In addition, we produce these high strength structural bolts to meet ASTM F3125 (covering Grades A325 and A490), ASTM A325M/A490M metric grades, and EN 14399 (System HR and HV). Therefore, engineers and contractors rely on them for critical load-bearing connections in steel bridges, high-rise buildings, transmission towers, and industrial infrastructure.

Standard Specifications — ASTM F3125 & EN 14399 Heavy Hex Bolts

To begin with, we manufacture our heavy hex structural bolts to two major global standards. The table below compares their key specifications so you can select the right bolts for your project.

Material & Dimensional Standards for Structural Bolts

• To begin with, we use medium carbon steel and alloy steel as the base material for all heavy hex bolts.
• Moreover, we conform to ASME B18.2.6 for heavy hex structural bolt dimensions (inch series) and EN 14399-3/-4 for metric HV/HR systems.
• Additionally, we match bolts with ASTM A563/A563M heavy hex nuts and ASTM F436/F436M hardened washers to form complete structural bolt assemblies.
• For special orders, we supply weathering steel (Type 3) bolts for atmospheric corrosion resistance without coating.
• Finally, we offer OEM & ODM — we customize bolt diameter, length, thread pitch, head marking, and packaging according to your drawings or project specifications.

Corrosion Protection — HDG, Geomet & F3393M Class G Coating

In fact, coating selection is critical for heavy hex structural bolts in bridge and outdoor applications. Furthermore, we offer three coating systems to match different project requirements.

Hot Dip Galvanized (HDG) — ASTM F2329

• First, we hot dip galvanize our structural bolts to ASTM F2329, the standard specification for zinc coating applied to carbon and alloy steel bolts.[reference:4]
• Second, we achieve a minimum coating thickness of 0.0020 in. (50 μm) for fasteners over 3/8″ in diameter.[reference:5]
• Third, HDG provides excellent outdoor corrosion protection for steel bridge and infrastructure applications.[reference:6]
• However, HDG is not suitable for A490 bolts due to hydrogen embrittlement risk from the pickling process.[reference:7]

Geomet / Zinc Flake Coating — ASTM F3393M Class G

• To begin with, Geomet is a non-electrolytically applied zinc/aluminum flake coating that provides superior corrosion resistance.[reference:8]
• Moreover, ASTM F3393M Class G specifies a minimum salt spray resistance of 1,000 hours.[reference:9]
• Most importantly, Geomet coating does not promote environmental hydrogen embrittlement (EHE) on ASTM A490 heavy hex bolts, making it the preferred coating for high-strength A490 applications.[reference:10]
• Therefore, we recommend Geomet for A490 structural bolts in steel bridge projects where both high strength and corrosion resistance are required.

Coating Selection Guide

About Our Factory — Direct Manufacturer of Heavy Hex Structural Bolts

In fact, Tarco Industry operates a modern manufacturing facility and we dedicate it to the production of heavy hex structural bolts, tension control bolts, and high strength structural fasteners. Furthermore, we complete every step — from raw material selection to forging, heat treatment, coating, and packaging — in our own factory. Consequently, we do not outsource production, and we do not act as a middleman.

In addition, we equip our factory with advanced hot forging machines, automated thread rolling lines, continuous heat treatment furnaces, and strict quality inspection systems. As a result, we produce ASTM F3125 heavy hex bolts and EN 14399 structural bolting assemblies with consistent mechanical properties, reliable dimensional accuracy, and stable performance for B2B customers worldwide. Therefore, whether you need standard bolts or custom specifications, Tarco Industry can produce them directly for you.

Factory Direct Advantages

• First, we are a Manufacturer, Not a Trader — you buy directly from Tarco Industry production lines, and we eliminate middleman markups.
• Second, we handle In-House Production — we produce bolts, nuts, and washers all under one roof for full quality control.
• Third, we welcome OEM & ODM — we customize bolt dimensions, material grades, coatings, and head markings according to your project specifications.
• Fourth, we maintain Bulk Production Capacity — we ensure stable output for large steel bridge and infrastructure orders with short lead times.
• Finally, we provide Factory Price — we offer competitive direct pricing for distributors, EPC contractors, and steel structure fabricators.

Why Choose Our Heavy Hex Structural Bolts?

• For example, our bolts offer High Tensile Strength — A325 provides 120 ksi minimum and A490 provides 150 ksi minimum, meeting the most demanding steel bridge connection requirements.[reference:11]
• In addition, they feature Larger Bearing Surface — the heavy hex head design distributes load over a wider area than standard hex bolts, which is essential for structural steel connections.[reference:12]
• Moreover, they support Preloading Capability — EN 14399 HR and HV systems allow preloading of at least 0.7 times the bolt’s minimum tensile strength, ensuring joint integrity under dynamic loads.[reference:13]
• Furthermore, we offer Full Traceability — every production batch includes material certificates, heat treatment records, and mechanical test reports.
• As a result of their Complete Assembly Design, we supply bolts with matched nuts and washers to guarantee compatibility and avoid field installation problems.[reference:14]
• Finally, we provide Direct Factory Support — Tarco Industry provides technical guidance, samples, and custom production for your specific steel bridge bolting needs.

How to Install Heavy Hex Structural Bolts

1. First, verify the assembly — confirm that you have the correct bolt grade, nut grade, and washer type for your project specification.
2. Then, prepare the joint surfaces — clean the steel surfaces and remove any burrs or debris that could affect the friction coefficient.
3. Next, insert the bolts — place the bolts through the aligned holes with washers under the turned element (nut or bolt head, per project specification).
4. After that, tighten to the specified preload — use a calibrated torque wrench or hydraulic tensioner to achieve the required clamping force.
5. Finally, verify the installation — check that the bolts meet the specified minimum tension and mark them for inspection records.

Applications & Industries for Heavy Hex Structural Bolts

• For instance, in steel bridge construction, contractors use our bolts for main girder connections, crossbeam fastening, and bearing assemblies.[reference:15]
• Also, in high-rise buildings, they secure steel beam-to-column connections and moment frames requiring precise torque control.
• In addition, for transmission towers and power infrastructure, our bolts handle the high wind and seismic loads of lattice steel structures.
• Lastly, in industrial plants and heavy equipment, they fasten structural steel frameworks, crane rails, and equipment foundations.

Quality Assurance & Certifications

Furthermore, Tarco Industry manufactures our heavy hex structural bolts under strict quality control systems, and they comply with relevant industry standards including ASTM F3125, ISO 13918, and EN 14399. As a result, we perform dimensional inspection, tensile testing, hardness testing, and coating verification on every production batch before shipment from our factory.

• Additionally, we offer certifications including ISO 9001, CE, and SGS.
• Moreover, our production capacity reaches 500 tons per month for heavy hex bolts.
• Also, we set the MOQ at 5 tons (negotiable for sample orders).
• In terms of packaging, we offer bulk cartons on pallets or wooden crates, with custom marking available.
• Finally, we deliver within 20–30 business days after order confirmation.
• Most importantly, Tarco Industry is the manufacturer — we handle direct factory production.