golf club head  2700  ( FIG.  13   ), and/or golf club head  3200  ( FIG.  18   ). Golf club head  3700  can be an iron-type golf club head. In other embodiments, golf club head  3700  can be a hybrid-type, or a fairway wood-type golf club head. In some embodiments, golf club head  3700  does not comprise a badge or a custom tuning port. 
     Golf club head  3700  comprises a body  3701 . In some embodiments, body  3701  can be similar to body  1001  ( FIG.  1   ), body  2201  ( FIG.  8   ), body  2701  ( FIG.  13   ), and/or body  3201  ( FIG.  18   ). In some embodiments, the body  3701  is hollow with an internal cavity  3716 . In other embodiments, the body is at least partially hollow. In embodiments wherein body  3701  is hollow or partially hollow, body  3701  can comprises a volume void of internal cavity  3716  ranging from 1.71 inches 3  (28 cc) to 2.3 inches 3  (37.69 cc). In some hollow and partially hollow embodiments, body  3701  can comprise a volume of 1.70 inches 3  (27.86 cc), 1.80 inches 3  (29.50 cc), 1.90 inches 3  (31.14 cc), 2.00 inches 3  (32.77 cc), 2.10 inches 3  (34.41 cc) 2.20 inches 3  (36.05 cc), or 2.30 inches 3  (37.69 cc). Body  3701  further comprises an exterior surface  3703 , a strikeface  3712 , a heel region  3702 , a toe region  3704  opposite the heel region  3702 , a sole  3706 , a top rail  3715 , and a rear  3710 . 
     Body  3701  of  FIGS.  23 - 29    further comprises a blade length  3725 , a toe edge  3726 , and a strikeface end  3727 . The toe edge  3726  is the farthest edge of the strikeface  3712  at the toe region  3704 , and the strikeface end  3727  is the end of the strikeface  3712  at the heel region  3702 , right before the strikeface  3712  integrally curves into the hosel. As illustrated in  FIG.  29   , blade length  3725  is the distance measured from the toe edge  3726  to the strikeface end  3727 . The blade length  3725  is measured parallel to the flat surface of the strikeface  3712  between the toe edge  3726  and the strikeface end  3727  at the heel end  3702  before the strikeface  3712  integrally curves with the hosel. The blade length of the body  3701  can range from 2.70 inch (6.86 cm) to 3.00 inch (7.62 cm). For example, in some embodiments the body  3701  can comprise a blade length of 2.74 inch (6.96 cm), 2.78 inch (7.06 cm), 2.82 inch (7.16 cm), 2.86 inch (7.26 cm), 2.90 inch (7.37 cm), 2.94 inch (7.47 cm), 2.98 inch (7.57 cm), or 3.00 inch (7.62 cm). 
     The body  3701  further comprises a uniform thinned region transitioning from the bottom of the strikeface  3712  to the sole  3706 , toward a cascading sole portion of the sole (as described in greater detail below). In the illustrated embodiment, the uniform thinned region comprises a sole thickness measured perpendicular from the exterior surface  3703  to an interior surface  3919  at the uniform thinned region, which can remain constant from the bottom of the strikeface  3712  to adjacent the cascading sole portion of the sole. In some embodiments, the sole thickness of the uniform thinned region can be thinner than a conventional sole. For example, in some embodiments, the sole thickness of the uniform thinned region may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness of the uniform thinned region may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness of the uniformed thinned region can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
       FIG.  25    illustrates a cross-section of golf club head  3700  along the cross-sectional line XXXIX-XXXIX in  FIG.  23   , according to one embodiment. As seen in  FIG.  25   , strikeface  3712  comprises a high region  3976 , a middle region  3974 , and a low region  3972 . Rear  3710  can comprise an upper region  3711 , a lower region  3713 , and a cavity  3730 . 
     Upper region  3711  of rear  3710  comprises top rail  3715 , a rear wall  3923 , a top wall  3719 , and a back wall  3921 . In many embodiments, the rear wall  3923  of rear  3710  is located below and adjacent to the top rail  3715 , the top wall  3719  of rear  3710  is located below and adjacent to the rear wall  3923 , and the back wall  3721  is located below and adjacent to the top wall  3719 . Upper region further comprises a first reference point  3922  located between top rail  3715  and rear wall  3923 , a second reference point  3982  located between rear wall  3923  and top wall  3719 , a first inflection point  3986  located between top wall  3719  and back wall  3921 , and a second inflection point  3992  located between the back wall  3921 , and a bottom incline  3925  of the lower region  3713 . First reference point  3922  and second reference point  3982  create a reference line  3939  as illustrated in  FIG.  26   . 
     The top wall  3719  is angled toward the strikeface and away from the top rail  3715  in a direction toward the first inflection point  3986 . The described configuration of the top wall  3719  allows increased bending of the top rail  3715  of the club head  3700  on impact with a golf ball, compared with a club head devoid of the described top wall configuration. 
     Cavity  3730  is located on the exterior surface  3703 , below top rail  3715  and rear wall  3923 , above the lower region  3713  of rear  3710 , and is defined by at least in part by upper region  3711  and lower region  3713 . 
     In some embodiments, top rail  3715  of the upper region  3711  can be a flatter and taller top rail or skirt than in irons known to one skilled in the art. The flatter and taller rail can compensate for mishits of strikeface  3712  to increase playability off the tee. In some embodiments, the length of top rail  3715 , measured from heel region  3702  to toe region  3704 , can be 70% to 95% of the length of golf club head  3700 . In many embodiments, cavity  3730  comprises a top rail box spring design. For some fairway iron-type golf club head embodiments, cavity  3730  can be a reverse scoop or indentation of rear  3710  with body  3701  comprising a greater thickness toward sole  3706 . In many embodiments, top rail  3715  and cavity  3730  provide an increase in the overall bending of strikeface  3712 . In some embodiments, the bending of strikeface  3712  can allow for a 2% to 5% increase of energy. Cavity  3730  allows for strikeface  3712  to be thinner and allow additional overall bending. 
     Strikeface  3712  of body  3701  comprises a thickness  3954  measured perpendicularly to strikeface  3712  from the exterior surface  3703  to the interior surface  3919 . The thickness  3954  of the strikeface  3712  can range from 0.060 inch to 0.110 inch. For example, the thickness  3954  of the strikeface  3712  can be 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, 0.080 inch, 0.085 inch, 0.090 inch, 0.095 inch, 0.100 inch, 0.105 inch, or 0.110 inch. In some embodiments, thickness  3954  of strikeface  3712  can remain constant from heel region  3702  to toe region  3704 , and/or from top rail  3715  to sole  3706 . In other embodiments, thickness  3954  of strikeface  3712  can vary from heel region  3702  to toe region  3704 , and/or from top rail  3715  to sole  3706 . For example, the thickness  3954  of strikeface  3712  can be greatest at a central portion of strikeface  3712  near the middle region  3974 , and taper along the periphery of strikeface  3712  near the high region  3976 , and the low region  3972 . In many embodiments, the center of the strikeface  3712  near the middle region  3974  can have a thickness  3954  of 0.100 inch and the periphery of the strikeface  3712  can have a thickness  3954  of 0.080 inch. In other examples, the thickness  3954  can increase, or decreases, or any variation thereof starting at a central region near the middle region  3974  of strikeface  3712  and extending toward the periphery near the high region  3976  and the low region  3972 . 
     Golf club head  3700  further comprises a height  3980  for rear wall  3923  of upper region  3711  of rear  3710  measured from first reference point  3922  to second reference point  3982 . In some embodiments, height  3980  of rear wall  3923  of upper region  3711  of rear  3710  can range from 0.115 inch (0.292 cm) to 0.250 inch (0.635 cm), 0.130 inch (0.330 cm) to 0.200 inch (0.508 cm), or 0.150 inch (0.381 cm) to 0.180 inch (0.457 cm). For example, in some embodiments, the height  3980  of rear wall  3923  of the upper region  3711  of rear  3710  can be 0.115 inch (0.292 cm), 0.125 inch (0.318 cm), 0.135 inch (0.343 cm), 0.145 inch (0.368 cm), 0.155 inch (0.394 cm), 0.165 inch (0.419 cm), 0.175 inch (0.445 cm), 0.185 inch (0.470 cm), 0.195 (0.495 cm), or 0.250 inch (0.635 cm). In some embodiments, the height  3980  of rear wall  3923  of the upper region  3711  of rear  3710  can range from 0.150 inch (0.381 cm) to 0.210 inch (0.533 cm). In some embodiments, the height  3980  of rear wall  3923  of the upper region  3711  of rear  3710  can be 0.166 inch (0.422 cm). In some embodiments, the height  3980  of rear wall  3923  of upper region  3711  of rear  3710  can range from 3% to 15% of the height of the golf club head  3700 . 
     The height  3980  of rear wall  3923  of the upper region  3211  of rear  3210 , as described herein, allows cavity  3730  to absorb at least a portion of the stress on strikeface  3712  during impact with a golf ball. A golf club head having a rear wall height greater than rear wall height  3980  described herein would absorb less stress (and allow less strikeface deflection) in impact than golf club head  3700  described herein, due to increased dispersion of the impact stress along the top rail prior to reaching the cavity. 
     Rear wall  3923  further comprises a thickness measured perpendicularly from the exterior surface  3703  to the interior surface  3919  of the rear wall  3923 . The thickness of the rear wall  3923  can range from 0.037 inch to 0.058 inch, 0.037 inch to 0.048 inch, or 0.042 inch to 0.058 inch. For example, the thickness of the rear wall  3923  can be 0.037 inch, 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.052 inch, 0.055 inch, or 0.058 inch. The thickness of the rear wall  3923  can aid in stress distribution as well as increase the bending of the strikeface  3712 . 
     In many embodiments, second reference point  3982  of upper region  3711  of rear  3710  can have a distance ranging from 0.150 inch (0.381 cm) to 1.00 inch (2.54 cm), 0.150 inch (0.381 cm) to 0.350 inches (0.457 cm), 0.300 inch (0.457 cm) to 0.500 inch (1.27 cm), 0.450 inch (1.14 cm) to 0.650 inch (1.65 cm), 0.600 inch (1.52 cm) to 0.800 inch (2.03 cm), or 0.750 inch (1.91 cm) to 1.00 inch (2.54 cm) from apex  3928  of top rail  3715 . For example, the second reference point  3982  of upper region  3711  can be 0.150 inch (0.381 cm), 0.450 inch (1.14 cm), 0.600 inch (1.52 cm), 0.750 inch (1.91 cm), 0.900 inch (2.29 cm), or 1.000 inch (2.54 cm) below the apex  3428  of top rail  3215 . 
     Golf club head  3700  further comprises a length  3988  of top wall  3719  of upper region  3711 , measured from the second reference point  3982  to first inflection point  3986 . In many embodiments, top wall length  3988  can range from 0.030 inch (0.076 cm) to 0.100 inch (0.254 cm). In many embodiments, top wall length  3988  can range from 0.030 inch (0.076 cm) to 0.050 inch (0.127 cm), 0.040 inch (0.102 cm) to 0.060 inch (0.152 cm), 0.050 (0.127 cm) to 0.080 inch (0.203 cm), or 0.070 inch (0.178 cm) to 0.100 inch (0.254 cm). For example, top wall length  3988  can be 0.030 inch (0.076 cm), 0.035 inch (0.089 cm), 0.040 inch (0.102 cm), 0.045 inch (0.114 cm), 0.050 inch (0.127 cm), 0.055 inch (0.140 cm), 0.060 inch (0.152 cm), 0.065 inch (0.165 cm), 0.070 inch (0.178 cm), 0.075 inch (0.191 cm), 0.080 inch (0.203 cm), 0.085 inch (0.216 cm), 0.090 inch (0.229 cm), 0.095 inch (0.241 cm), or 0.100 inch (0.254 cm). 
     In a number of embodiments, a portion of top wall  3719  of upper region  3711  extends away from rear wall  3923  at second reference point  3982 , toward strikeface  3712  at first inflection point  3986 . In some embodiments, the portion of top wall  3719  extending away from rear wall  3923  toward strikeface  3712  can be straight, curved upward, or curved downward. This orientation of top wall  3719  creates a buckling point, hinge point or plastic hinge to direct the stress of impact toward cavity  3730  and to allow increased flexing of strikeface  3712  during impact. 
     The first inflection point  3986  of the upper region  3711 , can have a distance from the first reference point  3922  ranging from 0.20 inch (0.508 cm) to 1.0 inch (2.54 cm), or 0.5 inch (1.27 cm) to 0.7 inch (1.778 cm). For example, the first inflection point  3986  can be 0.20 inch (0.508 cm), 0.25 inch (0.635 cm), 0.30 inch (0.762 cm), 0.35 inch (0.889 cm), 0.40 inch (1.016 cm), 0.45 inch (1.143 cm), 0.50 inch (1.27 cm), 0.55 inch (1.397 cm), 0.60 inch (1.524 cm), 0.65 inch (1.651 cm), 0.70 inch (1.778 cm), 0.75 inch (1.905 cm), 0.80 inch (2.032 cm), 0.85 inch (2.159 cm), 0.90 inch (2.286 cm), 0.95 inch (2.413 cm), or 1.0 inch (2.54 cm) below the first reference point  3922 . 
     In some embodiments, upper region  3711  further comprises an inflection angle  3996  measured from top wall  3719  to back wall  3921 , wherein inflection angle  3996  can range from 70 degrees to 150 degrees. In some embodiments, inflection angle  3996  of upper region can range from 90 degrees to 130 degrees. In some embodiments, inflection angle  3996  of upper region can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, or 150 degrees. In many embodiments, inflection angle  3996  of upper region allows first inflection point  3986  to act as a buckling point or plastic hinge upon golf club head  3700  impacting the golf ball at strikeface  3712 . In some embodiments, the wall thickness at the first inflection point  3986  can be thinner than at the top wall  3719  and back wall  3921 . 
     In some embodiments, back wall  3921  of cavity  3730  of upper region  3711  can have a back wall length  3990  measured from first inflection point  3986  to second inflection point  3992 . In a number of embodiments, back wall length  3990  can range from 0.100 inch (0.254 cm) to 0.350 inch (0.889 cm). In many embodiments, back wall length  3990  can be 0.100 inch (0.254 cm), 0.125 inch (0.318 cm), 0.150 inch (0.381 cm), 0.175 inch (0.445 cm), 0.200 inch (0.508 cm), 0,225 inch (0.572 cm), 0,250 inch (0.635 cm), 0,275 inch (0.699 cm), 0,300 inch (0.762 cm), 0,325 inch (0.826 cm), or 0,350 inch (0.889 cm). 
     The back wall  3921  of the cavity  3730  can further comprise a thickness measured perpendicularly from the interior surface  3919  to the exterior surface  3703  of the back wall  3921 . The thickness of the back wall  3921  can range from 0.028 inch to 0.039 inch, 0.028 inch to 0.032 inch, or 0.032 inch to 0.039 inch. For example, the thickness of the back wall  3921  can be 0.028 inch, 0.030 inch, 0.032 inch, 0.034 inch, 0.035 inch, 0.037 inch, or 0.039 inch. The thickness of the back wall  3921  can help distribute stress and increase the bending of the strikeface  3712 . 
     In some embodiments, the maximum height of the back wall  3921  of the upper region  3711 , measured perpendicular to a ground plane  3903  when golf club head  3700  is at address, to first inflection point  3986 , can range from 0.25 inch (0.635 cm) to 3 inches (7.62 cm), or 0.50 inch (1.27 cm) to 2 inches (5.08 cm). For example, the first inflection point  3986  can be 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch 1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), 1.25 inches (3.18 cm), 1.375 inches (3.49 cm), 1.5 inches (3.81 cm), 1,625 inches (4.12 cm), 1.75 inches (4.45 cm), 1.875 inches (4.76 cm), 2.0 inches (5.08 cm), 2.125 inches (5.40 cm), 2.25 inches (5.71 cm), 2.375 inches (6.03 cm), 2.5 inches (6.35 cm), 2.625 inches (6.67 cm), 2.75 inches (7.00 cm), 2.875 inches (7.30 cm) or 3.0 inches (7.62 cm) above a lowest point of sole  3706  to the ground plane  3903  when golf club head  3700  is at address. 
     In many embodiments, second inflection point  3992  of cavity  3730  of upper region  3711 , adjacent to bottom incline  3925  of lower region  3713 , can have a distance from apex  3928  of top rail  3715  ranging from at least 0.25 inch (0.635 cm) to 2.0 inches (5.08 cm), or 0.5 inch (1.27 cm) to 1.5 inches (3.81 cm). For example, the second inflection point  3992  can be at least 0.25 inch (0.635 cm), 0.5 inch (1.27 cm), 0.75 inch (1.91 cm), 1.0 inch (2.53 cm), 1.25 inches (3.18 cm), 1.75 inches (4.45 cm), or 2.0 inches (5.08 cm) below the apex  3928  of top rail  3715 . 
     In some embodiments as illustrated in  FIG.  23   , cavity  3730  of upper region  3711  can comprise at least one channel  3739 . In many embodiments, channel  3739  extends from heel region  3702  to toe region  3704 . Channel  3739  comprises a channel width  3932  measured from back wall  3921  to the second reference point  3982  substantially parallel to ground plane  3903 , where channel width can vary in a direction from top rail  3215  to sole  3206 . In some embodiments as illustrated in  FIG.  23   , channel width  3932  can range from 0.039 inch (1 mm) to 0.590 inch (15 mm), or 0.150 inch (3.81 mm) to 0.400 inch (10.16 mm). For example, channel width  3932  can be 0.039 inch (1.0 mm), 0.079 inch (2 mm), 0.12 inch (3 mm), 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.39 inch (10 mm), or 0.59 inch (15 mm). In other embodiments, a channel toe region width of channel  3739  is less than a channel heel region width of channel  3739 . In other embodiments, the channel heel region width is less than the channel toe region width. In other embodiments, a channel middle region width of channel  3739  can be less than at least one of the channel heel region width or the channel toe region width. In other embodiments, the channel middle region width can be greater than at least one of the channel heel region width or the channel toe region width. In some embodiments, channel  3739  is symmetrical from heel to toe. In other embodiments, channel  3739  is non-symmetrical. In other embodiments, channel  3739  can further comprise at least toe partial channels. In some embodiments, channel  3739  can comprise a series of partial channels interrupted by one or more bridges. In some embodiments, the one or more bridges can be approximately the same thickness as the thickness of top rail  3715 . 
     Channel width  3932 , as described herein, allows absorption of stress from strikeface  3712  on impact. A golf club head having a channel width less than the channel width  3932  described here (e.g., a golf club head with a less pronounced cavity) would allow less stress absorption from the strikeface on impact (due to less material on the upper region  3711  of rear  3710 ), and therefore would experience less strikeface deflection than golf club head  3700  described herein. 
     In many embodiments, back cavity  3730  further comprises a back cavity angle  3935 . Back cavity angle  3935  is measured from reference line  3939  to top wall  3719 . In many embodiments, back cavity angle  3935  can range from 5 degrees to 80 degrees. In some embodiments, back cavity angle  3935  can be 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, or 80 degrees. 
     In some embodiments, back wall  3921  of cavity  3730  of upper region  3711  can further comprise a planar surface. In other embodiments, at least a portion of back wall  3921  can comprise a protrusion  3940  extending outward, away from strike face  3712 . At least a portion of back wall  3921  comprising protrusion  3940  can range from 15% to 100%. For example, at least 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of back wall  3921  can comprise protrusion  3940 . Protrusion  3940  can be positioned on at least a portion of back wall  3921  closer to toe region  3704 , closer to heel region  3702 , closer to lower exterior wall  3927 , closer to top wall  3719 , or centered on the back wall  3921 . Protrusion  3940  comprises a length  3942 , measured from heel region  3702  to toe region  3704 , and a width  3944 , measured from top rail  3715  to sole  3706 . 
     The protrusion  3940  can comprise a thickness measured perpendicularly from the interior surface  3919  to the exterior surface  3703  of the protrusion  3940 . The thickness of the protrusion  3940  can range from 0.028 inch to 0.045 inch, 0.028 inch to 0.032 inch, 0.032 inch to 0.039 inch, or 0.039 inch to 0.045 inch. For example, the thickness of the back wall  3921  can be 0.028 inch, 0.030 inch, 0.032 inch, 0.034 inch, 0.035 inch, 0.037 inch, 0.039 inch, 0.041 inch, 0.043 inch, or 0.045 inch. The thickness of the protrusion  3940  can help distribute stress and increase the bending of the strikeface  3712 . 
       FIG.  26    illustrates a view of top rail  3715  and a portion of rear  3710  of the cross-section of golf club head  3700  of  FIG.  23   , along a cross-sectional line IX-IX in  FIG.  23    that is similar to the cross-section of  FIG.  25   . In many embodiments, golf club head  3700  comprises a rear angle  4040 , a top rail angle  4045 , and a strikeface angle  4050 . Rear angle  4040  is measured from top wall  3719  to rear wall  3923  of upper region  3711 . In many embodiments, rear angle  4040  can range from 70 degrees to 140 degrees. In some embodiments, rear angle  4040  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, or 140 degrees. Top rail angle  4045  is measured from rear wall  3923  of upper region  3711  to top rail  3715 . In many embodiments, top rail angle  4045  can range from 35 degrees to 120 degrees or 70 degrees to 110 degrees. In some embodiments, top rail angle  4045  can be 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, or 120 degrees. Strikeface angle  4050  is measured from strikeface  3712  to top rail  3715 . In many embodiments, strikeface angle  4050  can range from 70 degrees to 160 degrees or 70 degrees to 110 degrees. In some embodiments, strikeface angle  4050  can be 70 degrees, 75 degrees, 80 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, or 160 degrees. 
     The upper region  3711  further comprises a minimum gap  4090  measured as a perpendicular distance from an inner surface of the cavity at the first inflection point  3986  to the inner surface  3919  of strikeface  3712 . In some embodiments, minimum gap  4090  can range from 0.079 inch (2 mm) to 0.24 inch (6 mm). For example, minimum gap  4090  can be 0.079 inch (2 mm), 0.118 inch (3 mm), 0.16 inch (4 mm), 0.197 inch (5 mm) or 0.24 inch (6 mm). In other embodiments, minimum gap  4090  can range from 0.118 inch (3 mm) to 0.16 inch (4 mm). In some embodiments, minimum gap  4090  can be 0.135 inch (3.429 mm). 
     Lower region  3713  of rear  3710  of body  3701  comprises the bottom incline  3925 , and a lower exterior wall  3927 . The lower exterior wall  3927  is located below and adjacent the bottom incline  3925 . A third inflection point  3994  is located between the bottom incline  3925  and the lower exterior wall  3927 . A third reference point  3920  is located between lower exterior wall  3927  and sole  3706 . 
     A top portion of the lower exterior wall  3927  of the lower region  3713  can comprise a thickness. The thickness of the top portion of the lower exterior wall  3927  can be measured perpendicular from the interior surface  3919  to the exterior surface  3703  of the top portion of the lower exterior wall  3927 . The thickness of the top portion of the lower exterior wall  3827  can range from 0.037 inch to 0.058 inch, 0.037 inch to 0.048 inch, or 0.042 inch to 0.058 inch. For example, the thickness of the top portion of the lower exterior wall  3827  can be 0.037 inch, 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.052 inch, 0.055 inch, or 0.058 inch. The thickness of the top portion of the lower exterior wall  3827  can aid in stress distribution as well as increase the bending of the strikeface  3712 . 
     In some embodiments, bottom incline  3925  of lower region  3713  comprises a bottom incline length  3929 . Bottom incline length  3929  is measured from second inflection point  3992  to the third inflection point  3994 . In a number of embodiments, bottom incline length  3994  can range from 0.010 inch (0.025 cm) to 0.210 inch (0.533 cm), 0.010 inch (0.025 cm) to 0.050 inch (0.127 cm), 0.050 inch (0.127 cm) to 0.100 inch (0.254 cm), 0.100 inch (0.254 cm) to 0.150 inch (0.381 cm), or 0.150 inch (0.381 cm) to 0.210 inch (0.533 cm). In many embodiments, bottom incline length  3929  can be 0.010 inch (0.025 cm), 0.030 inch (0.076 cm), 0.050 inch (0.127 cm), 0.070 inch (0.178 cm), 0.090 inch (0.229 cm), 0.110 inch (0.279 cm), 0.130 inch (0.330 cm), 0.150 inch (0.381 cm), 0.160 inch (0.406 cm), 0.170 inch (0.432 cm), 0.180 inch (0.457 cm), 0.190 inch (0.483 cm), 0.200 inch (0.508 cm), or 0.210 inch (0.533 cm). In some embodiments, the bottom incline length  3929  can vary from heel region  3702  to toe region  3704 . In other embodiments, the bottom incline length  3929  can remain constant from heel region  3702  to toe region  3704 . 
