Our heavy hex bolts deliver advantages specific to high-load structural bolting: an oversized hex head that spreads clamp load over a wider bearing face, compliance with the ASTM A325 / A490 / F3125 structural bolt system, and full-set supply of matching A194 2H / A563 DH nuts with F436 hardened washers. To keep procurement simple, we back every order with free standard samples, engineer grade-selection & tensioning support, OEM / custom drawing service, material test reports with third-party inspection, flexible MOQ and worldwide shipping.
Specification of High Strength Heavy Hex Bolts
| Parameter | Options / Value |
|---|---|
| Product | High strength heavy hex bolt (large hex head structural bolt) |
| Standards | ASTM F3125 (A325 / A490) · ASTM A193 B7 / B7M · DIN 6914 · ISO 4014 / 4017 |
| Grade | A325 · A490 · B7 · Grade 8.8 / 10.9 / 12.9 |
| Tensile Strength | A325 120 ksi min · A490 150–173 ksi · 830–1220 MPa |
| Material | Carbon Steel / Alloy Steel (AISI 4140, 35CrMo, 40Cr); Stainless on request |
| Sizes | 1/2" – 2" (inch) · M16 – M48 (metric), custom available |
| Thread | UNC / UNF / Metric · full thread or partial thread |
| Head | Large hex head per ASME B18.2.1 |
| Surface Finish | Black Oxide / Zinc Plated / HDG / Dacromet / PTFE |
| Matching Hardware | A194 Grade 2H / A563 Grade DH heavy hex nuts · F436 hardened washers |
| Service Temperature | -29°C to +450°C (alloy steel B7) |
| Lead Time | Standard 7–15 days · Custom 15–25 days |
| Documents | ISO 9001 · MTR · Certificate of Origin · Inspection report |
Which Heavy Hex Bolt Should You Choose?
Heavy hex bolts fall into three product families. Match your joint and certification requirement to the right line so you don't order the wrong standard.
| Product family | Standard | Best for | Match with |
|---|---|---|---|
| Structural (inch) | ASTM A325 / A490 / F3125 | Steel structure, bridges, transmission & wind towers, base plates | A563 DH or A194 2H nut + F436 washer |
| Alloy, high-temp/pressure | ASTM A193 B7 / B7M | Petrochemical, pipeline, pressure vessels, flanged joints (-29°C ~ +450°C) | A194 2H nut |
| Metric (Euro) | DIN 6914 / EN 14399 / ISO 4014 | Euro & metric steel structures, high-strength friction-grip joints | DIN 6915 / EN 14399-4 nut |
Not sure which family fits? Send your drawing or service condition and our engineers confirm the correct grade and standard before you order.
Strength Grades & Mechanical Properties
Choose by load and safety margin. We manufacture and test every heavy hex bolt to its rated strength and document it on the material test report for each lot.
| Grade | Tensile (min) | Yield (min) | Typical use |
|---|---|---|---|
| ASTM A325 (Type 1) | 120 ksi (830 MPa) | 92 ksi (635 MPa) | Structural steel, general purpose |
| ASTM A490 | 150–173 ksi (1040 MPa) | 130 ksi (895 MPa) | High-strength structures, fatigue loads |
| Grade 8.8 / 10.9 / 12.9 | 830 / 1040 / 1220 MPa | 660 / 940 / 1100 MPa | Metric mechanical & structural assemblies |
| ASTM A193 B7 | 125 ksi (min) | 105 ksi (min) | High temperature / high pressure (Cr-Mo alloy) |
Matching nuts and washers are hardness-matched to the bolt grade for consistent clamp performance. Service temperature for alloy steel B7 ranges -29°C to +450°C.
Standards & Heavy Hex Dimension Tables
Heavy hex bolts differ from standard hex bolts by their larger head - a wider bearing face that distributes higher clamping load without crushing the joint.
Inch heavy hex bolts - key dimensions (ASME B18.2.1, inches)
| Size | Thread | Width across flats | Head height (approx.) |
|---|---|---|---|
| 5/8" | 11 UNC | 0.94 | 0.44 |
| 3/4" | 10 UNC | 1.13 | 0.50 |
| 7/8" | 9 UNC | 1.31 | 0.56 |
| 1" | 8 UNC | 1.50 | 0.63 |
| 1-1/8" | 8 UNC | 1.69 | 0.69 |
| 1-1/4" | 8 UNC | 1.88 | 0.75 |
| 1-1/2" | 6 UNC | 2.25 | 0.88 |
| 2" | 4.5 UNC | 3.00 | 1.13 |
Metric heavy hex bolts (DIN 6914 / EN 14399, across flats mm)
| Size | Pitch (mm) | Width across flats s | Head height approx. |
|---|---|---|---|
| M16 | 2.0 | 24 | 10 |
| M20 | 2.5 | 30 | 13 |
| M24 | 3.0 | 36 | 15 |
| M30 | 3.5 | 46 | 19 |
| M36 | 4.0 | 55 | 23 |
| M48 | 5.0 | 75 | 31 |
Note:dimensions follow ASME B18.2.1 / DIN 6914 / EN 14399. Exact values are re-confirmed against the current standard and your drawing before production.
Surface Finish & Corrosion Protection
We apply each coating on our controlled finishing line and verify it, so the finish protects your service life without changing the bolt's rated clamp load. Choose the protection that fits your environment below.
| Finish | Coating type | Salt-spray (approx.) | Best for |
|---|---|---|---|
| Black oxide / plain | Oxide film / oil | Low | Interior structural & where lubrication is applied |
| Zinc plated | Electroplated zinc | 48–96 h | Indoor & mild environments |
| Hot-dip galvanized (HDG) | Thick dipped zinc | Exterior long-term grade | Outdoor steel structures, bridges |
| Dacromet / zinc-flake | Zinc-aluminium flake | 500–1000 h | Coastal, high-humidity, wind towers |
Tell us the service environment - our engineers pick the finish that protects the bolt without changing its rated clamp load.
