Golf club head with an improved striking face

Abstract

To design a striking face which can improve performance, where the striking face is a very important area in golf club design because the striking face is the portion of a golf club head that interacts with a golf ball at impact and influences the ball's trajectory, speed and spin, where all of these parameters are important for a golfer as they influence the ball's travel distance and flight shape.SOLUTION: A golf club head having an improved striking face 102 is disclosed herein. More specifically, the golf club head in accordance with the present invention has a striking face including a thin center zone and multiple zones surrounding the center zone.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] This invention generally relates to a golf club head having an improved striking face. More specifically, a golf club head according to this invention is composed of a striking face portion having a plurality of regions. Each region has a different thickness profile to improve the COR.

Background Art

[0002] The design of modern golf clubs has evolved since the early days of golf. The benefit of every technological advancement in golf club technology is that golf has become easier to play for golfers of all levels. However, these advancements pose significant challenges for golf club engineers.

[0003] In the design of golf clubs, the striking face is a very important part. The striking face is the part of the golf club head that interacts with the golf ball at impact and affects the ball's trajectory, speed, and spin. All of these parameters are important for golfers because they all affect the distance the ball travels and its flight shape. Therefore, there is a strong demand for a design of the striking face that improves performance.

[0004] U.S. Patent No. 6,605,007, such as Bissonnette, defines a golf club having a variable face thickness. The face is composed of a center zone between 15% and 60% of the total area of the striking face. The center zone is surrounded by a peripheral zone, and the center zone has a significantly higher flexural rigidity than the peripheral zone.

[0005] Similarly, U.S. Patent No. 6,904,663 by Willett et al. defines a golf club with considerable thickness variation. This thickness variation is achieved by machining the striking face so that it has a small center recess that is about the same thickness as the top recess, and the heel and toe are the thinnest parts. The thickest part of the face surrounds the small center recess. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 6605007 [Patent Document 2] U.S. Patent No. 6904663 [Overview of the project]

[0007] One aspect of this invention is a golf club having a golf club head, a grip, and a shaft between them, wherein the golf club head has improved COR and feel. The golf club head preferably consists of a striking face portion located at the front and a body portion attached to the striking face portion and forming a cavity between them. The striking face consists of a thin center zone and a plurality of variable-thickness zones surrounding the center zone.

[0008] Another embodiment of this invention has an iron-type golf club comprising a club head, a grip, and a shaft between them. The golf club head consists of a striking face portion located at the front of the club head, a hosel that houses the shaft, and a body portion having a topline that crosses the top of the club head, a toe portion at the bottom of the club head, a heel portion, and a sole portion. The striking face portion has a striking face area and a center zone that surrounds the center of the face of the striking face portion. The center zone has a substantially uniform thickness, and the area of ​​the center zone is between approximately 15% and 30% of the striking face area. Multiple perimeter zones extend between the center zone and the perimeter of the club head, with the thickness of the portion adjacent to the center zone being minimal and the thickness of the portion adjacent to the perimeter of the club head increasing continuously to the maximum. Preferably, the thickness of the perimeter zones increases linearly with a slope of about 1° to 5°. Preferably, the thickness of the center zone is less than 2 mm, and the mass of the striking face portion is greater than 54 grams.

[0009] One aspect of this invention is an iron-type golf club including a golf club head, grip, and shaft between them, wherein the golf club head has improved COR and feel. The golf club head preferably consists of a striking face portion located at the front and a body portion attached to the striking face portion and forming a cavity between them. The golf club head comprises a top line, sole, toe portion, heel portion, and hosel. In this invention, the striking face portion preferably comprises nine zones, including a center zone, upper center zone, lower center zone, upper heel zone, heel center zone, lower heel zone, upper toe zone, toe center zone, and lower toe zone. The center zone includes the face center and preferably comprises the minimum thickness of the striking face.

[0010] Another preferred embodiment of this invention is an iron-type golf club comprising a golf club head, grip, and shaft between them, wherein the golf club head has an improved striking face comprising a center zone, an upper center zone, a lower center zone, an upper heel zone, a heel center zone, a lower heel zone, an upper toe zone, a toe center zone, and a lower toe zone. The center zone includes the face center, has the minimum face thickness, and comprises about 10% to 40% of the total striking face area. Furthermore, the center zone is preferably of a constant thickness and forms a quadrilateral. Even more preferably, the center zone is a parallelogram, and most preferably a rectangle.