     In some embodiments, the maximum height of bottom incline  3925 , measured perpendicular from ground plane  3903  when body  3701  is at address, to second inflection point  3992 , can be 0.25 inches (0.635 cm) to 3 inches (7.62 cm), 0.05 inch (1.27 cm) to 2 inches (5.08 cm) above ground  3903 . For example, the second inflection point  3992  can be 0.25 inch (0.635 cm), 0.375 inch (0.953 cm), 0.5 inch (1.27 cm), 0.625 inch (1.59 cm), 0.75 inch (1.91 cm), 0.825 inch (2.10 cm), 1.0 inch (2.54 cm), 1.125 inches (2.88 cm), 1.25 inches (3.18 cm), 1.375 inches (3.49 cm), 1.5 inches (3.81 cm), 1.625 inches (4.12 cm), 1.75 inches (4.45 cm), 1.875 inches (4.76 cm), 2.0 inches (5.08 cm), 2.125 inches 5.40 cm), 2.25 inches (5.71 cm), 2.375 inches (6.03 cm), 2.5 inches (6.35 cm), 2.625 inches (6.67 cm), 2.75 inches (7.00 cm), 2.875 inches (7.30 cm), or 3.0 inches (7.62 cm) above ground  3903 . 
     In some embodiments, lower region  3713  further comprises a lower angle  3951  measured from between the bottom incline  3925  of lower region  3713  and lower exterior wall  3927  of lower region  3710 , as illustrated in  FIG.  27   . In some embodiments, lower angle  3951  can be less than 180 degrees. In a number of embodiments, lower angle  3951  can be 30 degrees to 160 degrees, or 70 degrees to 130 degrees. For example, lower angle  3951  can be 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, 90 degrees, 100 degrees, 110 degrees, 120 degrees, 130 degrees, 140 degrees, 150 degrees, or 160 degrees. 
     In some embodiments, lower region  3713  further comprises a bottom incline angle  3905  measured from bottom incline  3925  to ground  3903 . Bottom incline angle  3905  can range from 15 degrees to 45 degrees. In some embodiments, bottom incline angle  3905  can be 15 degrees, 16 degrees, 17 degrees, 18 degrees, 19 degrees, 20 degrees, 21 degrees, 22 degrees, 23 degrees, 24 degrees, 25 degrees, 26 degrees, 27 degrees, 28 degrees, 29 degrees, 30 degrees, 31 degrees, 32 degrees, 33 degrees, 34 degrees, 35 degrees, 36 degrees, 37 degrees, 38 degrees, 39 degrees, 40 degrees, 41 degrees, 42 degrees, 43 degrees, 44 degrees, or 45 degrees. 
       FIG.  27    illustrates a simplified cross-sectional view of golf club head  3700 , similar to the detailed cross-section of golf club head  3700  illustrated in  FIG.  25   . Golf club head  3700  include cavity  3730 , upper region  3711 , lower region  3713 , and exterior surface  3703 . In many embodiments, a maximum upper distance  4192  measured as the perpendicular distance from exterior surface  3703  of strikeface  3712  to exterior surface  3703  of second reference point  3982  of upper region  3711  can range from 0.20 inch to 0.59 inch (5 mm to 15 mm). For example, maximum upper distance  4192  can be 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (8.89 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), 0.47 inch (12 mm), 0.51 inch (13 mm), 0.55 inch (14 mm), or 0.59 inch (15 mm). In some embodiments, maximum upper distance  4192  can be 0.348 inch (9.09 mm). Further, a minimum upper distance  4194  measured as the perpendicular distance from exterior surface  3703  of strikeface  3712  to the exterior surface  3703  of the back wall  3921  at the first inflection point  3986  can range from 0.16 inch to 0.47 inch (4 mm to 12 mm). For example, minimum upper distance  4194  can be 0.16 inch (4 mm), 0.20 inch (5 mm), 0.24 inch (6 mm), 0.28 inch (7 mm), 0.31 inch (8 mm), 0.35 inch (9 mm), 0.39 inch (10 mm), 0.43 inch (11 mm), or 0.47 inch (12 mm). In some embodiments, minimum upper distance  4194  can be 0.309 inch (7.85 mm). Further still, a maximum lower distance  4196  measured as the perpendicular distance from exterior surface  3703  of strikeface  3712  to exterior surface  3703  of third reference point  3920  of lower region  3713  can range from 0.670 inch to 0.98 inch (17 mm to 25 mm). For example, maximum lower distance  4196  can be 0.670 inch (17 mm), 0.709 inch (18 mm), 0.748 inch (19 mm), 0.787 inch (20 mm), 827 inch (21 mm), 0.866 inch (22 mm), 0.906 inch (23 mm), 0.945 inch (24 mm), or 0.98 inch (25 mm). In some embodiments, maximum lower distance  4196  can be 0.863 inch (21.9 mm). In many embodiments, maximum lower distance  4196  is greater than maximum upper distance  4192  and maximum upper distance  4192  is greater than minimum upper distance  4194 . 
     As illustrated in  FIGS.  25 - 27   , body  3701  is a hollow body club head that further comprises internal cavity  3716 . Internal cavity  3716  of the body  3701  comprises a volume. The volume of the internal cavity  3716  can range from 0.70 inch 3  (11.47 cc) to 1.70 inches 3  (27.86 cc). In some embodiments, the internal cavity  3716  can comprise a volume of be 0.70 inch 3  (11.47 cc), 0.80 inch 3  (13.11 cc), 0.90 inch 3  (14.75 cc), 1.00 inch 3  (16.39 cc), 1.10 inches 3  (18.03 cc), 1.20 inches 3  (19.66 cc), 1.30 inches 3  (21.30 cc), 1.40 inches 3  (22.94 cc), or 1.50 inches 3  (24.58 cc), 1.60 inches 3  (26.22 cc), or 1.70 inches 3  (27.86 cc). 
     The internal cavity  3716  of the body  3701  further comprises interior surface  3919 . In some embodiments, interior surface  3919  of rear  3710  is a planar and smooth surface. In other embodiments as illustrated in  FIG.  28   , the interior surface  3919  of the internal cavity  3716  of rear  3710  comprises a plurality of ribs  3952 . The plurality of ribs  3952  extend in a direction from top rail  3715  toward sole  3706 . Plurality of ribs  3952  can be located anywhere on interior surface  3919  of rear  3710 . In some examples, plurality of ribs  3952  can be positioned onto a portion of interior surface  3919  of lower exterior wall  3927 . In other examples, plurality of ribs  3952  can be position on a portion of interior surface  3919  of rear wall  3923 . In some embodiments, plurality of ribs  3952  can be positioned on a portion of interior surface  3919  of rear  3710  and can extend into another portion of the rear  3710 . For example, plurality of ribs  3952  are positioned on a portion of interior surface  3919  of rear wall  3923  and can extend up to at least a portion of the interior surface  3919  of top wall  3719 , at least a portion of back wall  3921 , or at least a portion of lower exterior wall  3927 . The plurality of ribs  3952  can comprise between 1 to 8 ribs. For example, the plurality of ribs  3952  can comprise one rib  3952 , two ribs  3952 , three ribs  3952 , four ribs  3952 , five ribs  3952 , six ribs  3952 , seven ribs  3952 , or eight ribs  3952 . In embodiments having one or more plurality of ribs  3952 , the plurality of ribs  3952  can be spaced equidistance from each other or more concentrated near heel region  3702 , toe region  3704 , top rail  3715 , or sole  3706 . The plurality of ribs  3952  and the location of the plurality of ribs  3952  can help optimize the frequency and amplitude of sound response. 
     In many embodiments, internal cavity  3716  of body  3701  can be void of any substances. In other embodiments, internal cavity  3716  of body  3701  can further comprise a polymer, wherein the polymer can at least partially fill the internal cavity  3716 . The polymer can be polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, polycarbonate, polypropylene, other thermoplastics, composite polymers or any combination thereof. The polymer can fill 10% to 80% 10% to 25%, 15% to 30%, 30% to 45%, 45% to 60%, 60% to 75%, 75% to 80%, 10% to 40%, 30% to 60%, or 40% to 80% of the internal cavity  3716  of the body  3701 . For example, the polymer can fill 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% of the internal cavity  3716  of the body  3701 . In some embodiments, the polymer fills 80% of the internal cavity  3716  of the body  3701 . 
     The polymer comprises a specific gravity ranging from 0.5 to 4. For example, the specific gravity of the polymer can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, or 4. In some embodiments, the specific gravity of the polymer is proportional to the mass of the polymer, wherein 1 specific gravity of the polymer is equal to 1 gram, 2 specific gravity of the polymer is equal to 2 grams and etc. Similarly, in some embodiments, the volume of the polymer is proportional to the polymer specific gravity. For example, the ratio of polymer mass to polymer volume can be 1 g to 1 cc, 2 g to 2 cc, 3 g to 3 cc, or 4 g to 4 cc. However, in other embodiments, while the specific gravity of the polymer is proportional to the polymer mass, the volume does not correlate to the specific gravity. For example, the ratio of polymer mass to polymer volume can be 1 g to 1 cc, 2 g to 0 cc, 3 g to 1 cc, 4 g to 2 cc, 4 g to 3 cc, 3 g to 2 cc, 3 g to 4 cc, or any other suitable ratio. 
     The mass of the polymer allows for the swing weight of the golf club head  3700  to be customizable for each player. Increasing the volume of polymer, and thus the mass, increases the swing weight, while decreasing the volume of polymer decreases the swing weight. Having the appropriate swing weight for each individual player improves feel during a swing and can improve performance such as swing speed, swing path and this ball speed, and ball trajectory. The polymer can further increase the overall mass of the golf club head  3700  more toward the rear  3710  and sole  3706 . Increasing the mass more toward the rear  3710  and sole  3706  can keep the center of gravity low and back, and there improve the moment of the inertia. The polymer can further still act as a dampener to improve sound and absorb shock during impact. 
     The polymer volume when filled within the internal cavity  3716  can range from 0 inch 3  (0 cc) to 1.53 inches 3  (25 cc), 0.244 inch 3  (4 cc) to 1.22 inches 3  (20 cc), 0.305 inch 3  (5 cc) to 0.915 inch 3  (15 cc), 0.122 inch 3  (2 cc) to 0.488 inch 3  (12 cc), or 0.854 inch 3  (14 cc) to 1.34 inch 3  (22 cc). In some embodiments, the polymer volume inside the internal cavity  3716  can be 0 inch 3  (0 cc), 0.244 inch 3  (4 cc), 0.244 inch 3  (8 cc), 0.488 inch 3  (12 cc), 0.976 inch 3  (16 cc), 1.22 inches 3  (20 cc), or 1.53 inches 3  (25 cc). The polymer filled within the internal cavity  3716  can cover a percentage of the interior surface  3919  of the strikeface  3712  ranging from 0% to 100%, 15% to 85%, 30% to 70%, 45% to 60%, 20% to 40%, or 60% to 80%. In some embodiments, the polymer covers 0%, 15%, 30%, 45%, 60%, 75%, 90% or 100% of the interior surface  3919  of the strikeface  3712 . Increasing the percent coverage of the polymer on the interior surface  3919  of the strikeface  3712  increases the support for the strikeface  3712 , thereby allowing for a thinner strikeface  3712 . Thinning the strikeface  3712  can increase the deflection of the strikeface  3712  upon impact with a ball which can impart the ball with increases speed and spin. Thinning the strikeface  3716  also allows for weight to be redistributed elsewhere on the body  3701  to optimize center of gravity and moment of inertia. 
     In some embodiments as illustrated in  FIG.  29   , the golf club head  3700  can further comprise a first aperture  3934  located on toe region  3704  and a second aperture  3936  located in a hosel of the golf club head  3700 . The first aperture  3924  is configured to receive a toe weight (not pictured), wherein the toe weight can range from 2 grams to 7 grams. In some embodiments, the toe weight can be 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, or 7 grams. The second aperture  3936  is configured to receive a tip weight (not pictured), wherein the tip weight can range from 2 grams to 7 grams. In some embodiments, the tip weight can be 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, or 7 grams. In many embodiments, the first aperture  3934  and the second aperture  3936  can further be configured to receive the polymer. The first aperture  3934  can receive 1 gram to 9 grams of polymer (e.g., 1 gram, 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, 7 grams, 8 grams, or 9 grams). Similarly, the second aperture  3936  can receive 1 gram to 9 grams of polymer (e.g., 1 gram, 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, 7 grams, 8 grams, or 9 grams). The toe and tip weight, and the polymer housed within the first aperture  3934  and the second aperture  3936  can affect the swing weight to optimize CG and MOI. 
     In many embodiments, cavity  3730  can provide an increase in golf ball speed over golf club head  1200 , or other standard golf club heads, can reduce the spin rate of standard hybrids club heads, and can increase the launch angle over both the standard hybrid and iron club heads. In many embodiments, the shape of cavity  3730  determines the level of spring and timing of the response of golf club head  3200 . When the golf club ball impacts strikeface  3712  of club head  3700  with cavity  3730 , strikeface  3712  springs back like a drum, and a rear  3710  bends in a controlled buckle manner. In many embodiments, top rail  3715  can absorb more stress over greater volumetric space than a top rail in a golf club head without cavity  3730 . The length, depth and width of cavity  3730  can vary. These parameter provide control regarding how much spring back is present in the overall design of club head  3700 . 
     Upon impact with the golf ball, strikeface  3712  can bend inward at a greater distance than on a golf club without cavity  3730 . In some embodiments, strikeface  3712  has a 10% to a 50% greater deflection than a strikeface on a golf club head without cavity  3730 . In some embodiments, strikeface  3712  has a 5% to 40% or a 10% to a 20% greater deflection than a strikeface on a golf club head without cavity  3730 . For example, strikeface  3712  can have a 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40% greater deflection than a strikeface on a golf club head without cavity  3730 . In many embodiments, there is both a greater distance of retraction by strikeface  3712  due to the hinge and bending of cavity  3730  over a standard strikeface that does not have a back portion of the club with the cavity. 
     In many embodiments, the face deflection is greater with club head  3700  having cavity  3730 , as a greater buckling occurs at first inflection angle  3986  of top wall  3219  upon impact with a golf ball. Cavity  3730 , however, provides a greater dispersion of stress along top rail  3715 , rear wall  3923 , and top wall  3719 , and the spring back force is transferred from cavity  3730  and first inflection point  3986  of top wall  3719  to strikeface  3712 . A standard top rail, rear wall and top wall without a cavity does not have this hinge/buckling effect, nor does it absorb a high level of stress over a large volumetric area of the top rail, rear wall and top wall. Therefore, the standard strikeface does not contract and then recoil as much as strikeface  3712 . Further, both a larger region of strikeface  3712 , top rail  3715 , rear wall  3923 , and top wall  3719  absorb more stress than the same crown region of a standard golf club head with a standard top rail, top wall and no cavity. In many embodiments, although there is greater stress along a greater area above cavity  3730  that the same area in a standard club without the cavity, the durability of the club head with and without the cavity is the same. By adding more spring to the back end of the club (due to inward inclination of a portion of top wall  3719  toward strikeface  3712 ), more force is displaced throughout the volume of the structure. The stress is observed over a greater area of strikeface  3712 , top rail  3715 , rear wall  3923 , and top wall  3719  of golf club head  3700 . Peak stresses can be seen in the standard top rail club head. However, more peak stresses are seen in golf club head  3700  but distributed over a large volume of the material. The hinge and bend regions of golf club head  3700  (i.e., the region above cavity  3730  and cavity  3730  itself) will not deform as long as the stress does not meet the critical buckling threshold. Cavity  3730  and its placement can be designed to be under the critical K value of the buckling threshold. 
     As shown in  FIG.  28   , a further deflection feature of the golf club head  3700  can be the uniform thinned region  4160 , located at the sole  3706  and stretching between the rear  3710  of the body  3701  and the strikeface  3712 , toward a cascading sole portion of the sole (as described in greater detail below). The uniform thinned region  4160  can provide multiple benefits. First, the uniform thinned region  4160  can reduce stress on the strikeface  3712  caused during impact with the golf ball. Second, the uniform thinned region  4160  can bend allowing the strikeface  3712  to experience greater deflection. Third, the uniform thinned region  4160  removes weight from the sole area, allowing the weight to be redistributed more toward the rear of the golf club head  3700 . At impact, the energy imparted to the strikeface  3712  by the golf ball can cause the uniform thinned region to bend outward, which in turn increases the strikeface  3712  deflection. After bending, the uniform thinned region  4160  rebounds back to its original position returning the majority of the energy from impact back to the golf ball. The result is the golf club head  3700  imparts increased ball speeds and greater travel distances to the golf ball after impact. 
     In some embodiments, body  3701  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, body  3701  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, strikeface  3712  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, strikeface  3712  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, body  3701  can comprise the same material as strikeface  3712 . In some embodiments, body  3701  can comprise a different material than strikeface  3712 . 
       FIG.  30    illustrates a back perspective view of an embodiment of golf club head  4400  and  FIG.  31    illustrates a back heel-side perspective view of golf club head  4400  according to the embodiment of  FIG.  30   . In some embodiments, golf club head  4400  can be similar to golf club head  1000  ( FIG.  1   ), golf club head  2200  ( FIG.  8   ), golf club head  2700  ( FIG.  13   ), golf club head  3200  ( FIG.  18   ), and/or golf club head  3700  ( FIG.  23   ). Golf club head  4400  can be an iron-type golf club head. In other embodiments, golf club head  4400  can be a hybrid-type, or a fairway wood-type golf club head. In some embodiments, golf club head  4400  does not comprise a badge or a custom tuning port. 
     Golf club head  4400  comprises a body  4401 . In some embodiments, body  4401  can be similar to body  1001  ( FIG.  1   ), body  2201  ( FIG.  8   ), body  2701  ( FIG.  13   ), body  3201  ( FIG.  18   ), and/or body  3701  ( FIG.  23   ). Body  4401  further comprises an exterior surface  4403 , a strikeface  4412 , a heel region  4402 , a toe region  4404  opposite the heel region  4402 , a sole  4406 , a top rail  4415 , and a rear  4410 . 
     Body  4401  of  FIGS.  44 - 48    further comprises a blade length. The blade length for body  4401  can be measured similar to blade length  3725  as shown and described in  FIG.  29    (i.e., a measurement parallel to the flat surface of the strikeface  3712 , from a toe edge  3726  of the strikeface  3712 , to strikeface end  3727  before the strikeface  3712  integrally curves into the hosel). The blade length of the body  4401  can range from 2.50 inches (6.35 cm) to 2.90 inches (7.37 cm). For example, in some embodiments, the body  3701  can comprise a blade length of 2.50 inch (6.35 cm), 2.54 inch (6.45 cm), 2.58 inch (6.55 cm), 2.62 inch (6.65 cm), 2.66 inch (6.76 cm), 2.70 inch (6.86 cm), 2.74 inch (6.96 cm), 2.78 inch (7.06 cm), 2.82 inch (7.16 cm), 2.86 inch (7.264 cm), or 2.90 inch (7.37 cm). 
     As shown in  FIG.  34   , a further deflection feature of the golf club head  4400  can be the uniform thinned region  4860 , located at the sole  4406  and stretching between the rear  4410  of the body  4401  and the strikeface  4412 , toward a cascading sole portion of the sole (as described in greater detail below). In the illustrated embodiment, the uniform thinned region  4860  comprises a sole thickness measured perpendicular from the exterior surface  4403  to an interior surface  4619  at the uniform thinned region  4860 , which can remain constant from the bottom of the strikeface  4412  to adjacent the cascading sole portion of the sole. In some embodiments, the sole thickness of the uniform thinned region  4860  can be thinner than a conventional sole. For example, in some embodiments, the sole thickness of the uniform thinned region  4860  may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness of the uniform thinned region  4860  may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness of the uniformed thinned region  4860  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
       FIG.  32    illustrates a cross-section of golf club head  4400  along the cross-sectional line XLVI-XLVI in  FIG.  30   , according to one embodiment. As seen in  FIG.  32   , strikeface  4412  comprises a high region  4676 , a middle region  4674 , and a low region  4672 . 
     The strikeface  4412  of the body  4401  further comprises a thickness  4654  measured perpendicularly to the strikeface  4412  from the exterior surface  4403  to an interior surface  4619 . The thickness  4654  of the strikeface  4412  can range from 0.040 inch to 0.100 inch. For example, the thickness  4654  of the strikeface  4412  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.055 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, 0.080 inch, 0.085 inch, 0.090 inch, 0.095 inch, or 0.100 inch. In some embodiments, thickness  4654  of the strikeface  4412  can vary from the heel region  4402  to the toe region  4404 , and/or from the top rail  4415  to the sole  4406 . For example, the thickness  4654  of the strikeface  4412  can be greatest at the central portion near the middle region  4674  of the strikeface  4412 , and taper along the periphery near the high region  4676  and the low region  4672  of strikeface  4412 . In many embodiments, the center of the strikeface  4412  can have a thickness  4654  of 0.090 inch and the periphery of the strikeface  4412  can have a thickness  4654  of 0.070 inch. In other examples, the thickness  4654  can increase, decrease, or any variation thereof starting at the central region near the middle region  4674  of the strikeface  4412  and extending toward the periphery near the high region  4676  and the low region  4672 . 
     The cross-section of golf club head  4400  in  FIG.  32    further illustrates the rear  4410 . The rear  4410  can comprise an upper region  4411 , a lower region  4413 , and an inflection point  4686  disposed between the upper region  4411  and the lower region  4413 . The inflection point  4686  is further located at the junction between the rear wall  4623  and the bottom incline  4625 . The inflection point  4686  is located nearer to the sole of the club head than the top rail  4415 . 
     The upper region  4411  of rear  4410  comprises a top rail  4415 , an apex  4628  of top rail, a rear wall  4623  orientated parallel to the strikeface  4412 , and a first reference point  4622  disposed between the top rail  4415  and the rear wall  4623 . The first reference point  4622  is located at the junction between the top rail  4415  and the rear wall  2623  parallel to the strikeface  4412 . In many embodiments, the rear wall  4623  of upper region  4411  is located below and adjacent the top rail  4415 . 
     In some embodiments, top rail  4415  of the upper region  4411  can be a flatter and taller top rail or skirt than in irons known to one skilled in the art. The flatter and taller rail can compensate for mishits or strikeface  4412  to increase playability off the tee. In some embodiments. The length of top rail  4415 , measured from heel region  4402  to toe region  4404 , can be 70% to 95% of the length of the golf club head  4400 . 
