Golf clubs are products subject to the equipment rules set by the R&A (Royal & Ancient Golf Club of St. Andrews) and the USGA (United States Golf Association), which impose clear upper limits on head volume, rebound performance, and moment of inertia—essentially establishing a predetermined “performance ceiling.”Nevertheless, manufacturers launch new products every year, and behind the scenes, the competition to file patents continues.In this article, using U.S. Patent No. 11,083,937 (Topgolf Callaway Brands, registered August 10, 2021)—a patent for a method of manufacturing golf club heads—as a case study, I will explain from a patent attorney’s perspective: (1) the content of the claims, (2) the patent family built through a series of continuation applications,③ the significance of the strategy to deliberately file “process claims,” ④ the relationship between the Equipment Rules and patent applications, and ⑤ the history of patent disputes in the industry and the situation facing Japanese manufacturers—from the perspective of a patent attorney.
Table of Contents
U.S. Patent No. 11,083,937 B2, “Method of Manufacturing a Golf Club Head Having Stress-Reducing Features,” was filed on January 14, 2020, and granted on August 10, 2021.with a priority date of June 30, 2015, a term expiring on October 2, 2035, and a status listed as “Active” (verified on Google Patents; status may change due to annuity payments, etc.).The core of the technology involves placing a reinforcing plate inside the hollow club head, behind the striking face, to connect the crown (top) and sole (bottom), thereby dispersing the stress concentrated around the face upon ball impact while minimizing the increase in mass.
It is noteworthy that this patent claims a manufacturing method rather than the structure of the finished product. Here is a quote from the original text of Claim 1:
"A method comprising the steps of: preparing a wax mold of a golf club head body, the wax mold of the golf club head body comprising a striking face section, a sole section extending from a lower edge of the striking face section, and a return section extending from an upper edge of the striking face section, ... the return section comprising an elongated through-hole, and the sole section comprising an elongated receiving pocket; preparing a wax mold of a plate comprising an upper end and a lower end; inserting the plate into the elongated through-hole and seating the lower end in the elongated receiving pocket; bonding the plate to the body with an adhesive material to form a combined wax mold; and casting a golf club head from the combined wax mold, wherein the through-hole is aligned with the receiving pocket, wherein the plate has a variable thickness ranging from 0.020 inch to 0.160 inch, wherein the plate is located within 1 inch of a rear surface of the striking face section ..., and wherein no portion of the plate makes contact with the striking face section."
Source: Google Patents (US11083937B2) Claim 1 (omissions by the author; please refer to the original text for the full version)
To summarize in Japanese: ① Prepare a wax pattern (the lost pattern for lost-wax casting) of the head body—the body consists of a striking face section, a sole section, and a return section, with an elongated through-hole in the return section and a receiving pocket in the sole section; ② Prepare a wax pattern of the plate;③ Insert the plate into the through-hole and seat its lower end in the pocket; ④ Bond it to the main body using an adhesive to form a single, integrated wax pattern; ⑤ Cast the head from that integrated wax pattern—these are the five steps.Furthermore, specific numerical and positional constraints are specified: (i) the plate has a variable thickness of 0.020 to 0.160 inches (approximately 0.5 to 4 mm); (ii) it is positioned within 1 inch (25.4 mm) of the back of the face; and (iii) the plate does not come into contact with the face.
What makes this patent interesting is that the unit of invention is based not on the “structure of the finished head,” but on the process of “assembling the components at the wax pattern stage and then casting them as a single unit.”Rather than retrofitting reinforcing materials through post-casting welding or machining, integrating them at the lost-wax model stage allows for the creation of complex internal structures in a single casting—insights from the manufacturing floor are directly incorporated into the claims.