[0011] Another preferred embodiment of this invention is an iron-type golf club including a club head, a grip, and a shaft between them. The golf club head consists of a striking face portion located at the front of the club head, and a body portion having a hosel for housing the shaft, a topline running across the top of the club head, a toe portion at the bottom of the club head, a heel portion, and a sole portion. The improved striking face portion has a striking face area and has nine zones, including a center zone surrounding the center of the face of the striking face portion, an upper center zone located between the center zone and the topline, a lower center zone located between the center zone and the sole, a heel center zone located between the center zone and the heel portion, an upper heel zone located between the heel center zone and the topline, a lower heel zone located between the heel center zone and the sole, a toe center zone located between the center zone and the toe portion, an upper toe zone located between the toe center zone and the topline, and a lower toe zone located between the toe center zone and the sole. The center zone has a substantially uniform thickness t1, and the center zone area A1 is approximately 15% to 35% of the hitting face area. Preferably, the center zone area is the largest of all nine zones. The upper center zone preferably has a variable thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t2 adjacent to the top line. The lower center zone preferably has a variable thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t3 adjacent to the sole. The heel center zone preferably has a variable thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t4 adjacent to the heel portion. The lower heel zone preferably has a variable thickness that increases from a minimum thickness t1 adjacent to the center zone and heel center zone to a maximum thickness t6 adjacent to the sole. The toe center zone preferably has a variable thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t7 adjacent to the toe portion.The upper toe zone preferably has a variable thickness that increases from a minimum thickness t1 at points adjacent to the center zone and toe center zone to a maximum thickness t8 near the top line, and the lower toe zone preferably has a variable thickness that increases from a minimum thickness t1 at points adjacent to the center zone and toe center zone to a maximum thickness t9 near the sole. Preferably, the maximum thickness t8 of the upper toe zone is the maximum thickness at the striking face.

[0012] In preferred embodiments, the central thickness t1 is less than 2.2 mm, more preferably about 1.5 mm to 2.0 mm, and the center zone has a substantially quadrilateral perimeter. More preferably, the center zone has a substantially rectangular perimeter. Preferably, the minimum thickness t1 of the striking face is less than 60% of the maximum thickness t8 of the striking face. Even more preferably, the minimum thickness t1 of the striking face is less than 80% of the thickness of the striking face at the heel portion t4. Even more preferably, the thickness of the striking face at the top line t2 is at least 25% greater than the minimum thickness t1 of the striking face.

[0013] In a preferred embodiment of this invention, the thickness of the center zone is substantially constant, and the thicknesses of all other zones are variable, increasing in constant proportion from the center zone. For example, the thickness of the lower center zone increases continuously from t1 to t3, where t3 is at least 10% greater than t1, and the thickness of the heel center zone increases continuously from t1 to t4. Similarly, the thickness of the upper heel zone increases continuously from t1 to t5, and the thickness of the lower heel zone increases continuously from t1 to t6. The thickness of the toe center zone also increases continuously from a minimum thickness t1 to a maximum thickness t7. The thickness of the upper toe zone increases continuously from t1 to t8, and the thickness of the lower toe zone increases continuously from t1 to t9.

[0014] In one embodiment of this invention, the center zone has a center zone area A1 that is approximately 15% to 35% of the hitting face area. Preferably, the center zone has a center zone area A1 that is larger than the toe upper zone area A8, and the toe upper area A8 is approximately 10% to 30% of the hitting face area. Furthermore, the center zone has a center zone area A1 that is larger than the toe center zone area A7, and the toe center area A7 is approximately 10% to 30% of the hitting face area.

[0015] Another preferred embodiment of this invention is an iron-type golf club having a club head, a grip, and a shaft between them. The golf club head consists of a striking face portion located at the front of the club head, a hosel that houses the shaft, and a body portion having a top line that crosses the top of the club head, a toe portion at the bottom of the club head, a heel portion, and a sole portion. The striking face portion has a striking face area and has nine zones, including a center zone surrounding the center of the face of the striking face portion, an upper center zone located between the center zone and the top line, a lower center zone located between the center zone and the sole, a heel center zone located between the center zone and the heel portion, an upper heel zone located between the heel center zone and the top line, a lower heel zone located between the heel center zone and the sole, a toe center zone located between the center zone and the toe portion, an upper toe zone located between the toe center zone and the top line, and a lower toe zone located between the toe center zone and the sole. The center zone has a substantially uniform thickness t1, and the center zone area A1 is approximately 15% to 35% of the hitting face area. [Brief explanation of the drawing]

[0016] The foregoing and other features and advantages of the present invention will become apparent from the following description of the present invention, as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the present invention and to enable a person skilled in the relevant art to practice and use the present invention.

