Other Engine Equipment Manufacturing (U.S.) — Investor Primer

NAICS 2022 code 333618 — Other Engine Equipment Manufacturing. (NAICS = North American Industry Classification System, the standard code the U.S. government uses to group businesses.)

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1. Overview

This is the industry that builds the internal-combustion engines that move and power almost everything except passenger cars and aircraft: the diesel engines in trucks, bulldozers, tractors, tugboats, and locomotives; the gas and diesel gensets (generator sets) behind hospitals, factories, and data centers; the small gasoline engines under lawn mowers and pressure washers; and the big marine engines in Navy ships. If it burns fuel to make mechanical power and it isn't a car or a plane, it likely came from an establishment classified here.

Why an investor should care: engines are a cyclical, capital-goods business tied to the freight, construction, farm, marine, and power cycles — but with an unusually durable, high-margin aftermarket (parts, service, rebuilds) layered on top, because an engine sold today throws off parts-and-service revenue for 15 to 30 years. Right now the industry sits at an interesting crossroads: a once-in-a-generation surge in electricity demand from data centers is pulling hard on generator engines [7][8], while long-run decarbonization pressure hangs over combustion itself.

Public vs. private ways in. There is essentially one large-cap that is close to a pure play — Cummins (ticker CMI) [4][5]. Beyond that, engine-making is buried inside diversified equipment giants (Caterpillar, Deere, Wabtec) or held by private-equity firms (Briggs & Stratton, Rehlko/Kohler, Fairbanks Morse) [14][15][16]. There is no dedicated engine ETF (exchange-traded fund).

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2. What it is & how it's structured

Scope (what counts as 333618). Establishments primarily engaged in manufacturing internal-combustion engines except automotive gasoline and aircraft engines [1]. The key word "other" means the residual engine category after automotive gasoline and aircraft are carved out — not miscellaneous engine equipment. Highway-truck diesel engines belong here even though highway gasoline engines do not [17]. The scope includes:

• Diesel and semi-diesel engines (the core of the industry)
• Natural-gas engines
• Gasoline engines other than automotive and aircraft (e.g., small engines for lawn/garden and portable equipment)
• Marine engines and outboard motors (Census also anomalously assigns electric outboard motors to this code) [17]
• Diesel locomotive engines
• Engine governors and related parts [1]

What it EXCLUDES — this matters, because "engines" get scattered across several codes:

• Automotive gasoline engines and parts → NAICS 336310 (Motor Vehicle Gasoline Engine and Engine Parts Mfg.) [1]
• Aircraft engines → NAICS 336412 (Aircraft Engine and Engine Parts Mfg.) [1]
• Turbines and turbine-generator sets (jet-derivative, gas, steam, hydro) → NAICS 333611 [1]
• Power-transmission gear, speed changers → NAICS 333612 / 333613 [1]
• The lawn mower, tractor, or ship the engine goes into is classified with the finished machine, not here.

Operating model. Manufacturers typically design the combustion system and block architecture; engineer an engine for a customer's vehicle, vessel, or machine; source castings, forgings, fuel systems, electronics, and aftertreatment; machine and assemble the engine; calibrate software; validate it in test cells; certify each engine family; and support it through dealers and distributors [5][18][19]. Engines are rarely drop-in commodities: cooling, controls, emissions calibration, packaging, and duty-cycle validation must be integrated with the host equipment, which raises switching costs but also makes the supplier dependent on winning and retaining OEM platforms.

Ownership mix. Five flavors: (1) one large merchant/public multinational (Cummins) [4]; (2) captive engine divisions inside diversified public equipment makers (Caterpillar's engine and Progress Rail/EMD units, Deere Power Systems, Wabtec's rail engines) [3][6]; (3) a focused public marine-propulsion producer (Brunswick's Mercury Marine) [19]; (4) foreign-owned operations on U.S. soil (Detroit Diesel, owned by Germany's Daimler Truck); and (5) private-equity-owned platforms (Briggs & Stratton under KPS Capital Partners; Rehlko, formerly Kohler Energy, majority-owned by Platinum Equity; Fairbanks Morse Defense under Arcline) [14][15][16]. Around the edges sit many small private engine shops and remanufacturers.