     The top rail  4415  of the upper region  4411  comprises a thickness  4652 . The thickness  4652  of the top rail  4415  can range from 0.040 inch to 0.080 inch. For example, the thickness  4652  of the top rail  4415  can be 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.051 inch, 0.054 inch, 0.057 inch, 0.060 inch, 0.063 inch, 0.066 inch, 0.069 inch, 0.071 inch, 0.074 inch, 0.077 inch, or 0.080 inch. In many embodiments, the thickness  4652  of the top rail  4415  is constant throughout. In other embodiments, the thickness  4652  of the top rail  4415  can vary. In the exemplary embodiment, the thickness  4652  of the top rail  4415  decreases from the strikeface  4412  toward the rear wall  4623 . In many embodiments due to the thickness  4652  of the top rail, top rail  4415  can provide an increase in the overall bending of strikeface  4412 . In some embodiments, the bending of strikeface  4412  can allow for a 2% to 5% increase of energy. 
       FIG.  33    illustrated the top rail  4415  and a portion of the rear  4410  of the cross-section of the golf club head  4400  of  FIG.  32   , different from cross-section of golf club head  1200  as shown in  FIG.  4   . The strike face  4412  further comprises a strikeface angle  4750 . Strikeface angle  4750  is measured from the strikeface  4412  to the top rail  4415 , wherein the strikeface angle  4750  can range from 70 degrees to 160 degrees or 70 degrees to 110 degrees. In some embodiments, strikeface angle  4050  can be 70 degrees, 75 degrees, 80 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, or 160 degrees. 
       FIG.  33    further illustrates the top rail  4415  comprising a top rail angle  4745 . The top rail angle  4745  is measured from rear wall  4623  to the top rail  4415 . In many embodiments, the top rail angle  4745  can range from 35 degrees to 120 degrees or 70 degrees to 110 degrees. In some embodiments, top rail angle  4745  can be 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, or 120 degrees. 
     The rear wall  4623  of the upper region  4411  comprises a height  4680 . The height  4680  of the rear wall  4623  is measured from the first reference point  4622  to the inflection point  4686 , wherein the first reference point  4622  is positioned at the junction between the top rail  4415  and the rear wall  4623  parallel to the strikeface  4412 . The height  4680  of the rear wall  4623  can range from 0.055 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.080 in to 0.085 or 0.55 inch to 0.85 inch. For example, the height  4680  of the rear wall  4623  can be 0.55 inch, 0.58 inch, 0.61 inch, 0.64 inch, 0.67 inch, 0.70 inch, 0.73 inch, 0.76 inch, 0.79 inch, 0.82 inch, or 0.85 inch. In some embodiments, the height  4680  of the rear wall  4623  range from 35% to 60%, 35% to 45%, 45% to 68%, 40% to 55%, 30% to 40%, 35% to 45%, 40% to 50%, 45% to 55%, or 50% to 60% of the total height of the golf club head  4400 . For example, the height  4680  of the rear wall  4623  can be 35%, 38%, 41%, 44%, 47%, 50%, 53%, 56%, or 60% of the total height of the golf club head  4400 . 
     The rear wall  4623  of the upper region  4411  can also comprise a height  4680 A. The height  4680 A is measured from the apex  4628  of the top rail  4415  to the inflection point  4686 . The height  4680 A can range from 0.60 inch to 1.0 inch. For example, the height  4680 A can be 0.60 inch, 0.61 inch, 0.64 inch, 0.67 inch, 0.70 inch, 0.73 inch, 0.76 inch, 0.79 inch, 0.82 inch, 0.85 inch, 0.90 inch, 0.95 inch, or 1.0 inch. In some embodiments, the height  4680 A can range from 40% to 75% of the total height of the golf club head  4400 . For example, the height  4680 A can be 40%, 44%, 47%, 50%, 53%, 56%, 60%, 65%, 70%, or 75% of the total height of the golf club head  4400 . 
     The rear wall  4623  of the upper region  4411  further comprises a thickness  4656 . The thickness  4656  is the perpendicular distance of the rear wall  4623  from the outer surface  4403  to the inner surface  4619 . The thickness  4656  of the rear wall  4623  can range from 0.040 inch to 0.080 inch. For example, the thickness  4656  of the rear wall  4623  can be 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.051 inch, 0.054 inch, 0.057 inch, 0.060 inch, 0.063 inch, 0.066 inch, 0.069 inch, 0.071 inch, 0.074 inch, 0.077 inch, or 0.080 inch. In many embodiments, the thickness  4656  of the rear wall  4623  is constant throughout. In other embodiments, the thickness  4656  of the rear wall  4623  can vary. In the exemplary embodiment, the thickness  4656  of the rear wall  4623  is a constant 0.05 inch. The thickness  4656  of the rear wall  4623  allows energy from an impact to transfer to the inflection point  4686  to help induce a buckling effect. 
     The lower region  4413  of the body  4401  comprises a bottom incline  4625 , a lower exterior wall  4627 , a second reference point  4682 , and a third reference point  4620 . The bottom incline  4625  is below and adjacent the inflection point  4686 . The lower exterior wall  4627  is below and adjacent the bottom incline  4625 . The second reference point  4682  is disposed between or positioned at the junction between the bottom incline  4625  and the lower exterior wall  4627 . The third reference point  4620  is disposed between the lower exterior wall  4727  and the sole  4406 . The bottom incline  4625  is angled away from the top rail  4415  and away from the strikeface  4412  in a direction toward the second reference point  4682 . 
     In some embodiments, bottom incline  4625  of the lower region  4413  comprises a bottom incline length  4629 . Bottom incline length  4629  is measured from the inflection point  4686  to the second reference point  4682 . The bottom incline length  4629  can range from 0 inch to 0.45 inch. For example, the bottom incline length  4629  can be 0 inch, 0.05 inch, 0.10 inch, 0.15 inch, 0.20 inch, 0.20 inch, 0.25 inch, 0.30 inch, 0.35 inch, 0.40 inch, or 0.45 inch. In some embodiments, the bottom incline length  4629  can remain constant from the heel region  4402  to the toe region  4404 . In other embodiments, the bottom incline length  4629  can vary from the heel region  4402  to the toe region  4404 . For example, the bottom incline length  4629  can increase from the heel region  4402  to the toe region  4404  as illustrated in  FIG.  44   . In other embodiments, the bottom incline length  4629  can decrease from the heel region  4402  to the toe region  4404 . 
     In some embodiments, the lower region  4413  further comprises a lower angle  4651  measured from between the bottom incline  4625  to the lower exterior wall  4627 . In some embodiments, the lower angle  4651  can be less than 180 degrees. In a number of embodiments, the lower angle  4651  can be 130 degrees to 175 degrees. For example, the lower angle  4651  of the lower region  4413  can be 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, 160 degrees, 165 degrees, 170 degrees, or 175 degrees. 
     The upper region  4411  and the lower region  4413  of the rear  4410  is separated by the inflection point  4686 . Due to the height  4680  of the rear wall  4623 , the inflection point  4686  is positioned low on the body  4401 . In many embodiments, the inflection point  4686  is positioned at least 40% down on the body  4401  below the apex  4628 . For example, the inflection point  4686  can be positioned 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60% down on the body  4401  below the apex  4628 . The low positioned inflection point  4686  allows for more leverage on the upper region  4411  to experience increased bending during impact with a ball, compared to a similar golf club head having a higher inflection point position. 
     The inflection point  4686  comprises an inflection angle  4696  measured from the rear wall  4623  of the upper region  4411 , to the bottom incline  4625  of the lower region  4413 . In some embodiments, the inflection angle  4696  can be measured from the rear wall  4623  to the lower exterior wall  4627  in the absence of the bottom incline  4625  (i.e., the bottom incline length  4629  is 0 inch). The inflection angle  4696  of the inflection point  4686  can range from at least 95 degrees to 150 degrees. In some embodiments, the inflection angle  4696  can be at least 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, or 150 degrees. In some embodiments, the inflection angle  4696  can be consistent from the heel region  4402  to the toe region  4404 . In other embodiments, the inflection angle  4696  can vary from the heel region  4402  to the toe region  4404 . In many embodiments, the inflection angle  4696  allows for inflection point  4686  to act as a buckling point or plastic hinge upon the golf club head  4400  impacting the golf ball at strikeface  4412 . In other examples of a similar golf club head having an inflection angle, wherein the inflection angle is less than 95 degrees (i.e., 90 degrees, or the bottom incline is oriented approximately perpendicular to the strikeface), the inflection angle would impede energy transfer and prevent bending at the inflection point. 
     The inflection point  4686  further comprises a thickness  4660 . The thickness  4660  of the inflection point  4686  is measured perpendicularly of the inflection point  4686  from the exterior surface  4403  to the interior surface  4619 . The thickness  4660  of the inflection point  4686  can range from 0.040 inch, to 0.080 inch. For example, the thickness  4660  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.055 inch, 0.060 inch, 0.65 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. In many embodiments, the thickness  4660  at the inflection point  4686  is constant with the thickness  4656  of the rear wall  4623  and the thickness  4658  of the bottom incline  4625 . In other embodiments, the thickness  4660  at the inflection point  4686  can be less than the thickness  4656  of the rear wall  4623  and the thickness  4658  of the bottom incline  4656 . The thickness  4660  at the inflection point  4686  being consistent with or less than the thickness  4656 ,  4658  of the rear wall  4623  and the bottom incline  4656  allows for more uniform energy transfer and bending. 
       FIG.  34    illustrates another cross-sectional view of the golf club head  4400 , similar to the detailed cross-section of golf club head  4400  illustrated in  FIG.  30   . The body  4401  of golf club head  4400  further comprises a minimum distance  4616 , and a maximum distance  4618 . The minimum distance of the body  4401  is measured as the perpendicular distance from the exterior surface  4403  of the strikeface  4412  in the upper region  4411  to the exterior surface  4403  of the rear wall  4623 . The minimum distance  4616  can range from 0.20 inch to 0.40 inch. For example, the minimum distance  4616  can be 0.20 inch, 0.22 inch, 0.24 inch, 0.26 inch, 0.28 inch, 0.30 inch, 0.32 inch, 0.34 inch, 0.36 inch, 0.038 inch, or 0.40 inch. In some embodiments, the minimum distance  4616  of the body  4401  can be less the bottom incline length  4629 . The maximum distance  4618  of the body  4401  is measured as the perpendicular distance from the exterior surface  4403  of the strikeface  4412  in the lower region  4413  to the exterior surface  4403  of the third reference point  4620 . The maximum distance  4618  can range from 0.60 inch to 0.90 inch. For example, the maximum distance  4618  can be 0.60 inch, 0.64 inch, 0.68 inch, 0.72 inch, 0.76 inch, 0.80 inch, 0.84 inch, 0.88 inch, or 0.90 inch. 
     As illustrated in  FIG.  32 - 34   , the golf club head  4400  can be a hollow, or at least partially hollow body comprising an internal cavity  4416 . Internal cavity  4416  of the body  4401  comprises a volume. The volume of the internal cavity  4416  can range from 0.65 inch 3  (10.65 cm 3 ) to 1.05 inch 3  (17.21 cm 3 ). In some embodiments, the internal cavity  4416  can comprise a volume of 0.65 inch 3  (10.65 cm 3 ), 0.70 inch 3  (11.47 cm 3 ), 0.75 inch 3  (12.29 cm 3 ), 0.80 inch 3  (13.11 cm 3 ), 0.85 inch 3  (13.93 cm 3 ), 0.90 inch 3  (14.75 cm 3 ), 0.95 inch 3  (15.57 cm 3 ), 1.00 inch 3  (16.39 cm 3 ), or 1.05 inch 3  (17.21 cm 3 ). Similarly, the solid portion of the body  4401 , void of the cavity  4416 , further comprises a material volume. The material volume of the body  4401  can range from 2.50 inch 3  (40.97 cm 3 ) to 3.50 inch 3  (57.35 cm 3 ). For example, the material volume of the body  4401  can be 2.50 inch 3  (40.97 cm 3 ), 2.60 inch 3  (42.61 cm 3 ), 2.70 inch 3  (44.25 cm 3 ), 2.80 inch 3  (45.88 cm 3 ), 2.90 inch 3  (47.52 cm 3 ), 3.00 inch 3  (49.16 cm 3 ), 3.10 inch 3  (50.80 cm 3 ), 3.20 inch 3  (52.44 cm 3 ), 3.30 inch 3  (54.08 cm 3 ), 3.40 inch 3  (55.72 cm 3 ), or 3.50 inch 3  (57.35 cm 3 ). 
     In many embodiments, the internal cavity  4416  of the body  4401  can be void of any substance. In other embodiments, the internal cavity  4416  of the body  4401  can comprise a polymer (not pictured), wherein the polymer can be at least partially filling the internal cavity  4416 . The polymer can be polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, polycarbonate, polypropylene, other thermoplastics, composites polymers or any combination thereof. The polymer can fill 10% to 80% 10% to 25%, 15% to 30%, 30% to 45%, 45% to 60%, 60% to 75%, 75% to 80%, 10% to 40%, 30% to 60%, or 40% to 80% of the internal cavity  4416  of the body  4401 . For example, the polymer can fill 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% of the internal cavity  4416  of the body  4401 . In some embodiments, the polymer fills 80% of the internal cavity  4416  of the body  4401 . 
     The polymer to at least partially fill the internal cavity  4416  of the body  4401  comprises a specific gravity ranging from 0.05 to 4. For example, the specific gravity of the polymer can be 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, or 4. In some embodiments, the specific gravity of the polymer is proportional to the mass of the polymer, wherein 1 specific gravity of the polymer is equal to 1 gram. Similarly, in those exemplary embodiments, the volume is proportional to the polymer specific gravity, wherein 1 specific gravity of the polymer is equal to 1 cc. In other embodiments, the volume is not proportional to the specific gravity of the polymer. For example, the ratio of the polymer specific gravity to the polymer volume can be 2:1 cc, 2:3 cc, 2:4 cc, 3:1 cc, 3:2 cc, 3:4 cc, 4:1 cc, 4:2 cc, or 4:3 cc. 
     The mass of the polymer allows for the swing weight of the golf club head  4400  to be customizable for each player. Increasing the volume of the polymer, and thus the mass, increases the swing weight. Similarly, decreasing the volume of the polymer decreases the swing weight. Having the appropriate swing weight for each individual player improves feel during a swing and can improve performance such as swing speed, swing path, ball speed, and ball trajectory. The polymer can further increase the overall mass of the golf club head  4400  more toward the sole  4406 . Increasing the mass more toward the sole shifts the CG low and back, thereby improves the moment of inertia. 
     In some embodiments, the golf club head  4400  can further comprise an aperture (not pictured) located on the toe region  4404 . The aperture comprises internal threads and is configured to receive a threaded screw weight (not pictured). The threaded screw weight comprises a mass, wherein the mass of the threaded screw weight can range from 2 grams to 12 grams. In other embodiments, the mass of the threaded screw weight can range from 4 grams to 10 grams. In some embodiments, the screw weight can be 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, 7 grams, 8 grams, 9 grams, 10 grams, 11 grams, or 12 grams. The mass of the screw weight correlates with the length of the screw weight, wherein a longer threaded screw weight equates to a greater mass. The threaded screw weight further affects the mass and overall swing weight of the golf club head  4400 . Therefore, the threaded screw weight can improve the feel of the golf club head  4400 , as well as performance characteristics (e.g., swing speed, ball speed, and ball flight). 
     In many embodiments, the low positioning of the inflection point  4686  can provide an increase in golf ball speed over golf club head  1200  (or other standard golf club heads), can reduce the spin rate of standard hybrid club heads (or other standard golf club heads), and can increase the launch angle over both the standard hybrid and iron club heads. An inflection point positioned less than 40% down the body from the apex cannot buckle as easily because the high positioning decreases the leverage for the upper region to bend. Therefore, when the golf ball impacts strikeface  4412  of the club head  4400  with inflection point  4686  positioned at least 40% down the body  4401  from the apex  4628 , the strikeface  4412  springs back like a drum, and the rear  4410  bends in a controlled buckle manner more than a golf club head having an inflection point positioned less than 40% down the body from the apex. 
     A standard top rail, and rear wall without a low positioned inflection point does not have this hinge/buckling effect, nor does it absorb a high level of stress over a large volumetric area of the top rail and rear wall. Therefore, the standard strikeface does not contract and then recoil as much as strikeface  4412 . By adding more spring to the back end of the club (due to the thinness of the top rail  4415  and rear wall  4623 , and the low position of the inflection point  4686 ), more force is displaced throughout the volume of the structure. The stress is observed over a greater area of strikeface  4412 , top rail  4415 , and rear wall  4623  of the golf club head  4400 . Peak stresses can be seen in the typically just along the top rail in a standard club head. However, more peak stresses are seen in the golf club head  4400  but distributed over a large volume of the material. The hinge and bend regions of the golf club head  4400  (i.e., the inflection point  4686 ) will not deform as long as the stress does not meet the critical buckling threshold. Inflection point  4686  and its placement can be designed to be under the critical K value of the buckling threshold. 
     Further, upon impact with the golf ball, strikeface  4412  can bend inward at a greater distance than on a golf club without a thin top rail  4415 , a thin rear wall  4623 , and an inflection point  4686  positioned at least 40% down the body from the apex  4628 . In some embodiments, the strikeface  4412  has a 10% to a 50% greater deflection than a strikeface on a golf club head without a thin top rail, a thin rear wall, and a low positioned inflection point. For example, the strikeface  4412  can have a 10%, a 15%, a 20%, a 30%, a 35%, a 40%, a 45%, or a 50% greater deflection than a strikeface of a golf club head without a thin top rail  4415 , thin rear wall  4623 , and low positioned inflection point  4686 . 
     As shown in  FIG.  34   , a further deflection feature of the golf club head  4400  can be the uniform thinned region  4860 , located at the sole  4406  and stretching between the rear  4410  of the body  4401  and the strikeface  4412 , toward a cascading sole portion of the sole (as described in greater detail below). The uniform thinned region  4860  can provide multiple benefits. First, the uniform thinned region  4860  can reduce stress on the strikeface  4412  caused during impact with the golf ball. Second, the uniform thinned region  4860  can bend allowing the strikeface  4412  to experience greater deflection. Third, the uniform thinned region  4860  removes weight from the sole area, allowing the weight to be redistributed more toward the rear of the golf club head  4400 . At impact, the energy imparted to the strikeface  4412  by the golf ball can cause the uniform thinned region  4860  to bend outward, which in turn increases the strikeface  4412  deflection. After bending, the uniform thinned region  4860  rebounds back to its original position returning the majority of the energy from impact back to the golf ball. The result is the golf club head  4400  imparts increased ball speeds and greater travel distances to the golf ball after impact. 
     In some embodiments, body  4401  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, body  4401  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, strikeface  4412  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, strikeface  4412  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, body  4401  can comprise the same material as strikeface  4412 . In some embodiments, body  4401  can comprise a different material than strikeface  4412 . 
       FIG.  35    illustrates a back perspective view of an embodiment of a golf club head  4900 , and  FIG.  36    illustrates a back heel-side perspective view of the golf club head  4900  according to the embodiment of  FIG.  35   . In some embodiments, the golf club head  4900  can be similar to golf club head  1000  ( FIG.  1   ), golf club head  2200  ( FIG.  8   ), golf club head  2700  ( FIG.  13   ), golf club head  3200  ( FIG.  18   ), golf club head  3700  ( FIG.  23   ), and/or golf club head  4400  ( FIG.  30   ). The golf club head  4900  can be an iron-type golf club head. In some embodiments, the golf club head  4900  does not comprise a badge or a custom tuning port. 
     The golf club head  4900  comprises a body  4901 . In some embodiments, the body  4901  can be similar to body  1001  ( FIG.  1   ), body  2201  ( FIG.  8   ), body  2701  ( FIG.  13   ), body  3201  ( FIG.  18   ), body  3701  ( FIG.  23   ), and/or body  4401  ( FIG.  30   ). The body  4901  further comprises an exterior surface  4903 , a strikeface  4912 , a heel region  4902 , a toe region  4904  opposite the heel region, a sole  4906 , a top rail  4915 , and a rear  4910 . 
     The body  4901  of  FIGS.  49 - 52    further comprises a blade length. The blade length for the body  4901  can be measured similar to blade length  3725  as shown and described for golf club head  3700  in  FIG.  43    (i.e., a measurement parallel to the flat surface of the strikeface, from a toe edge of the strikeface, to strikeface end before the strikeface integrally curves into the hosel). The blade length of the body  4901  can range from 2.50 inches (6.35 cm) to 2.90 inches (7.37 cm). In some embodiments, the blade length can range from 2.50 inches (6.35 cm) to 2.60 inches (6.60 cm), 2.60 inches (6.60 cm) to 2.70 inches (6.86 inches), 2.70 inches (6.86 cm) to 2.80 inches (7.11 cm), or 2.80 inches (7.11 cm) to 2.90 inches (7.37 cm). For example, in some embodiments, the body  4901  can comprise a blade length of 2.50 inches (6.35 cm), 2.54 inches (6.45 cm), 2.58 inches (6.55 cm), 2.62 inches (6.65 cm), 2.66 inches (6.76 cm), 2.70 inches (6.86 cm), 2.74 inches (6.96 cm), 2.78 inches (7.06 cm), 2.82 inches (7.16 cm), 2.86 inches (7.264 cm), or 2.90 inches (7.37 cm). 
     As shown in  FIG.  39   , a further deflection feature of the golf club head  4900  can be the uniform thinned region  5360 , located at the sole  4906  and stretching between the rear  4910  of the body  4901  and the strikeface  4912 , toward a cascading sole portion of the sole (as described in greater detail below). In the illustrated embodiment, the uniform thinned region  5360  comprises a sole thickness  5361  measured perpendicular from the exterior surface  4903  to an interior surface  5119  at the uniform thinned region  5360 , which can remain constant from the bottom of the strikeface  4912  to adjacent the cascading sole portion of the sole  4906 . In some embodiments, the sole thickness  5361  of the uniform thinned region  5360  can be thinner than a conventional sole. For example, in some embodiments, the sole thickness  5361  of the uniform thinned region  5360  may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness  5361  of the uniform thinned region  5360  may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness of the uniformed thinned region  5360  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
       FIG.  37    illustrates a cross-section of the golf club head  4900 , according to one embodiment. As seen in  FIG.  37   , the strikeface  4912  comprises a high region  5176 , a middle region  5174 , and a low region  5172 . 