This patent does not exist in isolation. Following the cross-references at the beginning of the specification reveals a long lineage of continuous-in-part (CIP) and divisional applications layered in multiple stages.
| Patent Number | Registration Date | Claim Type | Position |
|---|---|---|---|
| US 9,486,677 | November 8, 2016 | Product | First generation starting in 2015 (product claims) |
| US 9,597,558 | March 21, 2017 | Invention | Filed June 30, 2015 (Priority date for this application; claims relating to an article using a composite tube) |
| US 9,931,550 | April 3, 2018 | Method | Beginning of the manufacturing method claim generation (wax pattern → casting) |
| US 10,532,258 | January 14, 2020 | Product | Secured product claims by splitting off from a method patent (US 10,335,647) |
| US 11,083,937 | August 10, 2021 | Method | Subject of this article (CIP of the US 10,532,258 family) |
| US 11,433,282 | September 6, 2022 | Method | Continuation of This Application |
| US 12,102,891 | October 1, 2024 | Method | Latest Generation in the Family |
If we trace the family’s lineage further back, the earliest priority basis dates back to a provisional application filed on June 27, 2012 (US61/665,203).In other words, over the course of more than 10 years, this patent family has continued to secure claims for “articles” and “methods” alternately through a series of continuation, divisional, and CIP applications.A CIP (Continuing-in-Part) application is a system unique to the U.S. that allows for the addition of new matter; since the effective priority date for the added matter is the CIP filing date, the effective priority date for each claim may vary between 2012 and 2015 or later—a practical point to note when analyzing this patent family.This can be seen as an example of the same concept used in building a network of divisional applications observed in Nintendo’s game patents (see the article explaining divisional application strategies) being implemented more flexibly in the U.S. through the use of CIPs.
We have also confirmed this strategy’s extension to Japan. Patent No. 6507125, “Golf Club Head Having a Stress-Reducing Feature” (Callaway Golf Company,filed June 6, 2016; granted April 24, 2019) has been granted in Japan. Claim 1 of this patent is a product claim—not a method claim—ending with “...the aforementioned golf club head” (verified on the Google Patents page).Note that I was unable to confirm a direct Japanese corresponding publication for US11,083,937 itself (the “Corresponding Publications” column on Google Patents lists only U.S. publications).
It is a common perception in patent practice that “it is difficult to prove that a method claim is carried out within a factory, making it weak for enforcement.” Nevertheless, the fact that this patent family has accumulated multiple generations of method claims is likely due to the institutional environment of U.S. patent law.
Section 271(g) of the U.S. Patent Act defines as infringement the unauthorized importation into the United States, or the sale or use within the United States, of “a product made by a method patented in the United States” (with exceptions for cases where the product has been substantially altered in subsequent processes, etc.).This provision was newly established in 1988 to close a “loophole” whereby products were imported into the U.S. after the U.S.-patented method had been implemented abroad.Since golf club heads are often cast at specialized factories overseas, the existence of this provision—which allows a method patent to be asserted upon importation into the U.S., even if manufacturing took place outside the U.S.—underpins the effectiveness of method claims in the United States (the application of this provision to the golf club head industry described in this paragraph is a general practical classification).
In Japan, on the other hand, the effect of a patent for a “method of producing an article” extends to the transfer or import of articles produced by that method (Patent Act, Article 2, Paragraph 3, Item 3); however, it is not easy to prove that the opposing party’s product was “made by that method.”Although Article 104 of the Patent Act contains a presumption provision regarding production methods, it applies only when the produced article “was not publicly known in Japan prior to the filing of the patent application”; therefore, this presumption typically does not apply to existing product categories such as golf club heads.In the Japanese market, securing product claims defined by structure is relatively more important—a conclusion consistent with the fact that Callaway holds Japanese Patent No. 6507125, which is a product claim (though a causal relationship cannot be definitively established).
Clarification of Terminology: Claim 1 of US11,083,937 is a pure process claim in the “method” category, beginning with “A method comprising…,” and is distinct from a “product-by-process (PBP) claim,” which describes a manufacturing process within a product claim.In Japan, regarding PBP claims, the Supreme Court’s June 5, Heisei 27 ruling (the Pravastatin Sodium case) held that the scope of protection is determined by the product itself, not the manufacturing process (the “product-identity theory”),and that the requirement for clarity is satisfied only in cases where it is “impossible or impractical” to define the subject matter based on its structure or characteristics. Therefore, the indiscriminate use of PBP claims is not recommended.