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3. How big it is

Federal figures for U.S. NAICS 333618:

Concentration. This is a top-heavy but not monopolized industry. The four largest firms make 62.7% of shipments, the top eight 76.2%, the top twenty 88.3%, and the top fifty 95.9% [2]. The Herfindahl-Hirschman Index (HHI, a standard concentration score) is 1,303 [2] — just below the 1,500 line the U.S. antitrust agencies treat as "moderately concentrated," i.e., dominated by a handful of large players with a long tail of small ones. The U.S. Small Business Administration size standard here is 1,500 employees, meaning a firm can be quite large and still count as "small" for federal contracting [as ingested; SBA 2023].

The undercount caveat — read this before you size the market. Unlike restaurants or trades, this industry is not undercounted by tiny or individual operators; it's capital-intensive factory work. The distortion runs the other way: the code draws a narrow boundary, so the $28 billion figure understates the economic footprint of "engines" broadly. Engine value that is vertically integrated into a finished vehicle or machine gets counted with that machine, not here; automotive gasoline engines (336310), aircraft engines (336412), and turbines (333611) each live in their own codes; and a large share of engines sold in the U.S. is imported and never shows up in domestic shipments at all. Company segment revenue cannot simply be added to obtain the NAICS market: Cummins Engine includes international and automotive-related activity; Caterpillar Power & Energy includes turbines, rail, and services; Brunswick Propulsion includes propellers, controls, and rigging. So treat $28 billion as the value of engines shipped from U.S. plants whose main job is making engines — a real but partial slice of the country's engine economy. For scale: Cummins alone reported $34 billion in total 2024 revenue [4], more than the entire domestic-shipments figure, because much of that is distribution, components, and overseas sales that fall outside this one code.

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4. The investable universe

Public companies (direct or heavy exposure). Reserve the tickers and market caps below for this section only.

Foreign-listed relevance: Rolls-Royce (Power Systems/MTU diesel & gas engines), Daimler Truck (Detroit Diesel), Volvo Group, Traton, Deutz, Kubota, Mitsubishi Heavy Industries, and Weichai Power (China).

Major private / other owners.

• Detroit Diesel — subsidiary of Daimler Truck AG (heavy-duty on-highway diesels)
• Rehlko (formerly Kohler Energy: Kohler Engines + Power Systems) — majority-owned by Platinum Equity since May 2024 [14]
• Briggs & Stratton — owned by KPS Capital Partners, acquired out of Chapter 11 in 2020 for ~$550 million (small gasoline engines) [15]
• Fairbanks Morse Defense — owned by Arcline Investment Management (naval/marine diesel engines, incl. U.S. Navy submarines) [16]
• Many small private engine builders and remanufacturers

Bottom line for stock pickers: if you want listed exposure concentrated in this industry, it's Cummins first, then Generac and Wabtec, then Brunswick for marine, then diffuse exposure through Caterpillar/Deere/PACCAR. Everything else of scale is in private-equity or foreign hands.

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5. How the money works

Engine makers earn money on two very different clocks.

New-engine sales — cyclical and mid-margin. The lever is unit volume × price − input cost. Because factories, tooling, and R&D are large fixed costs, this is a high-operating-leverage business: when volumes rise, incremental units drop a lot to the bottom line; when volumes fall, margins compress fast. Capacity utilization is therefore the single most-watched operational number. Based on dated EPA industry data (2002 Economic Census), materials represented roughly 64% of shipment value, labor 12%, and capital expenditures 4%, with iron/steel at 12% of material cost and aluminum 6% [20]. While current shares differ, the sensitivity to castings, forgings, steel, aluminum, electronics, tariffs, and freight persists. Pricing power depends on position: a captive engine (Caterpillar or Deere building engines for their own machines) is priced inside the finished product, while a merchant supplier like Cummins negotiates with truck and equipment OEMs (original equipment manufacturers) such as PACCAR and Stellantis.

Operating leverage in action. Cummins illustrates the margin swing: its Engine segment generated $10.9 billion of sales and $1.4 billion of EBITDA in 2025, a 12.7% margin, down from $11.7 billion and $1.7 billion (14.1% margin) in 2024 — lower truck volumes, unfavorable mix, product-coverage costs, and material costs outweighing pricing [5]. Marine propulsion shows similar cyclicality: Brunswick Propulsion recorded an 8.9% operating margin in 2025, down from 11.7% in 2024, with tariffs and compensation costs outweighing pricing and absorption benefits [19].

