Bolted Connections Patents: Who Leads, Where the Gaps Are 2026
- 78.8% of all 113 records in scope sit with just five assignees, making this one of the more concentrated corners of steel-structure patenting.
- Filing peaked in 2017 at 7 and the trend line has not been repeated since, though the most recent years are understated by publication lag.
- Metallurgy dominates the claim language C22C alloy compositions and C21D heat treatment together outweigh F16B fastener-structure claims, meaning most of the fight is over the steel, not the joint.
Top-5 share is the combined record count of the five largest assignees divided by all 113 records in scope (CR5), not by the ranked leaders only.
What this patent set covers
This landscape tracks patents at the intersection of slip-critical joint design and high-strength bolting — the hardware and metallurgy that keep steel connections from slipping under load. The search combines faying-surface treatment and slip-coefficient language with bolt-specific failure modes: pretension loss, turn-of-nut installation, bolt relaxation, hydrogen embrittlement and direct tension indicators. That pairing pulls in both structural-engineering filings and steel-metallurgy filings, which is why the technology composition leans so heavily toward alloy and heat-treatment classes rather than fastener geometry alone.
113 published records sit in scope, spanning receiving offices in Japan, the United States, Europe, Canada, China and Germany. Japan alone accounts for the largest share of filings, consistent with a corpus where steelmakers rather than construction-hardware firms hold most of the deep claim positions.
Filing trend and technology composition
Two views of the same 113 records: how filing activity has moved year over year, and which IPC subclasses carry the claim language. Because a single record can carry several IPC codes, the technology shares add up to more than 100% of the record total.
Filing trend, 2017–2026
Filing rose to a peak of 7 records in 2017 and has not returned to that level since. With fewer than four complete years remaining once publication lag is factored in, a growth rate cannot be reliably computed from this window — treat the most recent years as undercounted rather than as a genuine decline.
Technology composition by IPC subclass
C22C (alloys) appears in 63.7% of the 113 records and C21D (heat treatment of metals) in 43.4%, together dwarfing F16B (fasteners) at 33.6%. Smaller pockets sit in C23C coatings, E04B building structures, B21B rolling, H01M batteries and B32B laminates, each in single-digit percentages of the record total — these are the branches worth checking individually rather than assuming they are covered by the metallurgy majors.
Shares are the percentage of the 113 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Bolted Connections and Slip Critical Joints with Eureka
This page is one run against one query. Ask Eureka your own question about bolted connections and slip critical joints and every answer comes back with the patent numbers behind it.
Try EurekaThe most-cited records in this set
High strength bolt having excellent hydrogen embrittlement resistance
The filing specifies a high-strength bolt steel composition — controlled carbon, silicon, manganese and aluminium ranges — combined with a microstructure built around residual austenite, bainitic ferrite and martensite, engineered specifically to resist hydrogen embrittlement while retaining bolt strength.Filed by Kobe Steel; representative of the metallurgy-first approach that dominates this corpus.
View full filing| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US3992974A | Conical washer for a high tensile strength bolt | 58 |
| 2 | US20140234658A1 | Galvanized steel sheet and method of manufacturing the same | 55 |
| 3 | CN1900344A | 耐延迟断裂特性优良的高强度螺栓及其制造方法 | 47 |
| 4 | JP2004307929A | Bolt having excellent hydrogen embrittlement resistance, and its production method | 38 |
| 5 | JP2007031734A | High strength bolt having excellent delayed fracture resistance, and method for producing the same | 31 |
| 6 | JP1987086149A | Tough and hard bolt steel | 28 |
| 7 | US20160370268A1 | Failure detection sensor, failure detection system, and structure | 20 |
| 8 | EP2762590A1 | Galvanized steel sheet and method of manufacturing same | 20 |
| 9 | JP1989052045A | High-strength bolt | 20 |
| 10 | JP1983084960A | High tensile steel with superior delayed rupture resistance | 17 |
Citation counts inside a searched corpus favour older filings — read them as a signal of influence on later work, not as a measure of current commercial importance.
Patent titles are shown in the language they were filed in, not translated, so that each record stays verifiable against the original filing — a translated title will not match in Eureka or in any national register. Each row carries its publication number; clicking a row searches Eureka by that number.
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Three patterns stand out once the records are broken down by assignee, class and geography.
Five assignees hold most of the field
The leader alone accounts for 50 records, and the top five combined cover 78.8% of all 113 records in scope. That is a steep concentration curve for a niche this specific — new entrants are not filing into open ground, they are filing around a small number of dominant steelmakers.
Alloy chemistry, not joint geometry, is the battleground
C22C alloy claims and C21D heat-treatment claims each outrank F16B fastener-structure claims. Anyone entering this space through mechanical joint design alone is filing alongside claims that are really about steel composition and processing.