     The strikeface  4912  of the body  4901  further comprises a thickness  5154  measured perpendicular to the strikeface  4912  from the exterior surface  4903  to an interior surface  5119 . The thickness  5154  of the strikeface  4912  can range from 0.040 inch to 0.200 inch. In some embodiments, the thickness  5154  of the strikeface  4912  can range from 0.040 inch to 0.080 inch, 0.080 inch to 0.120 inch, 0.120 inch to 0.160 inch, or 0.160 inch to 0.20 inch. For example, the thickness  5154  of the strikeface  4912  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.055 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, 0.080 inch, 0.085 inch, 0.090 inch, 0.095 inch, 0.100 inch, 0.150 inch, or 0.200 inch. In some embodiments, the thickness  5154  of the strikeface  4912  can vary from the heel region  4902  to the toe region  4904 , and/or from the top rail  4915  to the sole  4906 . For example, the thickness  5154  of the strikeface  4912  can be greatest at the central portion near the middle region  5174  of the strikeface  4912 , and taper along the periphery near the high region  5176  and the low region  5172  of strikeface  4912 . In many embodiments, the center of the strikeface  4912  can have a thickness  5154  range of 0.10 inch to 0.14 inch, and the periphery of the strikeface  4912  can have a thickness  5154  range of 0.06 inch to 0.10 inch. In some embodiments, the center of the strikeface  4912  can have a thickness  5154  range of 0.10 inch to 0.12 inch, or 0.12 inch to 0.14 inch. In other embodiments, the periphery of the strikeface  4912  can have a thickness  5154  range of 0.06 inch to 0.08 inch, or 0.08 inch to 0.10 inch. In other examples, the thickness  5154  can increase, decrease, or any variation thereof starting at the central region near the middle region of the strikeface and extending toward the periphery near the high region  5176  and the low region  5172 . 
     The cross-section of the golf club head in  FIG.  37    further illustrates the rear  4910 . The rear  4910  can comprise an upper region  4911 , a lower region  4913 , and an inflection point  5186  disposed between the upper region  4911  and the lower region  4913 . The inflection point  5186  is further located at the junction between the rear wall  5123  and the bottom incline  5125 . The inflection point  5186  is located nearer to the sole  4906  of the club head  4900  than the top rail  4915 . 
     The upper region  4911  of rear  4910  comprises a top rail  4915 , an apex of top rail  5128 , a rear wall  5123  orientated parallel to the strikeface  4912 , and a first reference point  5122  disposed between the top rail  4915  and the rear wall  5123 . The first reference point  5122  is located at the junction between the top rail  4915  and the rear wall  5123  parallel to the strikeface. In many embodiments, the rear wall  5123  of the upper region  4911  is located below and adjacent the top rail  4915 . 
     In some embodiments, top rail  4915  of the upper region  4911  can be a flatter and taller top rail or skirt than in irons known to one skilled in the art. The flatter and taller rail can compensate for mishits or strikeface  4912  to increase playability off the tee. In some embodiments. The length of top rail  4915 , measured from heel region  4902  to toe region  4904 , can be 60% to 95% of the length of the golf club head  4900 . 
     The top rail  4915  of the upper region  4911  comprises a thickness  5152 . The thickness  5152  of the top rail  4915  can range from 0.040 inch to 0.080 inch. In some embodiments, the thickness  5152  of the top rail  4915  can range from 0.040 inch to 0.060 inch, or 0.060 inch to 0.080 inch. For example, the thickness  5152  of the top rail  4915  can be 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.051 inch, 0.054 inch, 0.057 inch, 0.060 inch, 0.063 inch, 0.066 inch, 0.069 inch, 0.071 inch, 0.074 inch, 0.077 inch, or 0.080 inch. In many embodiments, the thickness  5152  of the top rail  4915  is constant throughout. In other embodiments, the thickness  5152  of the top rail  4915  can vary. In the exemplary embodiment, the thickness  5152  of the top rail  4915  decreases from the strikeface  4912  toward the rear wall  5123 . In many embodiments, due to the thickness of the top rail, top rail can provide an increase in the overall bending of strikeface. In some embodiments, the bending of strikeface can allow for a 2% to 5% increase of energy. 
       FIG.  38    illustrates the top rail  4915  and a portion of the rear  4910  of the cross-section of the golf club head of  FIG.  35   , different from cross-section of golf club head  1200  as shown in  FIG.  4   . The strikeface  4912  further comprises a strikeface angle  5250 . The strikeface angle  5250  is measured from the strikeface  4912  to the top rail  4915 , wherein the strikeface angle  5250  can range from 70 degrees to 160 degrees or 70 degrees to 110 degrees. In some embodiments, strikeface angle can be 70 degrees, 75 degrees, 80 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, or 160 degrees. 
       FIG.  38    further illustrates the top rail  4915  comprising a top rail angle  5245 . The top rail angle  5245  is measured from rear wall  5123  to the top rail  4915 . In many embodiments, the top rail angle  5245  can range from 35 degrees to 150 degrees or 70 degrees to 145 degrees. In some embodiments, top rail angle  5245  can be 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, or 150 degrees. 
     The rear wall  5123  of the upper region  4911  comprises a height  5180 . The height  5180  of the rear wall  5123  is measured from the first reference point  5122  to the inflection point  5186 , wherein the first reference point  5122  is positioned at the junction between the top rail  4915  and the rear wall  5123  parallel to the strikeface  4912 . The height  5180  of the rear wall  5123  can range from 0.55 inch to 0.60 inch, 0.60 inch to 0.70 inch, 0.70 inch to 0.80 inch, 0.80 inch to 0.85, 0.85 inch to 0.90 inch, 0.90 inch to 0.95, 0.95 inch to 1 inch or 0.55 inch to 1 inch. For example, the height  5180  of the rear wall  5123  can be 0.55 inch, 0.58 inch, 0.61 inch, 0.64 inch, 0.67 inch, 0.70 inch, 0.73 inch, 0.76 inch, 0.79 inch, 0.82 inch, 0.85 inch, 0.88 inch, 0.91 inch, 0.94 inch, 0.97 inch, or 1 inch. In some embodiments, the height  5180  of the rear wall  5123  range from 35% to 60%, 35% to 45%, 45% to 68%, 40% to 55%, 30% to 40%, 35% to 45%, 40% to 50%, 45% to 55%, or 50% to 60% of the total height of the golf club head  4900 . For example, the height  5180  of the rear wall  5123  can be 35%, 38%, 41%, 44%, 47%, 50%, 53%, 56%, or 60% of the total height of the golf club head  4900 . 
     The rear wall  5123  of the upper region  4911  can also comprise a secondary height  5180 A. The secondary height  5180 A is measured from the apex  5128  of the top rail  4915  to the inflection point  5186 . The secondary height  5180 A can range from 0.60 inch to 1.2 inch. In some embodiments, the secondary height  5180 A can range from 0.60 inch to 0.80 inch, 0.80 inch to 1.0 inch, or 1.0 inch to 1.20 inches. For example, the secondary height  5180 A can be 0.60 inch, 0.61 inch, 0.64 inch, 0.67 inch, 0.70 inch, 0.73 inch, 0.76 inch, 0.79 inch, 0.82 inch, 0.85 inch, 0.90 inch, 0.95 inch, 1.0 inch, or 1.2 inches. In some embodiments, the secondary height  5180 A can range from 40% to 75% of the total height of the golf club head  4900 . For example, the secondary height  5180 A can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 60%, 65%, 70%, or 75% of the total height of the golf club head  4900 . 
     The rear wall  5123  of the upper region  4911  further comprises a thickness  5156 . The thickness  5156  is the perpendicular distance of the rear wall  5123  from the outer surface  4903  to the inner surface  5119 . The thickness  5156  of the rear wall  5123  can range from 0.040 inch to 0.080 inch. In some embodiments, the thickness  5156  of the rear wall  5123  can range from 0.040 inch to 0.060 inch, or 0.060 inch to 0.080 inch. For example, the thickness  5156  of the rear wall  5123  can be 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.051 inch, 0.054 inch, 0.057 inch, 0.060 inch, 0.063 inch, 0.066 inch, 0.069 inch, 0.071 inch, 0.074 inch, 0.077 inch, or 0.080 inch. In many embodiments, the thickness  5156  of the rear wall  5123  is constant throughout. In other embodiments, the thickness  5156  of the rear wall  5123  can vary. In the exemplary embodiment, the thickness  5156  of the rear wall  5123  is a constant 0.045 inch. The thickness of the rear wall allows energy from an impact to transfer to the inflection point to help induce a buckling effect. 
     The lower region  4913  of the body  4901  comprises a bottom incline  5125 , a lower exterior wall  5127 , a second reference point  5182 , and a third reference point  5120 . The bottom incline  5125  is below and adjacent the inflection point  5186 . The lower exterior wall  5127  is below and adjacent the bottom incline  5125 . The second reference point  5182  is disposed between or positioned at the junction between the bottom incline  5125  and the lower exterior wall  5127 . The third reference point  5120  is disposed between the lower exterior wall  5127  and the sole  4906 . The bottom incline  5125  is angled away from the top rail  4915  and away from the strikeface  4912  in a direction toward the second reference point  5182 . 
     In some embodiments, bottom incline  5125  of the lower region  4913  comprises a bottom incline length  5129 . Bottom incline length  5129  is measured from the inflection point  5186  to the second reference point  5182 . The bottom incline length  5129  can range from 0 inch to 0.55 inch. In some embodiments, the bottom incline length  5129  can range from 0 inch to 0.35 inch, or 0.35 inch to 0.55 inch. For example, the bottom incline length  5129  can be 0 inch, 0.05 inch, 0.10 inch, 0.15 inch, 0.20 inch, 0.20 inch, 0.25 inch, 0.30 inch, 0.35 inch, 0.40 inch, 0.45 inch, 0.50 inch, or 0.55 inch. In some embodiments, the bottom incline length  5129  can remain constant from the heel region  4902  to the toe region  4904 . In other embodiments, the bottom incline length  5129  can vary from the heel region  4902  to the toe region  4904 , as illustrated in  FIG.  35   . For example, the bottom incline length  5129  can increase from the heel region  4902  to the toe region  4904 . In other embodiments, the bottom incline length  5129  can decrease from the heel region  4902  to the toe region  4904 . 
     In some embodiments, the lower region  4913  further comprises a lower angle  5151  measured from between the bottom incline  5125  to the lower exterior wall  5127 . In some embodiments, the lower angle  5151  can be less than 180 degrees. In a number of embodiments, the lower angle  5151  can be 130 degrees to 175 degrees. For example, the lower angle  5151  of the lower region  4913  can be 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, 160 degrees, 165 degrees, 170 degrees, or 175 degrees. 
     The upper region  4911  and the lower region  4913  of the rear  4910  is separated by the inflection point  5186 . Due to the height of the rear wall, the inflection point  5186  is positioned low on the body  4901 . In many embodiments, the inflection point  5186  is positioned at least 40% down on the body  4901  below the apex  5128 . For example, the inflection point  5186  can be positioned 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60% down on the body  4901  below the apex  5128 . The low positioned inflection point  5186  allows for more leverage on the upper region  4911  to experience increased bending during impact with a ball, compared to a similar golf club head having a higher inflection point position. 
     The inflection point  5186  comprises an inflection angle  5196  measured from the rear wall  5123  of the upper region  4911 , to the bottom incline  5125  of the lower region  4913 . In some embodiments, the inflection angle  5196  can be measured from the rear wall  5123  to the lower exterior wall  5127  in the absence of the bottom incline  5125  (i.e., the bottom incline length is 0 inch). The inflection angle  5196  of the inflection point  5186  can range from at least 95 degrees to 150 degrees. In some embodiments, the inflection angle  5196  can be at least 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, or 150 degrees. In some embodiments, the inflection angle  5196  can be consistent from the heel region  4902  to the toe region  4904 . In other embodiments, the inflection angle  5196  can vary from the heel region  4902  to the toe region  4904 . In many embodiments, the inflection angle  5196  allows for the inflection point  5186  to act as a buckling point or plastic hinge upon the golf club head  4900  impacting the golf ball at strikeface  4912 . In other examples of a similar golf club head having an inflection angle, wherein the inflection angle is less than 95 degrees (i.e., 90 degrees, or the bottom incline in oriented approximately perpendicular to the strikeface), the inflection angle would impede energy transfer and prevent bending at the inflection point. 
     The rear wall at the inflection point  5186  further comprises a thickness  5160 . The thickness  5160  at the inflection point  5186  is measured perpendicularly of the inflection point  5186  from the exterior surface  4903  to the interior surface  5119 . The thickness  5160  of the inflection point  5186  can range from 0.040 inch to 0.080 inch. In some embodiments, the thickness  5160  of the inflection point  5186  can range from 0.040 inch to 0.060 inch, or 0.060 inch to 0.080 inch. For example, the thickness  5160  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.055 inch, 0.060 inch, 0.65 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. In many embodiments, the thickness  5160  of the inflection point  5186  is constant with the thickness  5156  of the rear wall  5123  and the thickness  5158  of the bottom incline  5125 . In other embodiments, the thickness  5160  of the inflection point  5186  can be less than the thickness  5156  of the rear wall  5123  and the thickness  5158  of the bottom incline  5125 . The thickness  5160  of the inflection point  5186  being consistent with or less than the thickness  5156 ,  5158  of the rear wall  5123  and the bottom incline  5125  allows for more uniform energy transfer and bending. 
     The body  4901  of the golf club head  4900  further comprises a minimum distance  5116 , and a maximum distance  5118 . The minimum distance  5116  of the body  4901  is measured as the perpendicular distance from the exterior surface  4903  of the strikeface  4912  in the upper region  4911  to the exterior surface  4903  of the rear wall  5123 . The minimum distance  5116  can range from 0.20 inch to 0.44 inch. In some embodiments, the minimum distance  5116  can range from 0.20 inch to 0.30 inch, or 0.30 inch to 0.44 inch For example, the minimum distance  5116  can be 0.20 inch, 0.22 inch, 0.24 inch, 0.26 inch, 0.28 inch, 0.30 inch, 0.32 inch, 0.34 inch, 0.36 inch, 0.38 inch, 0.40 inch, 0.42 inch, or 0.44 inch. The maximum distance  5118  of the body  4901  is measured as the perpendicular distance from the exterior surface  4903  of the strikeface  4912  in the lower region  4913  to the exterior surface  4903  of the third reference point  5120 . The maximum distance  5118  can range from 0.60 inch to 1.0 inch. In some embodiments, the maximum distance  5118  can range from 0.60 inch to 0.80 inch, or 0.80 inch to 1.0 inch. For example, the maximum distance  5118  can be 0.60 inch, 0.64 inch, 0.68 inch, 0.72 inch, 0.76 inch, 0.80 inch, 0.84 inch, 0.88 inch, 0.90 inch, 0.92 inch, 0.94 inch, 0.96 inch, or 1.0 inch. 
     The body  4901  of the golf club head  4900  further comprises an internal cavity distance  5114  as illustrated in  FIG.  39   . The internal cavity distance  5114  is measured as the perpendicular distance from the exterior surface  4903  of the strikeface  4912  in the lower region  4913  to the interior surface  5119  of the rear wall  5123 . The internal cavity distance  5114  can range from 0.40 inch to 0.80 inch. In some embodiments, the internal cavity distance  5114  can range from 0.40 inch to 0.60 inch, or 0.60 inch to 0.80 inch. For example, the internal cavity distance  5114  can be 0.40 inch, 0.44 inch, 0.48 inch, 0.52 inch, 0.56 inch, 0.60 inch, 0.64 inch, 0.68 inch, 0.72 inch, 0.76 inch, or 0.80 inch. 
     As illustrated in  FIG.  35 - 38   , the golf club head  4900  can be a hollow, or at least partially hollow body comprising an internal cavity  4916 . Internal cavity  4916  of the body  4901  comprises a volume. The volume of the internal cavity  4916  can range from 1.20 inch 3  (19.66 cm 3 ) to 2.0 inch 3  (32.77 cm 3 ). In some embodiments, the internal cavity  4916  can range from 1.20 inch 3  (19.66 cm 3 ) to 1.6 inch 3  (26.22 cm 3 ), or 1.6 inch 3  (26.22 cm 3 ) to 2.0 inch 3  (32.77 cm 3 ). For example, the internal cavity  4916  can comprise a volume of 1.20 inch 3  (19.66 cm 3 ), 1.30 inch 3  (21.30 cm 3 ), 1.40 inch 3  (22.94 cm 3 ), 1.50 inch 3  (24.58 cm 3 ), 1.60 inch 3  (26.22 cm 3 ), 1.70 inch 3  (27.86 cm 3 ), 1.80 inch 3  (29.50 cm 3 ), 1.90 inch 3  (31.14 cm 3 ), or 2.0 inch 3  (32.77 cm 3 ). Similarly, the solid portion of the body  4900 , void of the cavity  4916 , further comprises a material volume. The material volume of the body can range from 3.0 inch 3  (49.16 cm 3 ) to 4.0 inch 3  (65.55 cm 3 ). In some embodiments, the material volume of the body can range from 3.0 inch 3  (49.16 cm 3 ) to 3.5 inch 3  (57.35 cm 3 ), or 3.5 inch 3  (57.35 cm 3 ) to 4.0 inch 3  (65.55 cm 3 ). For example, the material volume of the body can be 3.0 inch 3  (40.97 cm 3 ), 3.10 inch 3  (50.80 cm 3 ), 3.20 inch 3  (52.44 cm 3 ), 3.30 inch 3  (54.08 cm 3 ), 3.40 inch 3  (55.72 cm 3 ), 3.50 inch 3  (57.35 cm 3 ), 3.60 inch 3  (58.99 cm 3 ), 3.70 inch 3  (60.63 cm 3 ), 3.80 inch 3  (62.27 cm 3 ), 3.90 inch 3  (63.91 cm 3 ), or 4.0 inch 3  (65.55 cm 3 ). 
     In many embodiments, the internal cavity  4916  of the body  4900  can be void of any substance. In other embodiments, the internal cavity  4916  of the body  4900  can comprise a polymer (not pictured), wherein the polymer can at least partially fill the internal cavity  4916 . The polymer can be polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, polycarbonate, polypropylene, other thermoplastics, composites polymers or any combination thereof. The polymer can fill 10% to 80%, 10% to 25%, 15% to 30%, 30% to 45%, 45% to 60%, 60% to 75%, 75% to 80%, 10% to 40%, 30% to 60%, or 40% to 80% of the internal cavity of the body. For example, the polymer can fill 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% of the internal cavity of the body. In some embodiments, the polymer fills 80% of the internal cavity  4916  of the body  4901 . 
     The polymer to at least partially fill the internal cavity  4916  of the body  4901  comprises a specific gravity ranging from 0.05 to 4. In some embodiments, the specific gravity ranges from 0.05 to 0.10, 0.10 to 0.50, 0.50 to 1.0, 1.0 to 2.0, or 2.0 to 4.0. For example, the specific gravity of the polymer can be 0.50, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, or 4.0. In some embodiments, the specific gravity of the polymer is proportional to the mass of the polymer, wherein 1 specific gravity of the polymer is equal to 1 gram. Similarly, in those exemplary embodiments, the volume is proportional to the polymer specific gravity, wherein 1 specific gravity of the polymer is equal to 1 cc. In other embodiments, the volume is not proportional to the specific gravity of the polymer. For example, the ratio of the polymer specific gravity to the polymer volume can be 2:1 cc, 2:3 cc, 2:4 cc, 3:1 cc, 3:2 cc, 3:4 cc, 4:1 cc, 4:2 cc, or 4:3 cc. 
     In some embodiments, as illustrated in  FIG.  40   , the golf club head  4900  can further comprise a first aperture  5134  located on the toe region  4904  and a second aperture  5136  located in a hosel of the golf club head  4900 . The first aperture  5134  is configured to receive a toe weight (not pictured), wherein the toe weight can range from 2 grams to 7 grams. In some embodiments, the toe weight can range from 2 grams to 5 grams, or 5 grams to 7 grams. For example, the toe weight can be 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, or 7 grams. The second aperture  5136  is configured to receive a tip weight (not pictured), wherein the tip weight can range from 2 grams to 7 grams. In some embodiments, the tip weight can range from 2 grams to 5 grams, or 5 grams to 7 grams. For example, the tip weight can be 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, or 7 grams. In many embodiments, the first aperture  5134  and the second aperture  5136  can further be configured to receive the polymer. The first aperture  5134  can receive 1 gram to 9 grams of polymer (e.g., 1 gram, 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, 7 grams, 8 grams, or 9 grams). Similarly, the second aperture  5136  can receive 1 gram to 9 grams of polymer (e.g., 1 gram, 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, 7 grams, 8 grams, or 9 grams). The toe and tip weight, and the polymer housed within the first aperture  5134  and the second aperture  5136  can affect the swing weight to optimize CG and MOI. 
     The internal cavity  4916  of the body  4901  further comprises interior surface  5119 . In some embodiments, the interior surface  5119  of the rear  4910  is a planar and smooth surface. In other embodiments as illustrated in  FIG.  38   , the interior surface  5119  of the internal cavity  4916  of the rear  4910  comprises a plurality of ribs  4952 . The plurality of ribs  4952  extend in a direction from top rail  4915  toward the sole  4906 . The plurality of ribs  4952  can be located anywhere on interior surface  5119  of the rear  4910 . In some examples, the plurality of ribs  4952  can be positioned onto a portion of interior surface  5119  of the lower exterior wall  5127 . In other examples, the plurality of ribs  4952  can be positioned on a portion of the interior surface  5119  of the rear wall  5123 . In some embodiments, the plurality of ribs  4952  can be positioned on a portion of the interior surface  5119  of the rear  4910  and can extend into another portion of the rear  4910 . For example, the plurality of ribs  4952  are positioned on a portion of the interior surface  5119  of the rear wall  5123  and can extend up to at least a portion of the bottom incline  5125 , or at least a portion of the lower exterior wall  5127 . The plurality of ribs  4952  can comprise between one to eight ribs. For example, the plurality of ribs  4952  can comprise one rib, two ribs, three ribs, four ribs, five ribs, six ribs, seven ribs, or eight ribs. In embodiments having one or more plurality of ribs  4952 , the plurality of ribs  4952  can be spaced equidistance from each other or more concentrated near the heel region  4902 , toe region  4904 , top rail  4915 , or sole  4906 . The plurality of ribs  4952  and the location of the plurality of ribs  4952  can help optimize the frequency and amplitude of sound response. 
     In some embodiments, body  4901  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, body  4901  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, strikeface  4912  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, strikeface  4912  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, the body  4901  can comprise the same material as the strikeface  4912 . In some embodiments, the body  4901  can comprise a different material than the strikeface  4912 . 
       FIG.  42    illustrates a back perspective view of an embodiment of golf club head  5600  and  FIG.  43    illustrates a back heel-side perspective view of golf club head  5600  according to the embodiment of  FIG.  42   . In some embodiments, golf club head  5600  can be similar to golf club head  1000  ( FIG.  1   ), golf club head  2200  ( FIG.  8   ), golf club head  2700  ( FIG.  13   ), golf club head  3200  ( FIG.  18   ), golf club head  3700  ( FIG.  23   ), and/or golf club head  4400  ( FIG.  30   ). Golf club head  5600  can be an iron-type golf club head. 
     Golf club head  5600  comprises a body  5601 . In some embodiments, body  5601  can be similar to body  1001  ( FIG.  1   ), body  2201  ( FIG.  8   ), body  2701  ( FIG.  13   ), body  3201  ( FIG.  18   ), body  3701  ( FIG.  23   ), and/or body  4401  ( FIG.  30   ). The body  5601  comprises an exterior surface  5603 , a strikeface  5612 , a heel region  5602 , a toe region  5604  opposite the heel region  5602 , a sole  5606 , a top rail  5615 , and a rear  5610 . The strikeface  5612 , sole  5606 , top rail  5615 , and rear  5610  of the body  5601  together form an internal cavity  5616 . Furthermore, the golf club head  5600  can be divided into an upper region  5611  and a lower region  5613  (see  FIG.  44   ). 