[0017] The foregoing and other features and advantages of the present invention will become apparent from the following description of the present invention shown in the accompanying drawings. The accompanying drawings, which are incorporated herein and constitute a part of the specification, further explain the principles of the present invention and enable a person skilled in the relevant art to manufacture and use the present invention. [Figure 1] FIG. 1 of the accompanying drawings shows a front perspective view of a golf club head according to an embodiment of the present invention. [Figure 2] FIG. 2 of the accompanying drawings shows a rear perspective view of the golf club disclosed in FIG. 1. [Figure 3] FIG. 3 of the accompanying drawings shows a rear view of the striking face of a club head according to an embodiment of the present invention. [Figure 4] FIG. 4 of the accompanying drawings shows a rear view of the striking face of FIG. 3 and shows a cross-sectional view of the striking face. [Figure 5] FIG. 5 of the accompanying drawings shows a horizontal cross-sectional view of the upper portion of the striking face of FIG. 3. [Figure 6] FIG. 6 of the accompanying drawings shows a horizontal cross-sectional view of the horizontal center portion of the striking face of FIG. 3. [Figure 7] FIG. 7 of the accompanying drawings shows a horizontal cross-sectional view of the lower portion of the striking face of FIG. 3. [Figure 8] FIG. 8 of the accompanying drawings shows a longitudinal cross-sectional view of the heel portion of the striking face of FIG. 3. [Figure 9] FIG. 9 of the accompanying drawings shows a vertical cross-sectional view of the vertical center portion of the striking face of FIG. 3. [Figure 10] FIG. 10 of the accompanying drawings shows a longitudinal cross-sectional view of the toe portion of the striking face of FIG. 3. Detailed Description of the Invention

[0018] The following detailed description describes the presently contemplated best mode for carrying out the invention. This description is not intended to limit the invention and is provided solely for the purpose of explaining the general principles of the invention. The scope of the invention is best defined by the appended claims. Although various features of the invention are described below, each may be used independently or in combination with other features.

[0019] Figures 1-2 of the accompanying drawings show a golf club head 100 according to an exemplary embodiment of the invention. The golf club head 100 shown herein includes a striking face portion 102 and a rear body portion or body portion 104 including a topline portion 112, a toe portion 114, a sole portion 116, a heel portion 118, and a hosel 120. The hosel 120 is configured to receive the tip end of a golf shaft not shown. The butt end of the golf shaft is configured to receive a golf grip not shown. The golf club head 100 shown herein includes an optional back plate 122 such that the golf club head 100 is hollow.

[0020] The striking face portion 102 shown in FIG. 1 includes a generally planar outer front face portion 124 including a face center FC and a return portion 126 forming a leading edge LE and a front portion of the sole portion 116. The striking face portion 102 preferably has a face center thickness of less than 2 mm and an overall mass of more than 54 grams.

[0021] As shown in Figure 3, the striking face portion 102 preferably comprises a non-planar back surface 130, thereby comprising nine zones including a center zone 132, an upper center zone 134, a lower center zone 136, an upper heel zone 138, a heel center zone 140, a lower heel zone 142, an upper toe zone 144, a toe center zone 146, and a lower toe zone 148. The striking face portion 102 also includes an outer perimeter 150, which is welded to the topline portion 112, the toe portion 114, and the heel portion 118. The return portion 126 of the striking face portion 102 is also welded to the sole portion 116 to form its front and leading edge LE. Figure 3 also discloses the vertical y and horizontal x directions for reference.