Aftermarket — the annuity. Here is the real profit engine. An engine runs for 15-30 years and needs filters, injectors, gaskets, overhauls, and rebuilds the whole time — sold at higher margins than the original engine and far less cyclically. This is a classic razor/razorblade model: sell the engine to build an installed base, then harvest parts and service for decades. Cummins' Distribution segment alone generated $11.4 billion of 2024 sales — larger than its new-engine segment [4] — which is why investors prize a big installed base and a dense dealer/service network. Brunswick's Engine Parts and Accessories segment earned an 18.1% operating margin in 2025, supporting the general observation that installed-base parts can be materially more profitable than new engines [19].

Backlog and certification as moats. Large engines (marine, locomotive, prime-power gensets) sell against multi-quarter order backlogs, giving some revenue visibility. And meeting ever-tighter emissions rules requires expensive aftertreatment engineering and government certification — a barrier that protects incumbents from new entrants. Competitive variables include performance, price, total cost of ownership, fuel economy, emissions compliance, delivery, quality, and service — not simply engine purchase price [5]. Watch: unit build rates, capacity utilization, aftermarket/parts mix, backlog, incremental (drop-through) margins, and R&D intensity.

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6. What drives demand

Demand is the sum of several independent cycles, which is both a risk and a diversifier:

• Heavy trucking / freight — Class 8 (the heaviest highway trucks) build rates drive on-highway diesel demand. A U.S. freight recession through 2024-2025 has been a sharp headwind: Cummins reported 2025 North American heavy-duty engine shipments fell 27% and medium-duty truck-and-bus shipments fell 31% [5][10].
• Construction & agriculture — off-highway diesel for excavators, loaders, and tractors; rate- and commodity-sensitive. AEM (Association of Equipment Manufacturers) reported U.S. low-horsepower tractor shipments running 13% below the prior year in December 2024, while describing high-horsepower agriculture as near a deep cycle low entering 2026 [21][22].
• Power generation — the standout current driver. Backup and prime-power gensets for data centers are surging on cloud and artificial-intelligence (AI) demand: diesel generator capacity at U.S. data centers nearly tripled from ~20 gigawatts in 2018 to ~55 gigawatts in 2024 [9], and the data-center generator market is projected to roughly double from ~$9.5 billion (2025) toward ~$19.7 billion by 2034 [8]. Caterpillar's 2025 power-generation sales increased 32%, led by large reciprocating engines for data centers [18]. Where the grid can't deliver power for years, developers increasingly install natural-gas engines for prime power, not just backup [8][9].
• Marine — commercial vessels, recreational boating, plus Navy/Coast Guard programs (Buy-American, Jones Act) that favor domestic builders like Fairbanks Morse [16]. Marine is discretionary and interest-rate sensitive: U.S. outboard-engine sales fell 7.6% to 278,000 units in 2024, but retail value reached $3.6 billion as high-horsepower demand held up — engines rated at 300 HP and above sold more than 40,000 units and generated $1.2 billion, nearly 35% of category value [23]. This is a good example of mix supporting dollars and margins while units decline.
• Rail — freight-locomotive replacement and rebuilds (Wabtec, Progress Rail/EMD) [7].
• Oil & gas — drilling, fracking pumps, and gas compression.
• Replacement / aftermarket — the steady base that cushions new-equipment downturns.

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7. Regulation

Emissions rules are the industry's defining regulatory force — simultaneously a cost, a barrier to entry, and a product-cycle driver. EPA maintains distinct rules and test procedures for nonroad diesel, stationary diesel, small and large spark-ignition, marine diesel, marine gasoline, and heavy-duty highway engines [24]. Every heavy-duty and nonroad engine class introduced into U.S. commerce requires a certificate of conformity valid for one production model year [25].