Furthermore, the numerical limitations in Claim 1 (plate thickness of 0.020 to 0.160 inches, within 1 inch from the face) clarify the outer boundaries of the scope of protection, but also create room for circumvention through design changes outside that scope.In Japanese examination practice, the inventive step of an invention with numerical limitations is assessed based on the advantageous effects or critical significance within the limited scope; however, the 8-fold range in this case can be viewed as a “range-securing” type of numerical limitation that broadly encompasses a feasible design space rather than representing a critical value (this assessment is the author’s own analysis).From the perspective of competitors, such numerical and positional limitations become potential design workarounds to consider during FTO analysis.
The Rules of Equipment are essential for understanding the competition in golf club development. The R&A’s Rules of Equipment set the following upper limits for wood-type clubheads (verified on the R&A’s official website).
| Regulatory Parameters | Upper Limit |
|---|---|
| Head Volume | 460 cc (±10 cc) |
| Moment of Inertia (MOI, about the vertical axis) | 5,900 g·cm² (+ test tolerance of 100) |
| Face Rebound (CT Value: Pendulum Test) | 239 microseconds (+ test tolerance of 18 μs) |
| Dimensions | Heel-to-toe: 5 inches or less; Sole-to-crown: 2.8 inches or less |
Since there are upper limits on volume, rebound, and moment of inertia, the competition in development is shifting toward “how to differentiate within those limits.”Where to reallocate the discretionary mass freed up by thinning the face and body; whether to standardize rebound close to the upper limit across the entire face—including areas beyond the regulation’s measurement points; and how to minimize variation during mass production to prevent products from exceeding tolerances—Patents such as this one, involving “stress-reduction structures combined with precision casting processes,” fit squarely into this context (the regulatory values have been verified using primary sources; the analysis in this paragraph reflects general industry understanding).Interestingly, the patent classification (CPC) also lists subcategories under A63B53/04 (head) such as volume (53/0412), dimensions (53/0408),grooves (53/0445), and reinforcing ribs (53/045)—subclassifications that appear to correspond to the regulatory items in the rules.
Competition for differentiation under this “ceiling” is sometimes taken to court. Here are some representative examples.
| Case | Overview and Outcome |
|---|---|
| Callaway v. Acushnet (Lawsuit filed in 2006) | The Titleist Pro V1 ball was at issue.In 2007, a jury returned a verdict largely in Callaway’s favor → In 2009, the CAFC vacated and remanded the case on the grounds of inconsistent jury verdicts → In the 2010 retrial, the court ruled the patent at issue invalid → In April 2012, a comprehensive settlement was reached without any monetary exchange.A case where the tables turned in six years |
| PXG v. TaylorMade (Lawsuit filed in 2017) | PXG filed a lawsuit three days before the release of the P790 irons and sought a preliminary injunction → The injunction was denied, and the product was released → TaylorMade filed a counterclaim (based on media reports) → The case was settled in February 2019 through a cross-licensing agreement |
| Bridgestone v. Acushnet (2005–) | An example where a Japanese company took the offensive. In the U.S., the case was settled in October 2007 through the payment of license fees and a cross-licensing agreement.In Japan, a February 26, 2010, ruling by the Tokyo District Court (plaintiff: Bridgestone Sports) found infringement of a golf ball patent and ordered Acushnet Japan to pay approximately 1.78 billion yen (the outcome of the appeal has not been confirmed for this article). |
| TaylorMade v. Costco et al. (Filed in 2024; pending) | TaylorMade alleges that the Kirkland Signature irons infringe five P790-related patents (along with claims of false advertising). Proceedings are reportedly suspended due to an interlocutory appeal, and as of July 2026, no reports of a final ruling have been confirmed. |
Note: The TaylorMade v. Costco lawsuit is pending, and the information above is based solely on the plaintiff’s allegations. It does not prejudge the merits of the infringement claims or the validity of the patents. For guidance on interpreting pending litigation, please also refer to the explanatory article on the Kioxia v. Viasat patent lawsuit.