[0022] The center zone 132 includes the face center FC and preferably comprises the minimum thickness t1 of the striking face. Preferably, the center zone 132 comprises a substantially uniform thickness t1, and the center zone area A1 is between approximately 15% and 35% of the striking face area, which is the planar region shown inside around the striking face portion 102 in Figures 3 and 4. Preferably, the center zone area A1 is the largest area among all nine zones. The upper center zone 134 preferably comprises a variable thickness that increases from the minimum thickness t1 adjacent to the center zone 132 to the maximum thickness t2 adjacent to the topline portion 112. The lower center zone 136 preferably comprises a variable thickness that increases from the minimum thickness t1 adjacent to the center zone 132 to the maximum thickness t3 adjacent to the sole portion 116. The heel center zone preferably comprises a variable thickness that increases from the minimum thickness t1 adjacent to the center zone 132 to the maximum thickness t4 adjacent to the heel portion 118. The lower heel zone preferably has a variable thickness that increases from a minimum thickness t1 at points adjacent to the center zone 132 and heel center zone 140 to a maximum thickness t6 adjacent to the sole portion 116. The toe center zone 146 preferably has a variable thickness that increases from a minimum thickness t1 adjacent to the center zone 132 to a maximum thickness t7 adjacent to the toe portion 114. The maximum thickness t8 of the upper toe zone preferably has the greatest thickness on the striking face portion 102. The upper toe zone 144 preferably has a variable thickness that increases from a minimum thickness t1 at points adjacent to the center zone 132 and toe center zone 146 to a maximum thickness t8 near the topline portion 112, and the lower toe zone 148 preferably has a variable thickness that increases from a minimum thickness t1 at points adjacent to the center zone 132 and toe center zone 146 to a maximum thickness t9 near the sole portion 116.

[0023] Preferably, as shown in Figures 4-10, the upper center zone 134 has a variable thickness that increases continuously from a minimum thickness t1 to a maximum thickness t2. More preferably, the upper center zone 134 has a variable thickness that increases linearly and continuously from a minimum thickness t1 to a maximum thickness t2, with an angle α of 3° to 5°. The lower center zone 136 preferably has a variable thickness that increases continuously from a minimum thickness t1 to a maximum thickness t3. More preferably, the lower center zone 136 has a variable thickness that increases linearly and continuously from a minimum thickness t1 to a maximum thickness t3, where the angle α2 is between 3° and 5°. The heel center zone preferably has a variable thickness that increases linearly and continuously from a minimum thickness t1 to a maximum thickness t4. More preferably, the heel center zone 140 has a variable thickness that increases linearly and continuously from a minimum thickness t1 to a maximum thickness t4, where the angle α3 is between 3° and 5°. The toe center zone 146 preferably has a variable thickness that increases continuously from a minimum thickness t1 to a maximum thickness t7 adjacent to the center zone 132, where the angle α4 is between approximately 3° and 7° and greater than α3. The toe upper zone 144 preferably has a variable thickness that increases vertically toward the topline portion 112 at an angle α6 of approximately 1° to 4°, and the toe lower zone 148 has a variable thickness that increases horizontally toward the toe portion 114 at an angle α5 of approximately 1° to 4°.

[0024] Preferably, the center zone 132 surrounds the projection of the face center FC, allowing the face center FC of the outer front face portion 124 to flex upon impact, thereby improving the overall impact face COR. In a preferred embodiment, the thickness t1 is approximately 1.5mm to 2.0mm, t2 is 2.2mm to 2.9mm, t3 is 2.0mm to 2.5mm, t4 is 2.3mm to 3.0mm, t5 is 2.1mm to 2.5mm, t6 is 2.7mm to 3.2mm, t7 is 3.0mm to 3.5mm, t8 is 3.0mm to 3.6mm, and t9 is 2.8mm to 3.2mm. Preferably, t8>t7>t9>t6>t4>t5>t2>t3>t1. Furthermore, preferably, t8 is at least 50% greater than t1, t7 is at least 40% greater than t1, t2 is at least 25% greater than t1, and t3 is at least 10% greater than t1. Similarly, t1 is less than 60% of t8, less than 65% of t7, and less than 80% of t4.

[0025] The outer front face portion 124 is preferably made of steel and is positioned on the outer front portion of the striking face portion 102. The outer front face portion 124 is a substantially flat outer surface including a plurality of grooves 128. More preferably, the outer front face portion 124 is made of high-strength steel with a maximum tensile strength exceeding 2000 MPa, and even more preferably exceeding 2300 MPa. Most preferably, the outer front face portion 124 is made from AerMet340 or the like. This thin outer front face portion 124 and its high strength contribute to the formation of a high COR of the golf club head 100.