• EPA off-road standards. "Tier 4," phased in 2008-2015, cut nonroad diesel NOx (nitrogen oxides) and PM (particulate matter) by roughly 90% versus prior tiers, forcing SCR (selective catalytic reduction) and DPF (diesel particulate filter) aftertreatment and ULSD (ultra-low-sulfur diesel, ≤15 ppm sulfur) fuel [11]. Meeting these standards is expensive but keeps low-tech competitors out.
• The 2027 heavy-duty NOx rule. A tighter on-highway standard (0.035 g/hp-hr NOx) takes effect model-year 2027. As of late 2025 the EPA has kept the 2027 timeline and core limit despite a trucking-industry request to delay it four years, while signaling it may soften related warranty/useful-life provisions [10]. EPA's heavy-duty Phase 3 rule page notes subsequent reconsideration and policy changes, creating planning risk because product programs and factories must be committed years before the applicable model year [26]. Tightening rules often trigger a pre-buy — fleets order engines before the rule to avoid pricier post-rule versions — pulling demand forward and then leaving an air-pocket after.
• California small off-road engines (SORE). California's rule requires most newly manufactured small off-road engines to be zero-emission from model year 2024 and targets portable generators for zero-emission standards beginning in 2028 [27]. This directly affects small-engine makers like Briggs & Stratton in the state's market.
• GHG / fuel-economy (EPA Phase 2/3) for heavy trucks, plus California's CARB (California Air Resources Board) standards, add a second regulatory track and periodic uncertainty as rules are proposed, litigated, and reconsidered.
• Enforcement risk is real. Manufacturers carry in-use warranty, defect-reporting, and recall exposure; EPA can require recalls when a substantial number of properly maintained engines fail in-use standards. In 2023-2024 Cummins agreed to a record ~$2 billion Clean Air Act settlement (a $1.675 billion civil penalty plus ~$325 million in remediation and a recall of 600,000+ Ram trucks) over "defeat device" software — the largest such penalty ever [12][13]. It's a reminder that certification cheating carries franchise-level consequences.
• Decarbonization is the long shadow: policy is nudging the industry toward natural gas, hydrogen combustion, and eventual electrification. Batteries and electric motors are most credible in lawn and garden equipment, compact machinery, some commercial vehicles, and marine applications. Large, remote, continuous-duty, marine, and heavy-load applications are harder to electrify because of energy density, charging, and uptime requirements — hybrid systems, renewable diesel, natural gas, methanol, hydrogen combustion, and improved controls are therefore likely to coexist with battery products [27].

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8. Competitive dynamics & consolidation

The structure is a handful of scaled incumbents (top four = 63% of shipments [2]) plus a long tail, and it has been consolidating:

• Wabtec was formed by merging Westinghouse Air Brake with GE Transportation (2019), concentrating North American locomotive and rail-engine manufacturing [7].
• Cummins acquired Meritor (drivetrain) in 2022, deepening its powertrain footprint [4].
• Private equity is actively rolling up the private side: Platinum Equity carved out Kohler Energy and rebranded it Rehlko (2024) [14]; KPS rebuilt Briggs & Stratton post-bankruptcy (2020) [15]; and Arcline is assembling a naval-engine platform around Fairbanks Morse [16].
• Vertical integration vs. merchant supply is the key strategic split: captive makers (Caterpillar, Deere) protect margin by supplying their own machines, while merchant suppliers (Cummins, PACCAR's MX) compete for OEM sockets. Barriers to entry — emissions certification, capital intensity, brand/reliability reputation, and service-network density — are high, which is why the incumbent set changes slowly. International competition (China's Weichai, European groups) bites mainly in export markets.

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9. Risks

• Cyclicality. Revenue swings with the freight, construction, and farm cycles; the 2024-2025 freight recession is a live example with Cummins' heavy-duty shipments down 27% [5][10]. High operating leverage magnifies both up- and down-cycles.
• Energy transition (secular). The core product is combustion. Long-run electrification of trucks, off-road equipment, and backup power is an existential question mark; natural-gas and hydrogen engines and fuel-agnostic platforms may extend the runway, but the terminal-value debate is unresolved. (forward-looking)
• Regulatory whipsaw. Emissions rules tighten, get litigated, and get reconsidered — raising R&D cost and muddying product planning, and creating pre-buy/air-pocket demand distortions [10][26].
• Enforcement / litigation. Certification missteps are franchise-threatening — see the ~$2 billion Cummins settlement [12][13]. Manufacturers also carry in-use warranty, defect-reporting, and recall exposure.
• Input costs & supply chain. Steel, castings, semiconductor availability, and tariffs drive margins and delivery. Brunswick cited tariffs as a key 2025 margin drag [19].
• Customer concentration. A few large truck and equipment OEMs and data-center buyers wield pricing leverage.
• Data-center demand risk. The genset boom is a powerful tailwind but could prove cyclical or lumpy if AI/data-center buildout slows [8][9]. (forward-looking)
• Trade / tariffs. Import competition and tariff policy cut both ways for domestic producers.
• OEM insourcing. Equipment makers may bring engine production in-house, displacing merchant suppliers.