     The rear  5610  of the golf club head  5600  can comprise an indention  5630  that alters the deflection and/or weighting of the club head. The rear  5610  of the golf club head can further comprise a ledge  5825  or step wall below the indention  5630 . The rear  5610  further comprises an upper perimeter portion  5609 , which extends along the top rail  5615  and wraps down the sides of the toe region  5604  and heel region  5602 . A toe slit  5666  and a heel slit  5662  are each positioned between a part of the upper perimeter portion  5609  and a lower exterior wall  5727  of a lower region  5613  of the club head  5600 , allowing structural bending between upper and lower halves of the club head  5600 . This bending allowed by the toe slit  5666  and heel slit  5662  results in greater deflection of the strikeface  5612  over a club head without these slits. The club head  5600  can further comprise a vibration damping layer  5878  on an interior surface  5819  of the strikeface  5612 . In some embodiments, the internal cavity  5616  can be filled or partially filled with a polymer material. 
     Body  5601  of  FIGS.  42 - 48    comprises a blade length. The blade length for body  5601  can be measured similar to blade length  3725  as shown and described in  FIG.  29    (i.e., a measurement parallel to the flat surface of the strikeface  3712 , from a toe edge  3726  of the strikeface  3712 , to strikeface end  3727  before the strikeface  3712  integrally curves into the hosel). The blade length of the body  5601  can range from 2.50 inches (6.35 cm) to 2.90 inches (7.37 cm). For example, in some embodiments, the body  3701  can comprise a blade length of 2.50 inch (6.35 cm), 2.54 inch (6.45 cm), 2.58 inch (6.55 cm), 2.62 inch (6.65 cm), 2.66 inch (6.76 cm), 2.70 inch (6.86 cm), 2.74 inch (6.96 cm), 2.78 inch (7.06 cm), 2.82 inch (7.16 cm), 2.86 inch (7.264 cm), or 2.90 inch (7.37 cm). 
     The sole can comprise a cascading sole portion of the sole, as described in greater detail below. As shown in  FIG.  46   , a deflection feature of the golf club head  5600  can be a uniform thinned region  6060 , located at the sole  5606  and stretching between the rear  5610  of the body  5601  and the strikeface  5612 , toward the cascading sole portion of the sole. In the illustrated embodiment, the uniform thinned region  6060  comprises a sole thickness measured perpendicular from the exterior surface  5603  to an interior surface  5819  at the uniform thinned region  6060 , which can remain constant from the bottom of the strikeface  5612  to adjacent the cascading sole portion of the sole. In some embodiments, the sole thickness of the uniform thinned region  6060  can be thinner than a conventional sole. For example, in some embodiments, the sole thickness of the uniform thinned region  6060  may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness of the uniform thinned region  6060  may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness of the uniformed thinned region  4860  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
       FIG.  44    illustrates a cross-section of golf club head  5600  along the cross-sectional line LVIII-LVIII in  FIG.  42   , according to one embodiment. As seen in  FIG.  44   , strikeface  5612  comprises a high region  5876 , a middle region  5874 , and a low region  5872 . 
     The strikeface  5612  of the body  5601  further comprises a thickness  5854  measured perpendicularly to the strikeface  5612  from the exterior surface  5603  to an interior surface  5819 . The thickness  5854  of the strikeface  5612  can range from 0.040 inch to 0.100 inch. For example, the thickness  5854  of the strikeface  4412  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.055 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, 0.080 inch, 0.085 inch, 0.090 inch, 0.095 inch, or 0.100 inch. In some embodiments, thickness  5854  of the strikeface  5612  can vary from the heel region  5602  to the toe region  5604 , and/or from the top rail  5615  to the sole  5606 . For example, the thickness  5854  of the strikeface  5612  can be greatest at the central portion near the middle region  5874  of the strikeface  5612 , and taper along the periphery near the high region  5876  and the low region  5872  of strikeface  5612 . In many embodiments, the center of the strikeface  5612  can have a thickness  5854  of 0.090 inch and the periphery of the strikeface  5612  can have a thickness  5854  of 0.070 inch. In other examples, the thickness  5854  can increase, decrease, or any variation thereof starting at the central region near the middle region  5874  of the strikeface  5612  and extending toward the periphery near the high region  5876  and the low region  5872 . 
     The upper region  5611  of rear  5610  comprises the upper perimeter portion  5609 , the indention  5630 , and the ledge  5825 . The upper perimeter portion comprises the top rail of the club head and wraps down around a length of the toe and heel regions of the club head. The upper perimeter portion  5609  extends along a top edge of the golf club head  5600  from the heel region  5602  to the toe region  5604 . In the toe region  5604  the upper perimeter portion  5609  extends down along a perimeter of the toe region  5604 . In some embodiments, the upper perimeter portion  5609  extends roughly halfway down along the perimeter of the toe region  5604 . The upper perimeter portion abuts the indention. The upper perimeter portion  5609  of the rear  5610  can provide perimeter weighting for the club head  5600 . In addition, the upper perimeter portion  5609  allows stresses in the top rail  5615  to be dissipated into the rear  5610  of the club head  5600 . 
     The indention  5630  is located on the exterior surface  5603 , below the upper perimeter portion and above the lower region  5613  of the club head  5600 . The indention  5630  of the rear  5610  extends inwards towards the strikeface of the golf club head  5600 . The indention  5630  is located in the upper portion  5611  of the club head  5600 . In some embodiments, the indention  5630  is located primarily in an upper half of the golf club head  5600 . The indention  5630  is bounded on its top, toe, and heel sides by the upper perimeter portion  5609 . The indention  5630  is bounded on its bottom side by the ledge  5825 . 
     The ledge  5825  extends in a direction generally from the heel region  5602  towards the toe region  5604 . The ledge  5825  helps form a lower boundary of the indention  5630 . The ledge  5825  can be located at various heights above the ground plane  10  when the club head  5600  is at address position. The ledge  5825  can comprise multiple segments, wherein each segment is located at a different height above the ground plane  10 , as shown in the rear view of  FIG.  42   . For example, the ledge  5825  can comprise a segment located in the toe region  5604  that is higher from the ground plane  10  than a segment located, at least partially, in the heel region  5602 . 
     The ledge  5825  of the rear  5610  of the club head  5600  can be positioned in a plane roughly perpendicular to the strikeface  5612  plane. The ledge  5825  runs the length of the club head  5600  from the heel region  5602  to the toe region  5604 . The ledge  5825  can also be thought of as a ledge or groove. At the heel end the ledge  5825  can blend into the heel slit  5662 . At the toe end, the ledge  5825  can blend into the toe slit  5666 . 
     The ledge  5825  can be angled with respect to the ground plane  10  at a ledge angle (not illustrated). In some embodiments, the ledge angle, measured from the ledge  5825  to ground plane  10 , can range from 15 degrees to 45 degrees. In some embodiments, the ledge angle can be 15 degrees, 16 degrees, 17 degrees, 18 degrees, 19 degrees, 20 degrees, 21 degrees, 22 degrees, 23 degrees, 24 degrees, 25 degrees, 26 degrees, 27 degrees, 28 degrees, 29 degrees, 30 degrees, 31 degrees, 32 degrees, 33 degrees, 34 degrees, 35 degrees, 36 degrees, 37 degrees, 38 degrees, 39 degrees, 40 degrees, 41 degrees, 42 degrees, 43 degrees, 44 degrees, or 45 degrees. 
     The toe and heel slits  5666 ,  5662  are positioned on the rear  5610  of the club head  5600  roughly halfway upward from the ground plane  10  towards the top rail  5615 . The toe and heel slits  5666 ,  5662  span short lengths across the toe and heel regions  5604 ,  5604  of the club head  5600 , respectively. The toe and heel slits  5666 ,  5662  extend from either end of the ledge  5825 . The toe slit  5666  is positioned in the toe region  5604  between the upper perimeter portion  5609  and the lower region  5613  of the club head  5600 . The heel slit  5662  is positioned in the heel region  5602  between the upper perimeter portion  5609  next to and adjacent the hosel. 
     The toe slit  5666  and the heel slit  5662  are oriented in a toe-to-heel direction. The toe slit  5666  can be positioned between approximately halfway and approximately ⅔ of the way upwards from the ground plane  10  towards the top rail  5615 , measured parallel to the strikeface  5612 . The heel slit  5662  can also be positioned between approximately halfway up and approximately ⅔ of the way upwards from the ground plane  10  towards the top rail  5615 . In some embodiments, the heel slit  5662  is positioned lower with respect to the ground plane  10  than the toe slit  5666 . In these embodiments, the upper perimeter portion  5609  extends lower in the heel region  5602  than in the toe region  5604 . 
     The toe slit  5666  has a depth  6267  such that a deepest surface of the slit  5666  blends into the indention  5630 . The toe slit depth  6267  can be measured from the outer surface of the upper perimeter portion a lowest point inside the toe slit. The toe slit depth  6267  can range between 0.05 inch and 0.20 inch. For example, the toe slit depth  6267  can range between 0.05 inch and 0.15 inch, or 0.15 inch and 0.20 inch. A toe slit height  5668  can be measured in a direction generally orthogonal to the ground plane from the intersection of the upper perimeter portion  5609  and the toe slit  5666  to the intersection of the ledge  5825  and the toe slit  5666 . The toe slit height  5668  can range between 0.10 inch and 0.30 inch. For example, the toe slit height  5668  can range between 0.15 inch and 0.17 inch, 0.10 inch and 0.15 inch, 0.15 inch and 0.20 inch, or 0.20 inch and 0.30 inch. The toe slit  5666  can comprise a length  5669  between the outer edge of the toe region  5604  to the indention  5630  where the toe slit  5666  terminates, as shown in  FIG.  42   . The toe slit length  5669  can range between 0.318 inch and 0.418 inch. For example, the toe slit length  5669  can be 0.318 inch, 0.320 inch, 0.330 inch, 0.340 inch, 0.350 inch, 0.360 inch, 0.368 inch, 0.370 inch, 0.380 inch, 0.390 inch, 0.400 inch, 0.0410 inch, or 0.418 inch. The dimensions of the toe slit  5666  can affect the deflection of the strikeface  5612 , as described below. 
     The heel slit  5662  is similar in depth and orientation to the toe slit  5666 . However, in some embodiments, the angular orientation of the heel slit  5662  with respect to the ground plane differs slightly from the angular orientation of the toe slit  5666 . In some embodiments, the heel slit  5662  does not extend to a heel-most point of the club head  5600 . A heel slit height  5664  can be measured in a direction generally orthogonal to the ground plane from the intersection of the upper perimeter portion  5609  and the heel slit  5662  to the intersection of the ledge  5825  and the heel slit  5662 . The heel slit height  5664  can range between 0.10 inch and 0.30 inch. For example, the heel slit height  5664  can range between 0.13 inch and 0.16 inch, 0.10 inch and 0.15 inch, 0.15 inch and 0.20 inch, or 0.20 inch and 0.30 inch. The heel slit can comprise a length  5665 , measured from adjacent an edge of the perimeter portion towards the heel region, as shown in  FIG.  42   . The heel slit length  5665  can be longer than the toe slit length  5669 . In other embodiments, the heel and toe slits are the same length. The heel slit length  5665  can range between 0.325 inch and 0.425 inch. For example, the heel slit length  5665  can be 0.325 inch, 0.330 inch, 0.335 inch, 0.340 inch, 0.345 inch, 0.350 inch, 0.355 inch, 0.360 inch, 0.365 inch, 0.370 inch, 0.375 inch, 0.380 inch, 0.385 inch, 0.390 inch, 0.395 inch, 0.400 inch, 0.405 inch, 0.410 inch, 0.415 inch, 0.420 inch, or 0.425 inch. The dimensions of the heel slit  5662  can affect the deflection of the strikeface  5612 , as described below. 
     In the lower region  5613  of the club head  5600 , the body  5601  extends a greater perpendicular distance from the strikeface  5612  than the upper perimeter portion  5609  or the indention  5630 . The lower region  5613  comprises, in part, a solid region adjacent the sole  5606  and the rear  5610  of the club head  5600 . The solid region provides perimeter weighting to the club head  5600 . The solid region is bounded by the sole  5606  and a lower exterior wall  5727 . A front edge of the solid region defines a part of the internal wall of the internal cavity  5616 . 
     The cross-section of golf club head  5600  in  FIG.  44    further illustrates the rear  5610 . The rear  5610  can be divided and understood with respect to the upper region  5611  and the lower region  5613  of the club head  5600 . The upper region  6511  of the rear comprises the upper perimeter portion  5609  and the indention  5630 , including the ledge  5825 . As illustrated in  FIG.  44   , the upper perimeter portion  5609  comprises the top rail  5615 , a rear wall  5723 , and a top wall  5719 . The indention  5630  is formed by the top wall  5719  of the upper perimeter portion, an indention wall  5821 , and a ledge  5825 . 
     As seen in  FIG.  44   , from a cross-sectional view, the upper region  5611  of rear  5610  comprises the top rail  5615 , the rear wall  5723 , the top wall  5719 , the indention wall  5821 , and the ledge  5825 . The rear wall  5723  of rear  5610  is located below and adjacent to the top rail  5615 . The top wall  5719  of rear  5610  is located below and adjacent to the rear wall  5723 . The indention wall  5821  is located below and adjacent to the top wall  5719 . The ledge  5825  is located below and adjacent to the indention wall  5821 . In short, the top wall  5719  and the ledge  5825  are angled towards the strikeface and connect to the indention wall  5821 , to form the indention  5630 . The upper region  5611  further comprises a first reference point  5722  located between top rail  5615  and rear wall  5723 , a second reference point  5782  located between rear wall  5723  and top wall  5719 , a first inflection point  5786  located between top wall  5719  and the indention wall  5821 , a second inflection point  5792  located between the indention wall  5821  and the ledge  5825 , and a third inflection point  5794  located between the ledge  5825  and the lower region  5613 . 
     In some embodiments, top rail  5615  of the upper perimeter portion can be a flatter and taller top rail or skirt than in irons known to one skilled in the art. The flatter and taller rail can compensate for mishits of strikeface  5612  to increase playability off the tee. In some embodiments, the length of top rail  5615 , measured from heel region  5602  to toe region  5604 , can be 70% to 95% of the length of golf club head  5600 . In many embodiments, indention  5630  comprises a top rail box spring design. For some fairway iron-type golf club head embodiments, indention  5630  can be a reverse scoop or indentation of rear  5610  with body  5601  comprising a greater thickness toward sole  5606 . In many embodiments, the top rail of the upper perimeter portion and the indention  5630  provide an increase in the overall bending of strikeface  5612 . In some embodiments, the bending of strikeface  5612  can allow for a 2% to 5% increase of energy. The indention  5630  allows for strikeface  5612  to be thinner and allow additional overall bending. 
     The top rail  5615  of the upper perimeter portion comprises a thickness  6052 . The thickness  6052  of the top rail  5615  can range from 0.040 inch to 0.080 inch. For example, the thickness  6052  of the top rail  5615  can be 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.051 inch, 0.054 inch, 0.057 inch, 0.060 inch, 0.063 inch, 0.066 inch, 0.069 inch, 0.071 inch, 0.074 inch, 0.077 inch, or 0.080 inch. In many embodiments, the thickness  6052  of the top rail  5615  is constant throughout. In other embodiments, the thickness  6052  of the top rail  5615  can vary. In the exemplary embodiment, the thickness  6052  of the top rail  5615  decreases from the strikeface  5612  toward the rear wall  5823 . In many embodiments due to the thickness  6052  of the top rail, top rail  5615  can provide an increase in the overall bending of strikeface  5612 . 
       FIG.  45    illustrates a view of top rail  5615  and a portion of rear  5610  of the cross-section of golf club head  5600  of  FIG.  42   , along a cross-sectional line LVIII-LVIII in  FIG.  42    that is similar to the cross-section of  FIG.  44   . In many embodiments, golf club head  5600  comprises a rear angle  5940 , a top rail angle  5945 , and a strikeface angle  5950 . Rear angle  5940  is measured from top wall  5819  to rear wall  5823  of upper region  5611 . In many embodiments, rear angle  5940  can range from 70 degrees to 140 degrees. In some embodiments, rear angle  5940  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, or 140 degrees. In some embodiments, the rear angle  5940  is approximately 122 degrees. 
     The strikeface  5612  further comprises a strikeface angle  5950 . Strikeface angle  5950  is measured from the strikeface  5612  to the top rail  5615 , wherein the strikeface angle  5950  can range from 70 degrees to 160 degrees or 70 degrees to 110 degrees. In some embodiments, strikeface angle  5950  can be 70 degrees, 75 degrees, 80 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, or 160 degrees. In some embodiments, the strikeface angle  5950  is approximately 90 degrees. 
       FIG.  45    further illustrates the top rail  5615  comprising a top rail angle  5945 . The top rail angle  5945  is measured from rear wall  5823  to the top rail  5615 . In many embodiments, the top rail angle  5945  can range from 70 degrees to 160 degrees or 90 degrees to 110 degrees. In some embodiments, top rail angle  5945  can be 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, or 160 degrees. In some embodiments, the top rail angle  5945  is approximately 131 degrees. 
     The rear wall  5723  extends from the first reference point  5722  to the second reference point in an orientation roughly parallel to the strikeface. The rear wall  5723  connects the top rail and the top wall  5719 . The rear wall  5823  of the upper region  5611  comprises a height  5880 . The height  5880  of the rear wall  5823  is measured from the first reference point  5722  to the second reference point  5782 . The height  5880  of the rear wall  5823  can range from 0.055 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.080 in to 0.085 or 0.55 inch to 0.85 inch. For example, the height  4680  of the rear wall  4623  can be 0.55 inch, 0.58 inch, 0.61 inch, 0.64 inch, 0.67 inch, 0.70 inch, 0.73 inch, 0.76 inch, 0.79 inch, 0.82 inch, or 0.85 inch. In some embodiments, the height  5880  of the rear wall  4623  range from 35% to 60%, 35% to 45%, 45% to 68%, 40% to 55%, 30% to 40%, 35% to 45%, 40% to 50%, 45% to 55%, or 50% to 60% of the total height of the golf club head  5600 . For example, the height  5880  of the rear wall  5823  can be 35%, 38%, 41%, 44%, 47%, 50%, 53%, 56%, or 60% of the total height of the golf club head  5600 . 
     The rear wall  5823  of the upper region  5611  can also comprise a height  5680 A. The height  5680 A is measured from the apex  5828  of the top rail  5615  to the second reference point  5782 . The height  5880 A can range from 0.60 inch to 1.0 inch. For example, the height  5880 A can be 0.60 inch, 0.61 inch, 0.64 inch, 0.67 inch, 0.70 inch, 0.73 inch, 0.76 inch, 0.79 inch, 0.82 inch, 0.85 inch, 0.90 inch, 0.95 inch, or 1.0 inch. In some embodiments, the height  5880 A can range from 40% to 75% of the total height of the golf club head  5600 . For example, the height  5880 A can be 40%, 44%, 47%, 50%, 53%, 56%, 60%, 65%, 70%, or 75% of the total height of the golf club head  5600 . 
     The rear wall  5823  of the upper region  5611  further comprises a rear wall thickness  5856 . The rear wall thickness  5856  is the perpendicular distance of the rear wall  5823  from the outer surface  5603  to the inner surface  5619  of the internal cavity  5630 . The rear wall thickness  5856  can range from 0.040 inch to 0.080 inch. For example, the rear wall thickness  5856  can be 0.040 inch, 0.043 inch, 0.046 inch, 0.049 inch, 0.051 inch, 0.054 inch, 0.057 inch, 0.060 inch, 0.063 inch, 0.066 inch, 0.069 inch, 0.071 inch, 0.074 inch, 0.077 inch, or 0.080 inch. In many embodiments, the rear wall thickness  5856  is constant throughout. In other embodiments, the rear wall thickness  5856   5823  can vary. In the exemplary embodiment, the rear wall thickness  5856  is a constant 0.05 inch. The rear wall thickness  5856  allows energy from an impact to transfer to the inflection point  5886  to help induce a buckling effect. 
     The top wall  5719  is angled toward the strikeface and away from the top rail  5615  in a direction toward the first inflection point  5786 . The top wall  5719  extends from the second reference point  5782  to the first inflection point  5786 . The described configuration of the rear wall  5723  and top wall  5719  allows increased bending of the top rail  5615  of the club head  5600  on impact with a golf ball, compared with a club head devoid of the described rear and top wall configuration. The top wall  5719  connects to the indention wall  5821  at the first inflection point  5786 . 
     The indention  5630  is formed by the top wall  5719 , the indention wall  5821 , and the ledge  5825 . In some embodiments, the indention wall  5821  can be roughly planar. In some embodiments, the indention wall  5821  can comprise an at least partially curved profile, when viewed from a cross-sectional view, as shown in  FIG.  44   . An indention wall thickness  5858  is measured perpendicularly from the exterior surface  5603  to the interior surface  5819  at a point along the indention wall  5821  between the first inflection point  5786  and the second inflection point  5792 . The indention wall thickness  5858  can range from 0.040 inch, to 0.080 inch. For example, the indention wall thickness  5858  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.055 inch, 0.060 inch, 0.65 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. In many embodiments, the indention wall thickness  5858  is constant with the rear wall thickness  5856  and a ledge thickness  5860 . In other embodiments, the indention wall thickness  5858  can be less than the rear wall thickness  5856  and the ledge thickness  5860 . The indention wall thickness  5858  being consistent with or less than the thickness  5823 ,  5860  of the rear wall  5723  and the ledge  5825  allows for more uniform energy transfer and bending. 
     As best understood from a rear view, such as  FIG.  42   , the indention wall  5821  can cover a surface area between 10% and 40% of the surface area of the rear  5610 . For example, the indention wall  5821  can cover a surface area between 10% and 20%, 20% and 30%, or 30% and 40% of the surface area of the rear  5610 . In some embodiments, the indention wall  5821  can cover a surface area approximately 29% of the surface area of the rear  5610 . 
     A height  5888  of the indention  5630  is measured perpendicular to the ground plane  10  from the second reference point  5782  to the third inflection point  5794 . The height  5888  of the indention  5630  can range from 0.15 inch to 1.1 inch. For example, the height  5888  of the indention  5630  can range from 0.15 inch to 0.30 inch, 0.30 inch to 0.45 inch, 0.45 inch to 0.60 inch, 0.60 inch to 0.75 inch, 0.75 inch to 0.90 inch, or 0.90 inch to 1.0 inch. For example, the height  5888  of the indention  5630  can be approximately 0.21 inch in the heel region  5602 , approximately 0.63 inch in a center of the club head between the heel region  5602  and the toe region  5604 , and approximately 0.98 inch in the toe region  5604 . In some embodiments, the maximum height  5888  of the indention is between 0.80 inch and 1.1 inch. 