[0026] In a preferred high-COR embodiment of this invention, the center zone comprises a center zone area A1 which is approximately 15% to 35% of the striking face area, i.e., the planar area shown inside the periphery of the striking face portion 102 in Figures 3 and 4. Preferably, the center zone area A1 is larger than the toe upper zone area A8 and is approximately 10% to 30% of the striking face area. Furthermore, the center zone area A1 is larger than the toe center zone area A7 and is approximately 10% to 30% of the striking face area. Preferably, the center zone area A1 is the largest area, the upper center zone area A2 and lower center zone area A3 are 5% to 15% of the striking face area, and the heel center zone area A4 is 10% to 20% of the striking face area. Furthermore, the area of ​​the horizontal center portion of the face (A1+A7+A4) is greater than the sum of the areas of the horizontal upper portion of the face (A2+A8+A5) and the horizontal lower portion of the face (A3+A6+A9). In other words, the following equation is satisfied: a.(A1+A7+A4)>(A2+A8+A5)+(A3+A6+A9) Preferably, the area of ​​the horizontal center portion of the face (A1 + A7 + A4) is greater than 50% of the impact face area.

[0027] Except for the examples of operation, or unless explicitly specified, all numerical ranges, quantities, values, and percentages in the preceding sections of the specification, such as the quantity of material, moment of inertia, center of gravity, loft, draft angle, and various performance ratios, can be read as if they were preceded by the word "approximately," even if the word "approximately" does not explicitly appear in the value, quantity, or range. Therefore, unless otherwise indicated, the numerical parameters described in the preceding specification and the appended claims are approximations that may vary depending on the desired properties to be obtained by this invention. At the very least, each numerical parameter should be interpreted using ordinary rounding techniques, taking into account the reported number of significant figures, and not as an attempt to limit the application of the doctrine of equivalents to the claims.

[0028] Although the numerical ranges and parameters representing the broad scope of this invention are approximations, the numerical values ​​shown in specific examples are reported as accurately as possible. However, any numerical value inherently contains a certain degree of error that inevitably arises from the standard deviation observed in each test measurement. Furthermore, where various ranges of numerical values ​​are shown here, it is assumed that any combination of these values, including the listed values, may be used.

[0029] Of course, the foregoing relates to exemplary embodiments of the invention and should be understood that modifications are possible without departing from the spirit and scope of the invention as described in the following claims. For example, the examples of the invention described above refer to a nearly rectangular center zone 132, but it is clear that many of the objectives of the invention can be satisfied by changing the shape of the center zone 132 to a different polygonal or elliptical zone.

Claims

1. In iron-type golf clubs, A golf club has a head, a grip, and a shaft between them. The above-mentioned golf club head is composed of a striking face portion located at the front of the golf club head, a hosel that houses the shaft, a top line extending across the top of the golf club head, and a main body portion located at the bottom of the golf club head, having a toe portion, a heel portion, and a sole portion. The above-mentioned striking face portion has a striking face area and includes nine zones, including a center zone surrounding the center of the face portion of the striking face portion, an upper center zone located between the center zone and the top line, a lower center zone located between the center zone and the sole portion, a heel center zone located between the center zone and the heel portion, an upper heel zone located between the heel center zone and the top line, a lower heel zone located between the heel center zone and the sole portion, a toe center zone located between the center zone and the toe portion, an upper toe zone located between the toe center zone and the top line, and a lower toe zone located between the toe center zone and the sole portion. The above center zone has a substantially uniform center zone thickness t1, and the area A1 of the above center zone is approximately 15% to 35% of the above striking face area. The above upper center zone has a non-uniform thickness that increases from the minimum thickness t1 adjacent to the center zone to the maximum thickness t2 of the upper center zone adjacent to the top line. The lower center zone described above has a non-uniform thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t3 adjacent to the sole portion. The heel center zone has a non-uniform thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t4 adjacent to the heel portion. The heel lower zone has a non-uniform thickness that increases from the minimum thickness t1 at the center zone and the points adjacent to the heel center zone to the maximum thickness t6 of the heel lower zone adjacent to the sole portion. The above toe center zone has a non-uniform thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t7 adjacent to the toe portion. The above-mentioned upper toe zone has a non-uniform thickness that increases from a minimum thickness t1 at the center zone and points adjacent to the toe center zone to a maximum thickness t8 of the upper toe zone adjacent to the top line. The iron-type golf club is characterized in that the toe lower zone has a non-uniform thickness that increases from a minimum thickness t1 at a point adjacent to the center zone and the toe center zone to a maximum thickness t9 of the toe lower zone adjacent to the sole portion.