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10. How to invest & the outlook

Public-market routes. The cleanest listed exposure is Cummins (CMI) — engines plus power systems plus a large aftermarket annuity, though its Components, Distribution, Power Systems, and zero-emission Accelera businesses materially affect consolidated results [4][5][6]. For power generation specifically, Generac (GNRC) rides the backup/prime-power theme, and Wabtec (WAB) captures rail engines [6][7]. Brunswick (BC) offers more focused marine-engine and aftermarket exposure through Mercury Marine [19]. For diversified, indirect exposure, Caterpillar (CAT), Deere (DE), and PACCAR (PCAR) each embed sizable captive engine operations [18]. There is no pure-play engine ETF; broad industrials or capital-goods funds only dilute the theme. Public investors are effectively buying a cyclical with an aftermarket cushion — so the aftermarket/parts mix, incremental margins, and order backlog matter as much as headline sales.

Private-market routes. Much of the industry's scale sits in private hands: Briggs & Stratton (KPS) [15], Rehlko (Platinum Equity) [14], and Fairbanks Morse Defense (Arcline) [16] are private-equity platforms; access comes through PE funds or eventual exits/IPOs. The aftermarket itself — independent dealers, remanufacturers, and service shops — is highly fragmented and a natural roll-up target for smaller private buyers. Underwriting should separate recurring parts and service from cyclical new-engine sales, quantify customer and platform concentration, test tariff pass-through, and reserve conservatively for emissions, warranty, and legacy liabilities.

Near-term drivers (forward-looking). The clearest tailwind is electricity demand: data-center backup and prime-power gensets, in both diesel and natural gas, are the standout growth vector into the late 2020s — Caterpillar's power-generation sales rose 32% in 2025, led by large reciprocating engines for data centers [8][9][18]. This is reinforced by reshoring capex and defense/naval programs. Offsetting that are a soft heavy-truck cycle [5][10] and the 2027 EPA pre-buy/air-pocket dynamic that can whipsaw truck-engine volumes [10]. Long term, the swing factor is the energy transition: how far natural gas, hydrogen combustion, and fuel-agnostic engine platforms can extend the internal-combustion franchise before electrification erodes it. For now the installed base, the aftermarket annuity, and the power-generation surge keep this a cash-generative, if cyclical, corner of industrial manufacturing.