Applications of Heavy Hex Bolts
| Application | Specific joint location | Recommended |
|---|---|---|
| Steel structure | Column–beam moment joints, brace & splice plate connections, base plates | A325 / A490, HDG |
| Bridge | Girder splice connections, bearing and bracing joints | A325 / A490 |
| Transmission & wind towers | Tower flange joints, foundation anchorages, lattice leg joints | A490 / 10.9, Dacromet |
| Heavy machinery | Heavy equipment base frames, vibrating & fatigue-loaded assemblies | Grade 10.9 / 12.9 |
| Pipeline & pressure | Flanged joints, valve & pump bodies, pressure vessels (high temp) | B7, PTFE |
| Infrastructure | Retrofit & field erection, crossover equipment steelwork | A325 / A490 |
Matching Nuts & Hardened Washers
A structural bolted connection is not complete without the right nut and washer. We supply the full fastening system so hardness and load rating stay matched.
Heavy hex nuts
ASTM A194 Grade 2H / 2HM - hardened alloy nut for A490 and B7.
ASTM A563 Grade DH - hardened carbon nut for A325.
DIN 6915 / EN 14399-4 - metric structural nuts.
Hardened washers
ASTM F436 - flat, hardened washers that protect the bearing surface and spread load under the nut.
Available as load-indicating washers (DTIs) for direct tension verification.
Order bolt + nut + washer as a set - one part number, one inspection report, and a truly matched connection.
Installation & Preload for Structural Bolts
Structural heavy hex bolts are tensioned to a specified preload, not just tightened by feel.
Preload methods
Turn-of-nut - turn the nut a fixed rotation from snug.
Calibrated wrench - torque per calibrated value.
Load-indicating washers (DTIs) - visual gap confirms the bolt is tensioned.
Good-practice notes
Do not reuse structural bolts after final tensioning.
Use the matching nut grade and hardened F436 washers.
Check for oversized or slotted holes before tensioning per design.
Production Process & Quality Assurance
How we produce heavy hex bolts
| Step | Process |
|---|---|
| 1. Wire material | Certified steel with traceable heat number |
| 2. Cold heading / forging | Large hex head formed, material grain flow retained |
| 3. Heat treatment | Quench & temper for uniform hardness and rated strength |
| 4. Thread rolling | Rolled threads for accuracy and stronger grain flow |
| 5. Surface treatment | Coating applied per specification |
| 6. Inspection & testing | Tensile, hardness, proof-load and dimensional checks per lot |
| 7. Packaging & shipping | Rust-protected, packed, shipped with documents |
Quality assurance that answers buyer concerns
| Buyer concern | Our quality assurance |
|---|---|
| Is the grade genuine & traceable? | MTR with heat & batch numbers, traceable steel-to-bolt |
| Is the rated strength real? | Tensile, hardness and proof-load checks per lot |
| Does it fit the standard head? | Dimensional checks per ASME B18.2.1 / DIN 6914 |
| Does the coating protect? | Coating-thickness and salt-spray verification |
| Is every batch the same? | Lot-number tracking and inspection records |
| What if a problem occurs? | Clear warranty response; third-party inspection welcome before shipment |
Custom & OEM Heavy Hex Bolts
Non-standard sizes, special alloy grades, custom head or flange geometry, and your marking / drawing number / payoff stamp are available. Send a drawing and we confirm manufacturability and tolerance before you commit.
| Step | What happens |
|---|---|
| 1. Requirements | Send drawing or detailed spec (grade, size, material, coating, marking) |
| 2. Engineering review | Confirm manufacturability, dimensional tolerance, recommend grade / finish |
| 3. Sample | Sample produced and dimension-checked for approval |
| 4. Production | Batch production with in-process & final inspection |
| 5. Shipment | Delivered with MTR, CO and inspection report |
Packaging, Shipping & Lead Time
Every order is packed, protected and documented so it arrives traceable and ready for inspection. Our lead time and logistics terms are below.
| Item | Detail |
|---|---|
| Packaging | Plastic bags / cartons / wooden pallets; rust-protection oil or VCI paper on request |
| Standard lead time | 7–15 days for stock sizes |
| Custom lead time | 15–25 days (incl. sample confirmation) |
| MOQ | Flexible; free samples for standard items |
| Documents | Packing list, MTR, CO, inspection report |
FAQ:
What is the difference between a heavy hex bolt and a standard hex bolt?
A heavy hex bolt has a larger head (wider across flats, taller and thicker head) that spreads clamping load over a bigger bearing area - ideal for structural connections under high tension.
What does backing A325 and A490 mean?
A325 (120 ksi) and A490 (150–173 ksi) are ASTM structural bolt grades covered by ASTM F3125. We supply both Type 1 lines with matched heat treatment and test reports so your design strength is real.
Do I need special nuts and washers?
Yes. Use A563 Grade DH or A194 Grade 2H heavy hex nuts and F436 hardened washers, hardness-matched to the bolt grade. We supply bolt + nut + washer as a full set.
Which finish for outdoor steel structures?
Hot-dip galvanized (HDG) or, for coastal/high-humidity, Dacromet. Our engineers match the finish to your service environment.
Do you supply material test reports?
Yes. MTR with heat and batch numbers are available, and third-party inspection is welcome before shipment.