2. The golf club according to claim 1, wherein the thickness t1 of the center zone is less than 2.2 mm.

3. The golf club according to claim 1, wherein the thickness t1 of the center zone is approximately 1.5 mm to 2.0 mm, and the periphery of the center zone is substantially rectangular.

4. The golf club according to claim 3, wherein the above-mentioned center zone comprises a substantially rectangular perimeter.

5. The golf club according to claim 1, wherein the maximum thickness t2 of the upper center zone is smaller than the maximum thickness t4 of the heel center zone and the maximum thickness t7 of the toe center zone.

6. The golf club according to claim 5, wherein the thickness t1 of the center zone is less than 65% of the maximum thickness t7 of the toe center zone.

7. The golf club according to claim 5, wherein the thickness t1 of the center zone is less than 80% of the maximum thickness t4 of the heel center zone.

8. The golf club according to claim 1, wherein the thickness of the upper center zone increases continuously from t1 to t2, and t2 is at least 25% greater than t1.

9. The golf club according to claim 1, wherein the thickness of the lower center zone increases continuously from t1 to t3, and t3 is at least 10% greater than t1.

10. The golf club according to claim 1, wherein the thickness of the heel center zone increases continuously from t1 to t4.

11. The golf club according to claim 1, characterized in that the thickness of the upper heel zone increases continuously from t1 to t5.

12. The golf club according to claim 1, wherein the thickness of the lower heel zone increases continuously from t1 to t6.

13. The golf club according to claim 1, wherein the overall thickness of the toe center zone increases continuously from t1 to t7.

14. The golf club according to claim 1, wherein the thickness of the upper toe zone increases continuously from t1 to t8.

15. The golf club according to claim 1, wherein the thickness of the toe lower zone increases continuously from t1 to t9.

16. The golf club according to claim 1, wherein the thickness of the upper heel zone increases continuously from t1 to t5.

17. The golf club according to claim 1, wherein the toe upper zone has a toe upper area A8 that is approximately 10% to 30% of the striking face area.

18. The golf club according to claim 1, wherein the toe center zone comprises a toe center area A7 that is approximately 10% to 30% of the striking face area.

19. In iron-type golf clubs, A golf club has a head, a grip, and a shaft between them. The above golf club head has a striking face portion located at the front of the club head, a hosel for housing the shaft, a top line extending across the top of the club head, and a main body portion having a toe portion, a heel portion, and a sole portion at the bottom of the club head. The above-mentioned striking face portion has a striking face area and includes nine zones, including a center zone surrounding the center of the face portion of the striking face portion, an upper center zone located between the center zone and the top line, a lower center zone located between the center zone and the sole, a heel center zone located between the center zone and the heel portion, an upper heel zone located between the heel center zone and the top line, a lower heel zone located between the heel center zone and the sole, a toe center zone located between the center zone and the toe portion, an upper toe zone located between the toe center zone and the top line, and a lower toe zone located between the toe center zone and the sole. The above center zone has a center zone thickness t1 which is substantially uniform, and the area A1 of the center zone is approximately 15% to 30% of the above striking face area. The upper center zone has a non-uniform thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t2 adjacent to the top line, the area A2 of the upper center zone is between 5% and 15% of the striking face area, and the maximum thickness t2 of the upper center zone is at least 25% greater than the center zone thickness t1. The lower center zone described above has a non-uniform thickness that increases from the minimum thickness t1 adjacent to the center zone to the maximum thickness t3 of the lower center zone adjacent to the sole. The heel center zone has a non-uniform thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t4 adjacent to the heel portion. The toe center zone is characterized by having a non-uniform thickness that increases from a minimum thickness t1 adjacent to the center zone to a maximum thickness t7 adjacent to the toe portion, the area of ​​the toe center zone is between 10% and 30% of the striking face area, and the thickness t1 of the center zone is less than 65% of the maximum thickness t7 of the toe center zone.

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