No assignee shows recent-year filing activity
Every leading assignee tracked for recent-year momentum shows zero filings in the latest year on record. Combined with publication lag of roughly 18 months, this reads more as a reporting gap than a real stop in R&D, but it means the newest strategic moves are not yet visible in the public record.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to bolted connections and slip critical joints, with the prior art for and against each one.
| Assignee | Co-assignee | Shared families |
|---|---|---|
| Nippon Steel Corporation | Honda Motor Co., Ltd. | 10 |
| Kobe Steel, Ltd. | Shinshu TLO Co., Ltd. | 7 |
| WATANABE ATSUSHI | TOMIMOTO ATSUSHI | 4 |
| Nippon Steel Corporation | NITTETABU BORUTEN | 2 |
| Daido Steel Co., Ltd. | Nissan Motor Co., Ltd. | 2 |
| Daido Steel Co., Ltd. | Minohashi Co., Ltd. | 2 |
| Nippon Steel Corporation | Nippon Steel & Sumikin Engineering Co., Ltd. | 1 |
| Nippon Steel Corporation | WATANABE ATSUSHI | 1 |
Ten co-assignee pairs appear in the dataset. The strongest pairing recurs 10 times, pointing to a steady joint-development relationship between a steelmaker and an automotive OEM rather than a one-off collaboration.
Who holds the claim positions
The ranking covers 28 companies — the complete set the data endpoint returns for this search, not a top-50 or top-100 cut. Filing is heavily front-loaded: the leader holds 50 records, fifth place holds 6, and by tenth place the count has fallen to 3.
One steelmaker anchors the field
The leading assignee's record count is close to the combined total of the next four ranked companies, indicating a long-running, well-resourced filing programme rather than opportunistic patenting.
A steep drop after the top ten
By the tenth-ranked assignee, filing counts have dropped to 3 records, and the top ten together already cover 97.3% of all records in scope — leaving very little volume for the remaining eighteen ranked companies.
Joint filings cluster around a few relationships
The strongest co-assignee pairing recurs 10 times, linking a steelmaker with an automotive manufacturer — a pattern consistent with bolt steel developed for automotive structural applications rather than construction alone.
| Assignee | Recent year | YoY |
|---|---|---|
| Nippon Steel Corporation | 0 | — |
| NIPPON STEEL & SUMITOMO METAL CORP | 0 | — |
| Kobe Steel, Ltd. | 0 | — |
| Honda Motor Co., Ltd. | 0 | — |
| Shinshu TLO Co., Ltd. | 0 | — |
| Toyo Kohan Co., Ltd. | 0 | — |
| Daido Steel Co., Ltd. | 0 | — |
| Hiei Kensetsu Co., Ltd. | 0 | — |
Where to take this analysis
The patterns above point to specific follow-up work depending on whether the goal is freedom-to-operate, competitive tracking or white-space filing.
Check freedom-to-operate against the top five
With 78.8% of records held by five assignees, any new bolt-steel or slip-critical joint filing should be checked directly against their claim scope before drafting.
Explore assignee claims in EurekaTrack the metallurgy-fastener boundary
Because C22C and C21D claims outnumber F16B claims, a filing strategy focused only on mechanical fastener geometry may be missing the composition claims that actually control the space.
Map IPC overlap in EurekaWatch for the publication-lag catch-up
Zero recent-year momentum across leading assignees is likely a reporting artefact of publication lag rather than a real pause — recheck this trend in six to twelve months.
Set a filing alert in EurekaCommon questions on this landscape
Filing in this space is concentrated: the top five assignees account for 78.8% of all 113 records in scope, and the single leading assignee holds 50 records on its own. The ranking includes 28 companies in total, but by the tenth-ranked firm the count has already fallen to 3 records. Most of the leading holders are Japanese steelmakers, which lines up with Japan being the largest receiving office in this dataset, followed by the United States and Europe.
A slip-critical joint relies on friction between clamped steel surfaces, generated by high bolt pretension, to transfer load without the bolt shank ever bearing directly. Hydrogen embrittlement is a delayed-fracture risk in the high-strength bolt steel itself, where absorbed hydrogen can cause sudden failure under sustained clamping load. That is why a large share of the patent activity here — including the most-cited records in this dataset — targets bolt steel microstructure specifically to resist embrittlement rather than only optimising joint geometry.
Filing peaked in 2017 at 7 records and has not returned to that level in the years since, based on the trend data in scope. However, publication typically lags filing by around 18 months, so the most recent one to two years understate real filing activity and should not be read as a genuine slowdown. Recent-year momentum figures showing zero filings from leading assignees are best treated as an incomplete record rather than a stop in R&D.
The technology composition skews heavily toward alloy chemistry (C22C, 63.7% of the 113 records) and heat treatment (C21D, 43.4%), with fastener structure (F16B) and building-structure integration (E04B) each carrying a smaller share. That gap suggests under-claimed ground in areas like faying-surface coating durability, direct tension indicator calibration, and sensor-based bolt relaxation monitoring — branches adjacent to the metallurgy core but not yet as densely filed.
With the top five assignees holding 78.8% of all 113 records and the top ten holding 97.3%, this field is more concentrated than a typical long-tail technology area. Only 28 companies appear in the ranking at all, and the drop-off after the top ten is steep, down to single-digit record counts. That combination — high concentration at the top, thin ranks below it — means a new entrant is more likely to succeed by targeting a specific under-claimed sub-area than by competing broadly against the leaders.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.