     The second inflection point  5792  comprises a second inflection angle measured from the indented wall  5721  to the ledge  5825 . The second inflection angle of the second inflection point  5792  can range from at least 95 degrees to 150 degrees. In some embodiments, the second inflection angle  5796  can be at least 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, or 150 degrees. In some embodiments, the second inflection angle can be consistent from the heel region  5602  to the toe region  5604 . In other embodiments, the second inflection angle  5796  can vary from the heel region  5602  to the toe region  5604 . In many embodiments, the second inflection angle  5796  allows for the second inflection point  5686  to act as a buckling point or plastic hinge upon the golf club head  5600  impacting the golf ball at strikeface  5712 . 
     As illustrated in  FIG.  44   , in some embodiments, the ledge comprises a ledge width  5829 . The ledge width  5829  is measured along the ledge  5825  from the second inflection point  5792  to the third inflection point  5794 . The ledge width  5829  can range from 0.088 inch to 0.128 inch. For example, the ledge width  5829  can be 0.090, 0.094 inch, 0.098 inch, 0.100 inch, 0.104 inch, 0.108 inch, 0.110 inch, 0.112 inch, 0.114 inch, 0.118 inch, 0.120 inch, 0.124 inch, or 0.128 inch. In some embodiments, the ledge width  5829  can remain constant from the heel region  5602  to the toe region  5604 . In other embodiments, the ledge width  5829  can vary from the heel region  5602  to the toe region  5604 . For example, the ledge width  5829  can increase from the heel region  5602  to the toe region  5604 . In other embodiments, the ledge width  5829  can decrease from the heel region  5602  to the toe region  5602 . 
     The ledge  5825  comprises a ledge thickness measured perpendicularly from the exterior surface  5603  to the interior surface  5819  at a point along the ledge  5825  between the second inflection point  5792  and the third inflection point  5794 . The ledge thickness can be similar to the indented wall thickness. 
     The upper region  5611  and the lower region  5613  of the rear  5610  are separated by the third inflection point  5794 . In many embodiments, the third inflection point  5794  is positioned at least 40% down on the body  5601  below the apex  5828 . For example, the third inflection point  5694  can be positioned 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, or 70% down on the body  5601  below the apex  5828 . The low positioned third inflection point  5794  allows for more leverage on the upper region  5611  to experience increased bending during impact with a ball, compared to a similar golf club head having a higher inflection point position. 
     The lower region  5613  of the body  5601  begins at the third inflection point  5794  and comprises a lower exterior wall  5827 . The lower exterior wall  5827  extends from the first inflection point  5794  to the sole  5606 . The lower exterior wall  5827  can be angled with respect to the strikeface. The lower region  5613  comprises a height measured from the ground plane  5703  to the third inflection point  5794  adjacent a lowest end of the ledge  5825 . The lower region  5613  height can range between 0.40 inch and 1.20 inch. For example, the lower region  5613  height can range between 0.40 inch and 0.70 inch, 0.60 inch and 0.80 inch, 0.70 inch and 0.90 inch, 0.80 inch and 1.00 inch, 0.90 inch and 1.10 inch, or 1.00 inch and 1.20 inch. 
     A third inflection angle  5851  is measured between the ledge  5825  and the lower exterior wall  5727 , at the third inflection point  5794 . In some embodiments, the third inflection angle  5851  can be less than 160 degrees. In a number of embodiments, the third inflection angle  5851  can be 90 degrees to 175 degrees. For example, the third inflection angle  5851  can be 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, 160 degrees, 165 degrees, 170 degrees, or 175 degrees. 
     The lower exterior wall  5727  is located in the lower region  5613  of the club head  5600 . The lower exterior wall  5727  extends downward from the third inflection point  5794  at an edge of the ledge  5825  to the sole of the club head  5600 . A section of the lower exterior wall  5727  forms an outer rear edge of the solid region of the lower region  5613 . The lower exterior wall  5727  bounds the rear of the club head  5600  below the ledge  5825 . 
       FIG.  46    illustrates another cross-sectional view of the golf club head  5600 , similar to the detailed cross-section of golf club head  5600  illustrated in  FIG.  42   . The internal cavity  5616  comprises a top cavity width  5993 , a minimum cavity width (minimum gap)  5990 , a maximum cavity width  6095 , and a lower region cavity width  6097 , all measured in a direction perpendicular from the strikeface  5612  from an interior surface  5819  of the strikeface  5612  to a back edge of the internal cavity  5616 . The top cavity width  5993  is located above the minimum upper cavity width  5990 . The region of the internal cavity  5616  having the greater top cavity width  5993  corresponds to the upper perimeter portion  5609 . The portion of the internal cavity  5616  adjacent the minimum upper cavity width  5990  corresponds to the indention  5630 . The top cavity width  5993  is above the minimum cavity width  5990 , which is above the maximum cavity width  6095 , which is above the lower region cavity width  6097 . In some embodiments, the maximum cavity width  5990  is located in the lower region  5613  of the club head  5600 . In many embodiments, the lower region  5613  of the body  5601  comprises a solid region adjacent the rear  5610 . The solid region provides weighting to the rear  5610  of the club head  5600 . This solid region causes the lower region cavity width  6097  to be less than a width of the cavity adjacent and below the indention  5630 . The minimum cavity width  5990  can be between 20% and 55% of the lower region cavity width  6097  in a central portion of the club head  5600 , such as is shown in the cross-section of  FIG.  46   . For example, the minimum cavity width  5990  can be 20%, 25%, 30%, 35%, 40%, 45%, or 50% of the lower region cavity width  6097 . 
     The top cavity width  5993  is measured between the rear wall  5723  and a back surface of the strikeface  5612 . In some embodiments, top cavity width  5993  can range from 0.079 inch (2 mm) to 0.24 inch (6 mm). For example, top cavity width can be 0.079 inch (2 mm), 0.118 inch (3 mm), 0.16 inch (4 mm), 0.197 inch (5 mm) or 0.24 inch (6 mm). In other embodiments, top cavity width can range from 0.118 inch (3 mm) to 0.16 inch (4 mm). In some embodiments, top cavity width can be 0.135 inch (3.429 mm). 
     In some embodiments, the minimum cavity width  5990  is located between the first inflection point  5786  and the back surface of the strikeface  5612 . In some embodiments, the minimum cavity width  5990  is located between the indention wall  5821  and the back surface of the strikeface  5612 . In some embodiments, minimum cavity width  5990  can range from 0.079 inch (2 mm) to 0.24 inch (6 mm). For example, minimum cavity width  5990  can be 0.079 inch (2 mm), 0.118 inch (3 mm), 0.16 inch (4 mm), 0.197 inch (5 mm) or 0.24 inch (6 mm). In other embodiments, minimum cavity width  5990  can range from 0.118 inch (3 mm) to 0.16 inch (4 mm). In some embodiments, minimum cavity width  5990  can be 0.135 inch (3.429 mm). 
     The maximum cavity width  6095  is located beneath the indention  5630 . In some embodiments, maximum cavity width  6095  can range from 0.40 inch to 0.70 inch. For example, the maximum cavity width can be 0.40 inch, 0.45 inch, 0.50 inch, 0.55 inch, 0.60 inch, 0.65 inch, or 0.70 inch. In other embodiments, maximum cavity width  6095  can range from 0.55 inch to 0.60 inch. In some embodiments, maximum cavity width  6095  can be 0.59 inch. 
     The lower region cavity width  6097  is measured between the solid region and the interior surface  5819  of the strikeface  5612 . In some embodiments, lower region cavity width  6097  can range from 0.15 inch to 0.40 inch. For example, the lower region cavity width  6097  can be 0.15 inch, 0.20 inch, 0.25 inch, 0.30 inch, 0.35 inch, or 0.40 inch. In other embodiments, lower region cavity width  6097  can range from 0.27 inch to 0.31 inch. In some embodiments, top cavity width can be 0.29 inch. 
     Referring again to  FIG.  46   , the body  5601  of golf club head  5600  further comprises an upper perimeter portion distance  6092 , a minimum distance  6094 , and a maximum distance  6096 . The upper perimeter portion distance  6092  of the club head  5600  adjacent to the top rail  5615  is measured as the perpendicular distance from the exterior surface  5603  of the strikeface  5612  to the exterior surface  5603  of the rear wall  5623 . The upper perimeter portion distance  6092  of the club head is between 0.305 inch and 0.325 inch. In some embodiments, the upper perimeter portion distance  6092  of the club head is between 0.305 inch and 0.310 inch, 0.310 inch and 0.315 inch, 0.315 inch and 0.320 inch, or 0.320 inch and 0.325. In some embodiments, the upper perimeter portion distance  6092  of the club head  5600  is greater than the ledge width  5829 . 
     The minimum distance  6094  of the body  5601  is measured as the perpendicular distance from the exterior surface  5603  of the strikeface  5612  in the upper region  5611  to the exterior surface  5603  of the rear wall  5623 . The minimum distance  6094  can range from 0.20 inch to 0.40 inch. For example, the minimum distance  6094  can be 0.20 inch, 0.22 inch, 0.24 inch, 0.26 inch, 0.28 inch, 0.30 inch, 0.32 inch, 0.34 inch, 0.36 inch, 0.038 inch, or 0.40 inch. In some embodiments, the minimum distance  6094  of the body  5601  can be greater than the ledge width  5829 . The maximum distance  6096  of the body  5601  is measured as the perpendicular distance from the exterior surface  5603  of the strikeface  5612  to the exterior surface  5603  of the rear  5610 . The maximum distance  6096  can range from 0.60 inch to 0.90 inch. For example, the maximum distance  6096  can be 0.60 inch, 0.64 inch, 0.68 inch, 0.72 inch, 0.76 inch, 0.80 inch, 0.84 inch, 0.88 inch, or 0.90 inch. 
     As illustrated in  FIG.  44 - 48   , the golf club head  5600  can be a hollow, or at least partially hollow body comprising an internal cavity  5616 . Internal cavity  5616  of the body  5601  comprises a volume. The volume of the internal cavity  5616  can range from 0.65 inch 3  (10.65 cm 3 ) to 1.05 inch 3  (17.21 cm 3 ). In some embodiments, the internal cavity  5616  can comprise a volume of 0.65 inch 3  (10.65 cm 3 ), 0.70 inch 3  (11.47 cm 3 ), 0.75 inch 3  (12.29 cm 3 ), 0.80 inch 3  (13.11 cm 3 ), 0.85 inch 3  (13.93 cm 3 ), 0.90 inch 3  (14.75 cm 3 ), 0.95 inch 3  (15.57 cm 3 ), 1.00 inch 3  (16.39 cm 3 ), or 1.05 inch 3  (17.21 cm 3 ). Similarly, material portion of the body  5601 , void of the cavity  5616 , further comprises a material volume. The material volume of the body  5601  can range from 2.50 inch 3  (40.97 cm 3 ) to 3.50 inch 3  (57.35 cm 3 ). For example, the material volume of the body  5601  can be 2.50 inch 3  (40.97 cm 3 ), 2.60 inch 3  (42.61 cm 3 ), 2.70 inch 3  (44.25 cm 3 ), 2.80 inch 3  (45.88 cm 3 ), 2.90 inch 3  (47.52 cm 3 ), 3.00 inch 3  (49.16 cm 3 ), 3.10 inch 3  (50.80 cm 3 ), 3.20 inch 3  (52.44 cm 3 ), 3.30 inch 3  (54.08 cm 3 ), 3.40 inch 3  (55.72 cm 3 ), or 3.50 inch 3  (57.35 cm 3 ). 
     In many embodiments, the internal cavity  5616  of the body  5601  can be void of any substance. In other embodiments, the internal cavity  5616  of the body  5601  can comprise a polymer (not pictured), wherein the polymer can be at least partially filling the internal cavity  5616 . The polymer can be polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, polycarbonate, polypropylene, other thermoplastics, composites polymers or any combination thereof. The polymer can fill 10% to 80% 10% to 25%, 15% to 30%, 30% to 45%, 45% to 60%, 60% to 75%, 75% to 80%, 10% to 40%, 30% to 60%, or 40% to 80% of the internal cavity  5616  of the body  5601 . For example, the polymer can fill 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% of the internal cavity  5616  of the body  5601 . In some embodiments, the polymer fills 80% of the internal cavity  5616  of the body  5601 . 
     The polymer at least partially filling the internal cavity  5616  of the body  5601  can comprise a specific gravity ranging from 0.05 to 4. For example, the specific gravity of the polymer can be 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, or 4. In some embodiments, the specific gravity of the polymer is proportional to the mass of the polymer, wherein 1 specific gravity of the polymer is equal to 1 gram. Similarly, in those exemplary embodiments, the volume is proportional to the polymer specific gravity, wherein 1 specific gravity of the polymer is equal to 1 cc. In other embodiments, the volume is not proportional to the specific gravity of the polymer. For example, the ratio of the polymer specific gravity to the polymer volume can be 2:1 cc, 2:3 cc, 2:4 cc, 3:1 cc, 3:2 cc, 3:4 cc, 4:1 cc, 4:2 cc, or 4:3 cc. 
     The mass of the polymer allows for the swing weight of the golf club head  4400  to be customizable for each player. Increasing the volume of the polymer, and thus the mass, increases the swing weight. Similarly, decreasing the volume of the polymer decreases the swing weight. Having the appropriate swing weight for each individual player improves feel during a swing and can improve performance such as swing speed, swing path, ball speed, and ball trajectory. The polymer can further increase the overall mass of the golf club head  5600  more toward the sole  5606 . Increasing the mass more toward the sole shifts the CG low and back, thereby improves the moment of inertia. 
     The strikeface  5612  can be coated with a durable finish. For example, the strikeface  5612  can be coated with Hydropearl 2.0 chrome plate finish or a high polished chrome. In some embodiments, the strikeface  5612  is further finished with brushing or blasting. The golf club head  5600  can further comprise a vibration damping layer  5878  on the interior surface  5819  of the strikeface  5612 . The vibration damping layer  5878  can be formed from an elastomer material or any other suitable material. For example, the vibration damping layer  5878  can be formed from a urethane and graphene coating, a urethane coating, or a silicone gel. The vibration damping layer  5878  can have a weight of 1-7 grams. For example, the vibration damping material can have a weight of 1 gram, 3 grams, 5 grams, or 7 grams. The vibration damping layer  5878  can fill between 10%-30% of the volume of the internal cavity of the club head  5600 . The vibration damping layer  5878  can partially or fully cover the interior surface  5819  of the strikeface  5612 . The thickness of the vibration damping layer  5878 , measured perpendicular to the strikeface  5612 , can either vary or be uniform across the interior surface  5819  of the strikeface  5612 . 
     In some embodiments, the golf club head  5600  can further comprise an aperture  5634  located on the toe region  5604 . The aperture  5634  comprises internal threads and is configured to receive a threaded screw weight  5637 , as seen in  FIG.  42   .  FIG.  42    illustrates the threaded screw weight  5637  removed from the aperture  5634  but positioned for insertion into the aperture  5634 . The threaded screw weight  5637  comprises a mass, wherein the mass of the threaded screw weight  5637  can range from 2 grams to 12 grams. In other embodiments, the mass of the threaded screw weight  5637  can range from 4 grams to 10 grams. In some embodiments, the screw weight  5637  can weight 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, 7 grams, 8 grams, 9 grams, 10 grams, 11 grams, 12 grams, 13 grams, or 14 grams. The mass of the screw weight  5637  correlates with the length of the screw weight  5637 , wherein a longer threaded screw weight  5637  equates to a greater mass. The threaded screw weight  5637  further affects the mass and overall swing weight of the golf club head  5600 . Therefore, the threaded screw weight  5637  can improve the feel of the golf club head  5600 , as well as performance characteristics (e.g., swing speed, ball speed, and ball flight). 
     The hosel of the club head  5600  can house a tip weight  5638 .  FIG.  42    depicts the tip weight  5638  removed from the hosel, but in position for insertion into the hosel. The tip weight  5638  can have a weight that ranges between 0.1 and 10 grams. For example, the tip weight  5638  can have a weight of 0.2, 0.4, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 grams. 
     Although both the toe slit  5666  and heel slit  5662  affect the deflection of the club head  5600 , the toe slit  5666  has a greater effect on the deflection. The slits  5666 ,  5662  reduce concentrated stresses at toe and heel junctions between the lower region  5613  and the upper perimeter portion  5609  and spread impact stresses across a greater volume of the club body  5601 . The toe and heel slits  5666 ,  5662  allow structural bending between the upper region  5611  and the lower region  5613  of the club head  5600 , which results in greater deflection of the strikeface  5612  than would be present in a similar golf club head lacking toe and/or heel slits. The slits  5666 ,  5662  can increase the bending between the lower region  5613  and the upper region  5611  around the second inflection point  5792 . The greater deflection of the strikeface  5612  provides a higher dynamic loft angle to the golf club  5600 . The loft angle is an acute angle measured from the strikeface  5612  to a ground reference plane  10 . By dynamically increasing the deflection of the club head  5600 , the conventional loft angle can be lowered without sacrificing trajectory. For example, a first club head with a loft angle lower than a second club head can have a trajectory equal to the trajectory of the second club head if the first club head comprises slits that increase the deflection of the club head. In some embodiments, the conventional loft angle can be reduced by up to 0.6 degrees, up to 0.5 degrees, or up to 0.4 degrees. The lower loft of the first club head can result in a higher ball speed for a golf ball impacted by the club head due to the lower loft angle of the first club. The gapping between clubs in a set can be more uniform in a club head set that comprises the slits disclosed herein. 
     Furthermore, in many embodiments, indention  5630  can provide an increase in golf ball speed over ball speeds of standard golf club heads and can increase the launch angle over both the standard hybrid and iron club heads. A golf club head lacking the indention  5630  cannot buckle in a controlled manner during impact or spring back like a drum after impact as well as the club head  5600 . The first, second, and third inflection points  5786 ,  5792 , and  5794  allow the body  5601  to bend backwards when a golf ball impacts the strikeface in a manner not possible for a golf club head lacking these inflection points. 
     The upper perimeter portion can provide spring to the back end of the club and exhibit low peak stress concentrations. The interaction of the strikeface  5612 , the top rail  5615 , the rear wall  5723 , and the top wall  5719  is affected by the strikeface angle  5950 , the top rail angle  5945 , and the rear angle  5940 . The strikeface  5612 , the top rail  5615 , the rear wall  5723 , and the top wall  5719  interact and benefit the hinging of the club head in a manner similar to the respective components of golf club head  3700  described above. 
     The uniform thinned region  6060  on the sole  5606 , described above, can provide multiple benefits, similar to those described above for the uniform thinned regions of golf club heads  2200 ,  2700 ,  3200 ,  3700 ,  4400 , and  4900 . 
     In some embodiments, body  5601  can comprise stainless steel-titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, body  5601  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, strikeface  4412  can comprise stainless steel, titanium, aluminum, a steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, strikeface  4412  can comprise carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In some embodiments, body  5601  can comprise the same material as strikeface  5612 . In some embodiments, body  5601  can comprise a different material than strikeface  5612 . 
     II. Golf Club Head with Partial Back Cavity 
       FIGS.  49 - 60 D  illustrate a golf club head  7100  that includes a partial back cavity  7102  and a rear opening  7104  according to embodiments of the present invention. In the illustrated embodiment, the club head  7100  is an iron-type club head  7100 . The club head  7100  includes a body  7106 , a faceplate  7108  coupled to the body  7106  at a front end  7110  and defining a striking surface or strikeface  7112 , and a cover or badge  7114  coupled to the body  7106  at a back end  7116  opposite the front end  7110 . In some embodiments, body  7106  can be similar to body  1001  ( FIG.  1   ), body  2201  ( FIG.  8   ), body  2701  ( FIG.  13   ), body  3201  ( FIG.  18   ), body  3701  ( FIG.  23   ), and/or body  4401  ( FIG.  30   ). In some embodiments as will be described below, the badge  7114  may be a partial badge  7114  ( FIGS.  59 A- 59 C ), or the badge  7114  may be omitted entirely from the club head  7100  ( FIG.  59 D ). In addition to the front end  7110  and the back end  7116 , the body  7106  includes a heel region  7118 , a toe region  7120  opposite the heel region  7118 , a sole  7122 , and a top rail  7124  opposite the sole  7122 . The body  7106  also includes a hosel  77126  proximate the heel region  7118  for coupling the golf club head  7100  to a shaft (not shown) to form a golf club. 
     With reference to  FIG.  52   , the rear opening  7104  is defined by the body  7106  and is formed in the back end  7116 . The body  7106  further defines a front opening  7128  formed in the front end  7110  and located opposite the rear opening  7104 . The faceplate  7108  covers and closes the front opening  7128 . In some embodiments as will be described below, the badge  7114  partially or fully covers and closes the rear opening  7104 . The faceplate  7108  and the body  7106  together define the partial back cavity  7102 . The partial back cavity  7102  is also described as a partially closed internal space formed within the body  7106  and partially bounded by the faceplate  7108 . The partial back cavity  7102  is referred to herein as ‘partial’ in the sense that it remains partially open to the exterior of the club head  7100  due to the existence of the rear opening  7104 , which communicates the partial back cavity  7102  with the exterior of the club head  7100 . In other embodiments (not shown), the body  7106  can be formed integrally with a faceplate such that the body alone defines the partial back cavity  7102 . 
     With reference to  FIGS.  54  and  55   , the body  7106  also defines an open external cavity  7130 , hereafter referred to as an indention  7130 , extending inward from the back end  116  toward the front end  7110  and toward the strikeface  7112 . The rear opening  7104  is formed within the indention  7130 . The indention  7130  alters the deflection and/or weighting of the club head  7100 . Specifically, the indention  7130  allows the club head  7100  to buckle in a controlled manner during impact with a golf ball, or spring back like a drum after impact. Thus, the indention  7130  can provide a relative increase in golf ball speed and in launch angle as compared to known prior art iron-type golf club heads. 
     With reference to  FIGS.  55  and  58   , the body  7106  includes a back wall  7132  formed at the back end  7116 . The back wall  7132  surrounds and defines the indention  7130  and generally extends between the top rail  7124  and the sole  7122 , and between the heel region  7118  and the toe region  7120 . The back wall  7132  is further divided into an upper back wall  7134  formed adjacent the top rail  7124 , and a lower back wall  7136  formed adjacent the sole  7122 . The upper back wall  7134  extends downward from the top rail  7124  to a top ledge or top cavity wall  7138 . In the illustrated embodiment, the upper back wall  7134  is generally parallel to the strikeface  7112 . In other embodiments, the upper back wall  7134  can generally slope toward or away from the strikeface  7112  as the upper back wall  7134  extends from the top rail  7124  to the top cavity wall  7138 . The lower back wall  7136  extends upward from the sole  7122  to a bottom ledge or bottom cavity wall  7140 . In the illustrated embodiment, the lower back wall  7136  generally slopes away from the strikeface  7112  as the lower back wall  7136  extends from the sole  7122  toward the bottom cavity wall  7140 . In other embodiments, the lower back wall  7136  can be generally parallel to the strikeface  7112  or the lower back wall  7136  can slope toward the strikeface  7112 . 