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Sources

1. NAICS Association. "NAICS Code 333618 — Other Engine Equipment Manufacturing (description)." 2022. https://www.naics.com/naics-code-description/?code=333618
2. U.S. Census Bureau. "2022 Economic Census — Concentration & receipts, NAICS 333618." 2022. (Ingested ground-truth: receipts $28.07B; CR4 62.7%, CR8 76.2%, CR20 88.3%, CR50 95.9%; firms 246; HHI 1,303.) https://www.census.gov/programs-surveys/economic-census.html
3. U.S. Census Bureau. "County Business Patterns, NAICS 333618." 2023. (Ingested ground-truth: employment 42,686; establishments 263; annual payroll $3.16B.) https://www.census.gov/programs-surveys/cbp.html
4. Cummins Inc. "Form 10-K, FY2024 (segment revenue: Engine $8,987M, Components $9,894M, Distribution $11,352M, Power Systems $3,500M, Accelera $369M; total net sales ~$34.1B)." U.S. SEC, 2025. https://www.sec.gov/Archives/edgar/data/26172/000002617225000007/cmi-20241231.htm
5. Cummins Inc. "Form 10-K, FY2025 (Engine segment $10.9B sales, $1.4B EBITDA at 12.7% margin; HD engine shipments −27%, MD −31%)." U.S. SEC, 2026. https://www.sec.gov/Archives/edgar/data/26172/000002617226000009/cmi-20251231.htm
6. CompaniesMarketCap. "Cummins (CMI), Generac (GNRC), Wabtec (WAB) — market capitalization & revenue." 2026. https://companiesmarketcap.com/cummins/marketcap/
7. Wikipedia. "Wabtec." 2025. https://en.wikipedia.org/wiki/Wabtec
8. Fortune Business Insights. "Data Center Generator Market Size, Share & Forecast 2026-2034." 2026. https://www.fortunebusinessinsights.com/data-center-generator-market-114458
9. Latitude Media. "The data center boom is a diesel generator boom." 2025. https://www.latitudemedia.com/news/the-data-center-boom-is-a-diesel-generator-boom/
10. Commercial Carrier Journal. "EPA Rejects Trucking Industry Plea, Will Keep 2027 NOx Rule Timeline." 2025. https://www.ccjdigital.com/regulations/emissions/article/15771994/epa-rejects-trucking-industry-plea-will-keep-2027-nox-rule-timeline
11. DieselNet. "USA: Nonroad Diesel Engines — Emission Standards (Tier 1-4)." 2024. https://dieselnet.com/standards/us/nonroad.php
12. U.S. Department of Justice. "United States and California Announce Diesel Engine Manufacturer Cummins Inc. Agrees to Pay a Record $1.675 Billion Civil Penalty." 2024. https://www.justice.gov/archives/opa/pr/united-states-and-california-announce-diesel-engine-manufacturer-cummins-inc-agrees
13. Heavy Duty Trucking (truckinginfo.com). "Cummins to Spend $2 billion in 'Defeat Device' Settlement." 2024. https://www.truckinginfo.com/news/cummins-to-spend-2-billion-in-defeat-device-settlement
14. Rehlko / PR Newswire. "Kohler Energy Rebrands as Rehlko; Platinum Equity majority owner (transaction closed May 2024)." 2024. https://www.prnewswire.com/news-releases/kohler-energy-rebrands-as-rehlko-302249135.html
15. KPS Capital Partners. "KPS Completes Acquisition of Briggs & Stratton (~$550M, September 2020)." 2020. https://www.kpsfund.com/news/press-releases/2020/09/22/kps-capital-partners-completes-acquisition-of-briggs-stratton-corporation
16. Business Wire. "Fairbanks Morse Defense (a portfolio company of Arcline Investment Management) — naval diesel engines." 2022. https://www.businesswire.com/news/home/20221011005272/en/Fairbanks-Morse-Defense-to-Provide-Engines-Featuring-Common-Rail-Technology-for-LPD-32
17. U.S. Census Bureau. "2022 NAICS — 333618 definition and cross-references." 2022. https://www.census.gov/naics/?details=33361&input=33361&year=2022
18. Caterpillar Inc. "Form 10-K, FY2025 (Power & Energy segment $32.2B sales, $6.4B profit; power-generation sales +32% led by data centers)." U.S. SEC, 2026. https://www.sec.gov/Archives/edgar/data/18230/000001823026000008/cat-20251231.htm
19. Brunswick Corporation. "Form 10-K, FY2025 (Propulsion segment $2.2B, 8.9% margin; Engine Parts & Accessories 18.1% margin)." U.S. SEC, 2026. https://www.sec.gov/Archives/edgar/data/14930/000001493026000027/bcorp-20251231.htm
20. U.S. EPA. "Economic impact analysis of the proposed small nonroad spark-ignition engine rule — Table 2-2 (2002 cost structure)." 2008. https://downloads.regulations.gov/EPA-HQ-OAR-2004-0008-0469/content.pdf
21. Association of Equipment Manufacturers. "Ag & Construction Equipment Markets Hope for Much-Needed Momentum in 2025." 2025. https://www.aem.org/news/ag-construction-equipment-markets-hope-for-muchneeded-momentum-in-2025
22. Association of Equipment Manufacturers. "Construction Rebounds, Agriculture Struggles as Global Shocks Mount (2026 outlook)." 2026. https://www.aem.org/news/construction-rebounds-agriculture-struggles-as-global-shocks-mount
23. National Marine Manufacturers Association. "2024 U.S. Outboard Engine Sales Report." 2025. https://www.nmma.org/press/article/25121
24. U.S. EPA. "Engine Testing Regulations — overview of rules and test procedures." 2025. https://www.epa.gov/vehicle-and-fuel-emissions-testing/engine-testing-regulations
25. U.S. EPA. "How to Obtain a Copy of a Certificate of Conformity for a Heavy-Duty or Nonroad Engine." 2025. https://www.epa.gov/importing-vehicles-and-engines/how-obtain-copy-certificate-conformity-heavy-duty-or-nonroad-engine
26. U.S. EPA. "Final Rule — Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles — Phase 3." 2025. https://www.epa.gov/regulations-emissions-vehicles-and-engines/final-rule-greenhouse-gas-emissions-standards-heavy-duty
27. California Air Resources Board. "CARB Approves Updated Regulations Requiring Most New Small Off-Road Engines Be Zero-Emission by 2024." 2021. https://ww2.arb.ca.gov/news/carb-approves-updated-regulations-requiring-most-new-small-road-engines-be-zero-emission-2024

Note on SBA size standard (1,500 employees) and quarterly payroll ($814M, Q1 2023): U.S. Small Business Administration size standards (2023) and Census County Business Patterns (2023), per ingested federal ground-truth data.