The Callaway v. Acushnet case is a textbook example of the principle that “a jury verdict is not a final judgment,” as the jury verdict (2007, in favor of the plaintiff) was overturned on appeal and remanded, ultimately resulting in the invalidation of all patents (2010).Furthermore, it is a characteristic of this industry that the same product—the P790—appears in both the defending and attacking roles at different times, as seen in the PXG v. TaylorMade and TaylorMade v. Costco cases.It should be noted, however, that the famous dispute surrounding the “square grooves” of the PING Eye 2 around 1990 was a lawsuit concerning compliance with equipment rules rather than a patent dispute; it is important to distinguish this difference in nature.
Japanese club manufacturers are also continuously securing patents in their respective areas of expertise. The following are examples of registered patents for which our firm verified the bibliographic details directly on Google Patents (as of July 18, 2026; these represent only a small fraction of each company’s patent portfolio).
| Patent Number | Patentee | Key Technical Features |
|---|---|---|
| Patent No. 6809352 | Sumitomo Rubber Industries | Reduces vibration and enhances rebound performance using the raised and sloped surfaces of the crown section and the inner wall ribs |
| Patent No. 7760356 | Bridgestone Sports | Achieves both a satisfying feel at impact and high moment of inertia through the design of the recess in the cavity back of the iron |
| Patent No. 6770600 | Mizuno | Fine, sloped grooves between the score lines promote drainage in rainy conditions and maintain wet spin |
| Patent No. 6796496 | Yonex | Method for manufacturing a hollow head using carbon prepreg and metal (expansion of a bag-shaped elastic body and vacuum extraction). Examples of manufacturing method claims by Japanese companies |
| Patent No. 7181852 | Globride (ONOFF) | The thin-walled section on the back of the face is positioned outside the effective impact area (10 mm radius), achieving both rebound and durability |
| Patent No. 7004927 | Pro Gear | By limiting the range of side weight placement, both moment of inertia and a center of gravity on the clubface are achieved |
Sumitomo Rubber’s crown vibration suppression and Glovebride’s thin-wall placement are part of the same lineage of thinking as the Callaway patent discussed in this article—namely, “stress and stiffness design within the limits of maximum rebound.”Furthermore, Yonex’s manufacturing method patent is a claim unique to the company, which excels in materials (carbon molding); the choice of which layer to secure rights for reflects each company’s business structure, making it a useful point of comparison with U.S. firms.
① US11,083,937 is a process patent that defines the unit of invention as the manufacturing process involving assembly in a wax mold followed by integral casting, and it delineates the scope of the invention through numerical and positional limitations.② It is part of a family strategy that alternately secures “articles” and “methods” within a chain of multi-stage CIP and divisional applications dating back to a provisional application filed in 2012.③ The enforceability of process claims differs between the U.S. under Section 271(g) and Japanese evidentiary practices, reflecting the need to tailor claim structures to each country—these three points form the backbone of this article.
Checkpoints for Patent Practice in Product Fields with Performance Limits (Equipment Regulations, Safety Standards, Industry Standards)
Please also see our related articles: an article on division application strategies explaining the practical aspects of forming patent families; an article on the Kioxia v. Viasat litigation explaining how to interpret pending litigation; and an article on Materials Informatics × AI patents as an example of patent trend analysis in the technical field.
Companies considering patent applications in the sporting goods and consumer goods sectors (including the appropriate use of claim categories and international filing strategies), as well as the analysis of competitor patent families and FTO investigations, are welcome to contact us via the inquiry form on the EVORIX Intellectual Property Office website.
[Disclaimer] This article is a general explanation based on publicly available information as of July 18, 2026 (including Google Patents, J-PlatPat, WIPO PATENTSCOPE, the R&A official website, court records, and media reports), and does not constitute legal advice.While the bibliographic details of the patents mentioned in this article have been verified on the actual pages of public databases, this does not constitute an interpretation of the scope of protection or an assessment of validity, nor does it indicate any business relationship between the companies mentioned and our firm. The TaylorMade v. Costco litigation is pending, and the description includes information based on the plaintiff’s allegations at this stage.The outcome of the appeal regarding the Tokyo District Court’s ruling in Bridgestone v. Acushnet has not yet been determined. The numerical values in the Rules of Golf are based on materials published by the R&A; please refer to the original source for the most up-to-date rules. Citations of case law are summaries based on published analyses of court decisions. (Supervised by a patent attorney)