     With continued reference to  FIG.  58   , the top cavity wall  7138  extends from the upper back wall  7134  to an upper indention wall  7142  in a direction generally toward the strikeface  7112 . The top cavity wall  7138  generally follows the contour of the top rail  7124  as the top cavity wall  138  extends between the heel region  7118  and the toe region  7120 . The bottom cavity wall  7140  extends from the lower back wall  7136  to a lower indention wall  7144  in a direction generally toward the strikeface  7112 . The bottom cavity wall  7140  generally follows the contour of the sole  7122  as the bottom cavity wall  7140  extends between the heel region  7118  and the toe region  7120 , except that the bottom cavity wall  7140  includes a stepped portion  146  ( FIG.  54   ) located toward the toe region  7120  that steps upward toward the top rail  124 . 
     A rear opening rim  7148  ( FIG.  54   ) further defines and circumscribes the rear opening  7104 . The rear opening rim  7148  is divided into an upper rim  7150  located closer to the top rail  7124 , and a lower rim  7152  located closer to the sole  7122  ( FIGS.  57 ,  58   ). The upper rim  7150  generally follows the contour of the top rail  7124  and of the top cavity wall  7138 . The lower rim  7152  generally follows the contour of the bottom cavity wall  7140 , and can include a generally linear, arcuate, or segmented extent (e.g., a step-wise extent) as the lower rim  7152  extends between the heel region  7118  and the toe region  7120 . The upper indention wall  7142  extends from the top cavity wall  7138  to the upper rim  7150  of the rear opening  7104 , in a direction generally toward the sole  7122 . The upper indention wall  7142  is generally parallel to the upper back wall  7134 . The upper indention wall  7142  is also generally parallel to the strikeface  7112 . In other embodiments, the upper indention wall  7142  can slope generally away from the strikeface  7112  as the upper indention wall  7142  extends from the top cavity wall  7138  to the upper rim  7150 . The lower indention wall  7144  extends from the bottom cavity wall  7140  to the lower rim  7152  of the rear opening  7104 , in a direction generally toward the top rail  7124 . The lower indention wall  7144  generally slopes toward the strikeface  7112  as the lower indention wall  7144  extends from the bottom cavity wall  7140  to the lower rim  7152 . Together, the top and bottom cavity walls  7138 ,  7140  and the upper and lower indention walls  7142 ,  7144  cooperate to define the indention  7130 . In embodiments that include the badge  7114 , the badge  7114  further defines the indention  7130 , and closes off the indention  7130  from the partial back cavity  7102 . Furthermore, in some embodiments that include the badge  7114 , the badge  7114  further defines the indention  7130 , and closes off the indention  7130  from the partial back cavity  7102 , by being positioned within the rear opening rim  7148 . In some embodiments, the badge  7114  can be adhered to the upper rim  7150  and the lower rim  7152 . 
     With continued reference to  FIG.  58   , the body  7106  further includes a front wall  7154  formed at the front end  7110 . The front wall  7154  surrounds the front opening  7128  and generally extends between the top rail  7124  and the sole  7122 , and between the heel region  7118  and the toe region  7120 . The front wall  7154  is further divided into an upper front wall  7156  formed adjacent the top rail  7124 , and a lower front wall  7158  formed adjacent the sole  7122 . A front opening rim  7160  defines and circumscribes the front opening  7128 . The upper front wall  7156  extends downward from the top rail  7124  to the front opening rim  7160 . In the illustrated embodiment, the upper front wall  7156  is generally parallel to the strikeface  7112 . The lower front wall  7158  extends upward from the sole  7122  to the front opening rim  7160 . In the illustrated embodiment, the lower front wall  7158  is also generally parallel to the strikeface  7112 . 
     The body  7106  also includes a top rail wall  7162  that extends across the top rail  7124  between the upper front wall  7156  and the upper back wall  7134 . The top rail wall  7162  includes a smoothly curved contour as the top rail wall  7162  extends between the upper front wall  7156  and the upper back wall  7134 . The body  7106  further includes a bottom wall  7164  that extends across the sole  7122  between the lower front wall  7158  and the lower back wall  7136 . The bottom wall  7164  includes a smoothly curved contour as the bottom wall  7164  extends between the lower front wall  7158  and the lower back wall  7136 . 
     A portion of the bottom wall  7164  adjacent the lower front wall  7158  defines a uniform thinned region  7166 . The uniform thinned region  7166  has a sole thickness  7168 , measured perpendicular to an exterior surface of the bottom wall  7164  and between the exterior surface and an interior surface thereof. The sole thickness  7168  is relatively thinner as compared to the thicknesses of the remaining portions of the bottom wall  7164 . The sole thickness  7168  is also relatively thinner as compared to that of known prior art iron-type clubs. In some embodiments, the sole thickness may range from approximately 0.040 inch to 0.080 inch. In other embodiments, the sole thickness  7168  may be within the range of 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.040 inch to 0.055 inch, 0.045 inch to 0.060 inch, 0.050 inch to 0.065 inch, 0.055 inch to 0.070 inch, 0.060 inch to 0.075 inch, or 0.065 inch to 0.080 inch. For example, the sole thickness  7168  can be 0.040 inch, 0.045 inch, 0.050 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, or 0.080 inch. 
     With reference to  FIGS.  57  and  58   , the partial back cavity  7102  includes an upper channel  7170  defined within the top rail  7124  of the body  7106  and generally extending lengthwise across the club head  7100  between the heel region  7118  and the toe region  7120 . The upper channel  7170  is bounded between the top cavity wall  7138  and the top rail wall  7162 , and between the faceplate  7108  and the upper back wall  7134 . Due in part to the upper channel  7170 , the top rail wall  7162  and the upper back wall  7134  cooperate to define a first buckling or first hinge region  7172  of the body  7106 . The first hinge region  7172  experiences increased bending as compared to other regions of the body  7106  when the strikeface  7112  impacts a golf ball. The first hinge region  7172  allows the top rail  7124  to dynamically deflect to a greater extent as compared to known prior art iron-type club heads and enables the top rail  7124  to react to the impact force over a wider volumetric area of the body  7106 . In turn, the top rail  7124  acts as a springboard by returning more recoiled force back to the faceplate  7108  as the top rail  7124  returns to its original orientation, thereby imparting more energy into the golf ball. 
     The deflection of the top rail  7124  also causes the faceplate  7108  to deflect to a greater extent during impact with the golf ball, leading to less spin, a higher loft angle, and greater ball speed for a given club speed as compared to standard iron-type golf club heads. As the first hinge region  7172  bends during impact, the faceplate  7108  deflects, causing a loft angle (defined between the strikeface  7112  and a ground plane with the golf club head  7100  at an address position) to increase relative to that of the club head  7100  at rest. The resting state loft angle of the club head  7100  (prior to impact with the golf ball) is reduced relative to that of typical prior-art iron-type club heads. This reduction of the resting state loft angle accounts for the deflection of the top rail  7124  at the hinge region  7172 , and the resultant, dynamically-increased loft angle experienced while striking a golf ball. In some embodiments, the resting state loft angle can be reduced by up to 0.6 degrees as compared to known prior art iron-type club heads and still achieve a comparable launch angle of the golf ball during impact. Moreover, the club head  7100  including the relatively reduced loft angle can achieve a relatively higher ball speed due to the reduced loft angle. 
     With continued reference to  FIGS.  57  and  58   , the partial back cavity  7102  also includes a lower channel  7174  defined within the sole  7122  of the body  7106  and generally extending lengthwise across the club head  7100  between the heel region  7118  and the toe region  7120 . The lower channel  7174  is bounded between the bottom cavity wall  7140  and the bottom wall  7164 , and between the faceplate  7108  and the lower back wall  7136 . Due in part to the lower channel  7174 , uniform thinned region  7166  defines a second buckling or hinge region  7176  of the body  7106 . Much like the first hinge region  7172 , the second hinge region  7176  experiences increased bending as compared to other regions of the body  7106  when the golf club head  7100  impacts a golf ball. The second hinge region  7176  dynamically deflects to a greater extent as compared to known prior art iron-type club heads and enables the sole  7122  to react to the impact force over a wider volumetric area of the body  7106 . In turn, the sole  7122  acts as a springboard by returning more recoiled force back to the faceplate  7108  as the sole  7122  returns to its original orientation, thereby imparting more energy into the golf ball. 
     With reference to  FIG.  53   , the body  7106  also includes a solid region  7178  located toward the toe region  7120 , the sole  7122 , and the back end  7116  of the body  7106 . The solid region  7178  includes a relatively greater volume of the material forming the body  7106  as compared to other regions of the body  7106 . Thus, the solid region  7178  has a relatively greater mass as compared to other regions of the body  7106  and provides perimeter weighting to the club head  7100 . 
     With reference to  FIGS.  52  and  53   , an external toe cavity  7180  is formed within the body  7106 . The toe cavity  7180  is located generally within the solid region  7178 , toward the toe region  7120  and the sole  7122 . The toe cavity  7180  is cylindrical in shape for receiving a cylindrical toe weight  7182 . In some embodiments, the toe cavity  7180  is threaded for receiving a threaded toe weight  7182 . In other embodiments, the toe weight  7182  is swedged into the toe cavity  7180 . In other embodiments, the toe cavity  7180  can be trapezoidal in shape for receiving a non-cylindrical toe weight  7182 . The body  7106  can include multiple toe cavities for receiving multiple weights. The toe cavity  7180  extends through the solid region  7178  to connect with the partial back cavity  7102 . In other embodiments, the toe cavity  7180  extends partially into the solid region  7178  but does not extend to the partial back cavity  7102 . In some embodiments, the toe weight  7182  can have a mass between 2 and 14 grams. The toe weight  7182  improves the swing weight and overall feel of the golf club head  7100 , as well as other performance characteristics (e.g., swing speed, ball speed, and ball flight). 
     With reference to  FIG.  55   , the strikeface  7112  is generally flat and has a centerpoint  7184  located at a geometric center of the strikeface  7112 . A midplane  7188  coincident with the centerpoint  7184  extends perpendicular to the strikeface  7112  to generally divide the club head  7100  into an upper region and a lower region. The rear opening  7104  is located above the midplane  7188 , so that the rear opening  7104  is located between the midplane  7188  and the top rail  7124 . In other embodiments, at least 50% of the area of the rear opening  7104  is located between the midplane  7188  and the top rail  7124 . In further embodiments, 50%-60%, 60%-70%, 70%-80%, 80%-90%, or 90%-100% of the area of the rear opening  7104  can be positioned between the midplane  7188  and the top rail  7124 . 
     With reference to  FIG.  58   , an area of the rear opening is circumscribed and defined by the rear opening rim  7148 . A projected area  7189  of the rear opening  7104  is defined by projecting the area of the rear opening  7104  onto the strikeface  7112  along a direction parallel to the midplane  7184 , as shown by the dashed lines in  FIG.  58   . The midplane  7184  divides the strikeface  7112  into an upper region  7112 A located above the midplane  7184  and closer to the top rail  7124 , and a lower region  7112 B located below the midplane  7184  and closer to the sole  7122 . The projected area  7189  of the rear opening  7104  is located on the upper region  7112 A. In other embodiments, at least 50% of the projected area  7189  is located on the upper region  7112 A. In further embodiments, 50%-60%, 60%-70%, 70%-80%, 80%-90%, or 90%-100% of the area projected area  7189  can be located on the upper region  7112 A. 
     The strikeface  7112  is coated with a durable finish (e.g., Hydropearl 2.0 chrome plate finish or a high polished chrome). In some embodiments, the strikeface  7112  is further finished with brushing or blasting. The golf club head  7100  also includes a vibration damping layer  7190  applied to an interior surface of the faceplate  7108 . The vibration damping layer  7190  is formed from an elastomer material (e.g., a urethane and graphene coating, a urethane coating, a silicon gel, etc.). The vibration damping layer  7190  can alter and/or reduce the sound (e.g., “clank” or “pinging” noises) generated as the strikeface  7112  impacts the golf ball. The vibration damping layer  7190  can weigh between 1-7 grams and can fill between 10%-30% of the volume of the partial back cavity  7102  of the club head  7100 . The vibration damping layer  7190  can partially or fully cover the interior surface of the faceplate  7108 . The thickness of the vibration damping layer  7190 , measured perpendicular to the faceplate  7108 , can either vary or be uniform across the interior surface of the faceplate  7108 . 
     With reference to  FIGS.  60 A- 60 D , the partial back cavity  7102  of the club head  7100  can be filled with a vibration damping filler material  7192 . In some embodiments, the entire volume of the partial back cavity  7102  is completely filled with the filler material  7192  ( FIG.  60 A ). In other embodiments, most of the volume of the partial back cavity  7102  ( FIG.  60 B ), or approximately one half of the volume (e.g., a lower half of the volume) ( FIG.  60 C ), or approximately one quarter of the volume (e.g., the lower one quarter of the volume) ( FIG.  60 D ) of the partial back cavity  7102  is filled with the filler material  7192 . In other embodiments, the filler material  7192  can fill 10% to 80%, 10% to 25%, 15% to 30%, 30% to 45%, 45% to 60%, 60% to 75%, 75% to 80%, 10% to 40%, 30% to 60%, or 40% to 80% of the partial back cavity  7102 . For example, the filler material  7192  can fill 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% of the partial back cavity  7102 . In some embodiments, the filler material  7192  fills 80% of the partial back cavity  7102 . In yet other embodiments, the partial back cavity  7102  does not contain the filler material. 
     The filler material  7192  can be a synthetic polymer elastomer (e.g., polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, polycarbonate, polypropylene, hot melt, other thermoplastics, composites, polymers or any combination thereof). In other embodiments, the filler material  7192  can be a natural polymer (e.g., rubbers, natural polymers derived from feathers, etc.), or the filler material  7192  can be a non-polymer material (e.g., quartz or other minerals). The filler material  7192  can have a specific gravity ranging from 0.05 to 4. For example, the specific gravity of the filler material  7192  can be 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, or 4. In some embodiments, the specific gravity of the filler material  7192  is proportionally equal to the mass of the filler material  7192 , where 1 specific gravity of the filler material  7192  is equal to 1 gram. Similarly, in those exemplary embodiments, the volume occupied by the filler material  192  is proportionally equal to the specific gravity of the filler material  7192 , wherein 1 specific gravity of the filler material  7192  is equal to 1 cc. In other embodiments, the volume is proportionally greater or less than the specific gravity of the filler material  192 . For example, the ratio of the specific gravity to the volume of the filler material  192  can be 2:1 cc, 2:3 cc, 2:4 cc, 3:1 cc, 3:2 cc, 3:4 cc, 4:1 cc, 4:2 cc, or 4:3 cc. 
     The mass of the filler material  7192  allows a swing weight of the golf club head  7100  to be customizable for each player. Increasing the volume of the filler material  7192  that occupies the open back cavity  7102  increases the overall mass of the club head  7100 , and thus increases the swing weight thereof. Similarly, reducing the volume of the filler material  7192  that occupies the open back cavity  7102  reduces the swing weight of the club head  7100 . Achieving the appropriate swing weight of the club head  7100  for each individual player improves the feel of the golf club during a swing and can improve performance by optimizing swing speed, swing path, ball speed, and ball trajectory. The filler material  7192  can further concentrate the mass of the golf club head  7100  more toward the sole  7122 . Concentrating the mass more toward the sole  7122  shifts a center of gravity (CG) of the club head  100  toward the sole  7122  and toward the back end  7116 , thereby improving a moment of inertia (MOI) of the club head measured about an axis defined by the hosel  7126  of the club head  7100 . 
     The rear opening  7104  provides access to the partial back cavity  7102  for applying the vibration damping layer  7190  to the back surface of the faceplate  7108 . In those embodiments that include the filler material  7192 , the rear opening  7104  also provides access to the partial back cavity  102  for depositing the filler material  7192  into the partial back cavity  7102 . 
     With reference to  FIGS.  57  and  58   , the badge  7114  covers the rear opening  7104 . During assembly of the golf club head  7100 , the badge  7114  is coupled to the body  7106  after the vibration damping layer  7190  is applied to the faceplate  7108 , and after the filler material  7192  is deposited within the partial back cavity  7102 . When the faceplate  7108  and the badge  7114  are both coupled to the body  7106 , the partial back cavity  7102  becomes a fully enclosed internal volume within the golf club head  7100 . The badge  7114  includes an extruded portion  7194  ( FIG.  58   ) that extends into the rear opening  7104 . The badge  7114  can be greater in width than the upper and lower indention walls  7142 ,  7144 , while the extruded portion  7194  can be equal in width to the upper and lower indention walls  7142 ,  7144 . 
     In some embodiments, such as those illustrated in  FIGS.  59 A- 59 C , the badge  7114  is a partial badge  7114  that only covers a portion of the rear opening  7104 . For example, the partial badge  7114  can cover an upper portion of the rear opening  7104  adjacent the upper rim  7150  ( FIG.  59 A ), leaving a lower portion of the rear opening  7104  uncovered. In other embodiments, the partial badge  7114  can cover a lower portion of the rear opening  7104  adjacent the lower rim  7152  ( FIG.  59 B ), leaving an upper portion of the rear opening  7104  uncovered. In further embodiments, the partial badge  7114  can include a central aperture  7196  ( FIG.  59 C ) such that a central region of the rear opening  7104  remains uncovered. In some embodiments, the badge  7114  is permanently affixed to body  7106 , while in other embodiments the badge  7114  is selectively removable. Embodiments including the selectively removable badge  7114  can provide a user more flexibility in customizing the type and volume of filler material  7192  deposited within the partial back cavity  7102 . Other embodiments of the club head  7100  do not include the badge ( FIG.  59 D ), such that the rear opening  7104  remains uncovered. 
     In some embodiments, the body  7106  is formed from 17-4 stainless steel. In other embodiments, the body  7106  can be formed from titanium, aluminum, another steel alloy (e.g. 455 steel, 475 steel, 431 steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, the body  7106  can be formed from carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. 
     The faceplate  7108  is formed from C300 steel. In other embodiments, the faceplate  108  can be formed from stainless steel, titanium, aluminum, another steel alloy (e.g. 455 steel, 475 steel, 431 steel, 17-4 stainless steel, maraging steel), a titanium alloy (e.g. Ti 7-4, Ti 6-4, T-9S, Ti SSAT2041, Ti SP700, Ti 15-0-3, Ti 15-5-3, Ti 3-8-6-4-4, Ti 10-2-3, Ti 15-3-3-3, Ti-6-6-2, Ti-185, or any combination thereof), an aluminum alloy, or a composite material. In other embodiments, the faceplate  108  can be formed from carpenter grade 455 steel, carpenter grade 475 steel, C300 steel, C350 steel, a Ni—Co—Cr steel alloy, a quench and tempered steel alloy, or 565 steel. In the disclosed embodiment, the body  7106  is formed from a different material than the faceplate  7108 . In other embodiments, the body  7106  can be formed from the same material as the faceplate  7108 . 
     In some embodiments, the badge  7114  is formed from aluminum. In other embodiments, the badge  7114  can be formed from other metals (e.g., titanium, metal alloys, etc.), or non-metals (e.g. polymers, elastomers, composites, wood, etc.). The material forming the badge  7114  has a lower density than that of the material forming the body  7106 , resulting in relatively more perimeter weighting of the club head  7100  as compared to that of prior-art iron-type club heads. The material forming the badge  7114  can have a specific gravity between approximately 0.1 and 8.0. 
     The body  7106  is formed by casting. The front and rear openings  7128 ,  7104  of the body  7106  simplify the casting process by reducing tight contours and eliminating undercuts and similar geometries. The faceplate  7108  can be cast, stamped (punched), machined, or otherwise formed. The badge  7114  can be cast, molded, or stamped. During manufacturing of the club head  7100 , the faceplate  7108  is swedged or welded onto the body  7106 . The damping layer  7190  and the filler material  7192  are inserted, injected, sprayed, or otherwise deposited into the partial back cavity  7102  via the rear opening  7104 , and then the badge  7114  is subsequently adhered, welded, snap-fit, or otherwise secured to the body  7106  to cover the rear opening  7104 . Other stages, such as polishing or painting, can also be performed as part of the manufacturing process. 
     The golf club heads with energy storage characteristics discussed herein may be implemented in a variety of embodiments, and the foregoing discussion of these embodiments does not necessarily represent a complete description of all possible embodiments. Rather, the detailed description of the drawings, and the drawings themselves, disclose at least one preferred embodiment of golf club heads with energy storage characteristics, and may disclose alternative embodiments of golf club heads with tiered internal thin sections. 
     EXAMPLES 
     Example 1: Cavity Back vs. Hollow Body/Inflection Point Golf Club 
     Referring to Table 1 below, the exemplary club head  3700  being a hollow bodied iron club head with an inflection point  3986  was compared to two control club head (hereafter “Control 1” and “Control 2”). Control 1 and Control 2 were cavity back iron club heads that were similar in size and loft angle to exemplary club head  3700 , but were devoid of an inflection point. Control 2 has a more pronounced cavity and wider sole than Control 1. Ball speed (measured in mph), launch angle (measured in degrees), carry distance (measured in yards), and spin rate (measured in rpm) were measured between the exemplary club head  3700 , Control 1, and Control 2. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Performance of Club Head 3700 vs. Control Club Heads 1 and 2 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Average 
               
               
                   
                 Average 
                 Average 
                 Average 
                 Carry 
               
               
                   
                 Ball Speed 
                 Launch Angle 
                 Spin Rate 
                 Distance 
               
               
                   
                 (mph) 
                 (degrees) 
                 (rpm) 
                 (yards) 
               
               
                   
               
               
                 Club Head 3700 
                 127.3 
                 15.9 
                 5931 
                 193 
               
               
                 Control 1 
                 127.6 
                 15.4 
                 5972 
                 190 
               
               
                 Control 2 
                 126.3 
                 15.8 
                 6551 
                 185 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the exemplary club head  3700  having a hollow body and inflection point  3986  produced an average ball speed of 127.3 mph, an average launch angle of 15.9 degrees, an average carry distance of 193 yards, and an average spin rate of 5931 rpm. Comparatively, Control 1 produced an average ball speed of 127.6 mph, an average launch angle of 15.4 degrees, an average carry distance of 190 yards, and an average spin rate of 5972 rpm, and Control 2 produced an average ball speed of 126.3 mph, an average launch angle of 15.8 degrees, an average carry distance of 185 yards, and an average spin rate of 6551 rpm. Although the exemplary club head  3700  experienced a decrease of about 0.2% in average ball speed compared to Control 1 and an increase of about 0.8% to 1% in average ball speed compared to Control 2, the average launch angle and average spin rate increased the average carry distance farther due to the hollow body and inflection point  3986  of the exemplary club head  3700 . The exemplary club head  3700  experienced a 3.25% increase in the average launch angle compared to Control 1, and a 0.6% to 1% increase in the average launch angle compared to the Control 2 respectively. Further, the exemplary club head  3700  experienced around a 0.7% decrease in average spin rate compared to Control 1 and a 9.46% decrease in average spin rate compared to Control 2 respectively. The increased average launch angle and decreased average spin rate of the exemplary club head  3700  compared to the Control 1 and 2 increased the carry distance of the ball during impact. More specifically, the exemplary club head  3700  experienced a 1.58% compared to Control 1 and 4.32% increase in average carry distance of the ball compared to Control 1 and Control 2. Therefore, the hollow body and inflection point  3986  of the exemplary club head  3700  increases the bending of the strikeface  3712  to produce optimal ball performance characteristic compared to similar sized club heads devoid of an inflection point. 
     Example 2: Cavity Back vs. Hollow Body/Inflection Point Golf Club 
     Referring to Table 2 below, the exemplary club head  4400  being a hollow bodied iron club head with an inflection point  4686  that is 55% from the top rail apex to the inflection point of the club head  4400  was compared to a control club head (hereafter “Control Club Head”). Control Club Head was a cavity back iron club head similar in size and loft angle to exemplary club head  4400 , but devoid of an inflection point and hollow body. Similar to Table 1 above, the parameters measured to compare the exemplary club head  4400  and the Control Club Head were as follows: ball speed (measured in mph), launch angle (measured in degrees), carry distance (measured in yards), and spin rate (measured in rpm). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Performance of Club Head 4400 vs. Control Club Head 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Average 
               
               
                   
                 Average 
                 Average 
                 Average 
                 Carry 
               
               
                   
                 Ball Speed 
                 Launch Angle 
                 Spin Rate 
                 Distance 
               
               
                   
                 (mph) 
                 (degrees) 
                 (rpm) 
                 (yards) 
               
               
                   
               
               
                 Club Head 4400 
                 123.8 
                 16.8 
                 6211 
                 179.2 
               
               
                 Control 1 
                 123.3 
                 16.1 
                 6746 
                 175.7 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, the exemplary club head  4400  having a hollow body and inflection point  4686  produced an average ball speed of 123.8 mph, an average launch angle of 16.8 degrees, an average carry distance of 179.2 yards, and an average spin rate of 6211 rpm, compared to the Control Club Head which produced an average ball speed of 123.3 mph, an average launch angle of 16.1 degrees, an average carry distance of 175.7 yards, and an average spin rate of 6746 rpm. The exemplary club head  4400  experienced a 0.5-1% increase in ball speed compared to the Control Club Head, but due to the hollow body and inflection point  4686  which increased the bending of the strikeface  4412 , the exemplary club head  4400  experienced a 4.35% increase in the launch angle and a 7.93% decrease in the spin rate. Because of the 4.35% increase in the launch angle and 7.93% decrease in spin rate, the exemplary club head  4400  experienced an increase of around 2% of the carry distance farther than the Control Club Head. Therefore, this increase in bending of the strikeface  4412  due to the hollow body and inflection  4686  of the exemplary club head  4400  allows for farther carry distances of the ball compared to club head similar in size, devoid of an inflection point. 
     Example 3: Smaller Volume Hollow Body Irons vs. Hollow Body Crossover 
     Referring to Table 3 below, the exemplary club head  3700 , and exemplary club head  4400  were compared to exemplary club head  2700 . All three exemplary club heads  3700 ,  4400 , and  2700  had similar loft angles and comprised a hollow body, and an inflection point. Exemplary club heads  3700  and  4400  are both significantly smaller in size (volume ranging from 0.65 inch 3  to 1.70 inches 3 ) than the exemplary club head  2700  (volume around 1.75 inches 3 ). Similar to Table 1 and Table 2 above, the parameters measured for the exemplary club heads  3700 ,  4400 , and  2700  are ball speed (measured in mph), launch angle (measured in degrees), carry distance (measured in yards), and spin rate (measured in rpm). 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Performance of Club Head 3700 and 
               
               
                 Club Head 400 vs. Club Head 2700 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Average 
               
               
                   
                 Average 
                 Average 
                 Average 
                 Carry 
               
               
                   
                 Ball Speed 
                 Launch Angle 
                 Spin Rate 
                 Distance 
               
               
                   
                 (mph) 
                 (degrees) 
                 (rpm) 
                 (yards) 
               
               
                   
               
               
                 Club Head 3700 
                 138.8 
                 12.2 
                 4322 
                 219 
               
               
                 Club Head 4400 
                 138.0 
                 11.4 
                 4135 
                 216 
               
               
                 Club Head 2700 
                 139.3 
                 11.8 
                 4312 
                 217 
               
               
                   
               
            
           
         
       
     
     As shown in Table 3, the exemplary club head  3700  produced an average ball speed of 138.8 mph, an average launch angle of 12.2 degrees, an average spin rate of 4322 rpm, and an average carry distance of 219 yards; the exemplary club head  4400  produced an average ball speed of 138.0 mph, an average launch angle of 11.4 degrees, an average spin rate of 4135 rpm, and an average carry distance of 216 yards; and the exemplary club head  2700  produced an average ball speed of 139.3 mph, an average launch angle of 11.8 degrees, an average spin rate of 4312 rpm, and an average carry distance of 217 yards. The exemplary club head  3700  experienced a 0.92% increase in carry distance over the exemplary club had 2700, while the exemplary club head  4400  experienced a 0.46% decrease in carry distance compared to the exemplary club had 2700. The small percent difference of the carry distance of the ball between the exemplary club heads  3700 ,  4400 , and  2700 , were indicative to the bending of the strikeface due to the hollow body and inflection points, regardless of the significantly smaller sizes of the exemplary club head  3700  and exemplary club head  4400 . Because of the smaller size and lower inflection point, the exemplary club heads  3700  and  4400  allows a player the benefit of the look and feel of a smaller iron body club head, with the ball performance results (e.g., launch angle, carry distance) of a higher volume sized hollow body club head with a higher inflection point (i.e., exemplary club head  2700 ). 
     Example 4: Cavity Back vs. Hollow Body/Inflection Point Golf Club 
     Referring to Table 4 below, the exemplary club head  4900  is a hollow bodied iron club head with an inflection point  5186  located roughly 52% below the top rail apex. The club head  4900  was compared to a control club head (hereafter “Control Club Head”). Control Club Head was a cavity back iron club head similar in size to exemplary club head  4900 , but devoid of an inflection point and hollow body. The Control Club Head comprised a loft angle roughly 1° lower than the exemplary club head  4900 . Similar to Table 1 above, the parameters measured to compare the exemplary club head  4900  and the Control Club Head were as follows: ball speed (measured in mph), launch angle (measured in degrees), carry distance (measured in yards), and spin rate (measured in rpm). 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Performance of Club Head 4900 vs. Control Club Head 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Average 
               
               
                   
                 Average 
                 Average 
                 Average 
                 Carry 
               
               
                   
                 Ball Speed 
                 Launch Angle 
                 Spin Rate 
                 Distance 
               
               
                   
                 (mph) 
                 (degrees) 
                 (rpm) 
                 (yards) 
               
               
                   
               
               
                 Club Head 4900 
                 145.1 
                 11.6 
                 3980 
                 229 
               
               
                 Control 1 
                 146.1 
                 11.1 
                 4073 
                 227 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, the exemplary club head  4900  having a hollow body and inflection point  5186  produced an average ball speed of 145.1 mph, an average launch angle of 11.6 degrees, an average carry distance of 229 yards, and an average spin rate of 3980 rpm, compared to the Control Club Head which produced an average ball speed of 146.1 mph, an average launch angle of 11.1 degrees, an average carry distance of 227 yards, and an average spin rate of 4073 rpm. 
     The higher launch angle of the club head  4900  results from its higher loft angle. The lower ball speed can also be expected due to the higher loft angle of the club head  4900 . The unexpected result is in the spin rate of the club head  4900  versus the spin rate of the Control Club Head. One of skill in the art would expect the spin rate of the higher-lofted club head (in this example the club head  4900 ) to be significantly greater than the spin rate of the lower-lofted club head (in this example the Control Club Head). However, the measured spin rates are close to each other, to the extent that in the measured data, the error bars of the spin rates overlap. The spin rates of the club head  4900  and the Control Club Head are not significantly different. Thus, this test shows that the golf club head  4900  exhibits lower spin rates than the Control Club Head for a given loft angle. This lower spin rate reduces the ballooning of the golf ball during flight. Golf balls that are imparted a high spin rate upon impact tend to twist upwards, or balloon, during flight. This dynamic increase in the flight trajectory height of the golf ball can adversely affect the carry distance and result in unpredictable shots. The average carry distance for the exemplary golf club  4900  is roughly the same as the average carry distance of the Control Club Head. The inflection point  5186  of the exemplary club head  4900  along with the hollow body allow the faceplate  4912  to bend in a manner that reduces the spin imparted to the golf ball. 
     In addition to the data in Table 4 above, the test revealed an average statistical plot area within which the test shots landed. The average statistical plot area for the exemplary club head  4900  was 6.2% smaller than the average statistical plot area for the Control Club Head. This shows that the exemplary club head  4900  demonstrated higher precision than the Control Club Head. Therefore, the hinging of the faceplate  4912  about the inflection point  5186  does not adversely affect the golfer&#39;s ability to control their shots. Rather, the golfer&#39;s shot precision is increased. 
     Replacement of one or more claimed elements constitutes reconstruction and not repair. Additionally, benefits, other advantages, and solutions to problems have been described with regard to specific embodiments. The benefits, advantages, solutions to problems, and any element or elements that may cause any benefit, advantage, or solution to occur or become more pronounced, however, are not to be construed as critical, required, or essential features or elements of any or all of the claims, unless such benefits, advantages, solutions, or elements are expressly stated in such claims. 
     As the rules to golf may change from time to time (e.g., new regulations may be adopted or old rules may be eliminated or modified by golf standard organizations and/or governing bodies such as the United States Golf Association (USGA), the Royal and Ancient Golf Club of St. Andrews (R&amp;A), etc.), golf equipment related to the apparatus, methods, and articles of manufacture described herein may be conforming or non-conforming to the rules of golf at any particular time. Accordingly, golf equipment related to the apparatus, methods, and articles of manufacture described herein may be advertised, offered for sale, and/or sold as conforming or non-conforming golf equipment. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     While the above examples may be described in connection with a driver-type golf club, the apparatus, methods, and articles of manufacture described herein may be applicable to other types of golf club such as a fairway wood-type golf club, a hybrid-type golf club, an iron-type golf club, a wedge-type golf club, or a putter-type golf club. Alternatively, the apparatus, methods, and articles of manufacture described herein may be applicable to other type of sports equipment such as a hockey stick, a tennis racket, a fishing pole, a ski pole, etc. 
     Moreover, embodiments and limitations disclosed herein are not dedicated to the public under the doctrine of dedication if the embodiments and/or limitations: (1) are not expressly claimed in the claims; and (2) are or are potentially equivalents of express elements and/or limitations in the claims under the doctrine of equivalents.