Our high tensile flange bolts deliver three core advantages: a one-piece flange that acts as a built-in washer for a larger bearing area and more even preload, a serrated option that resists loosening under vibration, and tested mechanical properties across grades 8.8 / 10.9 / 12.9. To keep procurement simple, we back every order with free standard samples, engineer design support, OEM / custom drawing service, material test reports with third-party inspection, flexible MOQ and worldwide shipping.
Comprehensive Specification of High Tensile Flange Bolts
| Parameter | Options / Value |
|---|---|
| Sizes (M × Pitch) | M5×0.8 / M6×1.0 / M8×1.25 / M10×1.5 / M12×1.75 / M16×2.0 / M20×2.5 / M24×3.0 / M30×3.5 |
| Strength Grade | 8.8 / 10.9 / 12.9 |
| Tensile Strength | 830 / 1040 / 1220 MPa |
| Material | Carbon Steel / Alloy Steel (40Cr, 35CrMo); Stainless Steel on request |
| Thread | Full thread / partial thread · tolerance 6g / 6h |
| Standards | DIN 6921 / ISO 4162 / EN 1665 / JIS B1189 / EN 14399 |
| Surface Finish | Zinc Plated / HDG / Dacromet / Black Oxide / Plain |
| Flange Type | Serrated / non-serrated |
| Length | Standard or custom per drawing |
| Lead Time | Standard 7–15 days · Custom 15–25 days |
| MOQ | Flexible · free samples for standard items |
| Documents | ISO 9001 · MTR · Certificate of Origin · Inspection report |
What Makes a Flange Bolt Different?
The integrated flange under the hex head acts as a built-in washer. Instead of a separate flat washer, the flange spreads clamping force over a larger bearing area - so the bolt delivers more even, controlled preload and works reliably under vibration and heavy dynamic loading.
Integrated flange = built-in washer
The enlarged bearing face distributes clamp load over more surface, prevents crushing of softer or thin-walled materials, and eliminates one assembly step on your production line.
Serrated vs non-serrated
Serrated flange bolts bite into the mating surface under torque, resisting loosening in vibration-prone joints; non-serrated versions protect soft or smooth bearing surfaces.
How it behaves better than hex bolt + washer
| Dimension | High tensile flange bolt | Hex bolt + separate washer |
|---|---|---|
| Clamp-load spreading | One-piece larger bearing face | Smaller bearing, depends on washer placement |
| Assembly steps | One step, no washer | Two steps (bolt + washer) |
| Vibration loosening | Serrated option bites into the face | Lower inherent resistance |
| Bearing-surface crushing | Larger area = less risk | Concentrated-area risk |
| Preload control | More even and controlled | More variable |
Because the flange and head are forged as one piece, the load path and preload are predictable - the reason high tensile flange bolts hold better on vibrating steel and machinery joints.
Flange Bolt Grades & Mechanical Properties
Choose by load and safety margin. We manufacture to tested mechanical properties so you can trust the rated strength, not just the grade stamping.
| Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Typical Use |
|---|---|---|---|
| 8.8 | 830 | 660 | General structural and mechanical assemblies |
| 10.9 | 1040 | 940 | Steel structures, wind towers, heavy machinery |
| 12.9 | 1220 | 1100 | Demanding static & fatigue load applications |
Note:materials include carbon steel and alloy steel (40Cr, 35CrMo, SCM435 equivalent), each quenched & tempered for consistent hardness. Stainless steel grades are available on request for corrosion-critical projects.
Standards & Dimensions
We manufacture to the flange-bolt standards your design specifies, with controlled thread tolerance and flange geometry.
| Standard | Scope |
|---|---|
| DIN 6921 | Hex flange bolts, metric |
| ISO 4162 | Hexagon bolts with flange, metric |
| EN 1665 | Hexagon bolts with flange (washer-faced head), heavy series |
| JIS B1189 | Hex flange bolts, Japanese standard |
| EN 14399 | High-strength structural bolting assemblies (where applicable) |
Note:Size range M5 – M30. Full or partial thread, standard thread tolerances 6g / 6h. Non-standard sizes and specialized head/flange geometry are available as custom flange bolts.
Flange bolt dimension table (ISO 4162 / DIN 6921, metric, mm)
| Size (M×P) | Width across flats s | Head height k | Flange dia. dc | Bearing dia. dw |
|---|---|---|---|---|
| M5×0.8 | 8 | 5.6 | 11.8 | 9.3 |
| M6×1.0 | 10 | 6.6 | 14.2 | 11.3 |
| M8×1.25 | 13 | 8.1 | 17.0 | 14.3 |
| M10×1.5 | 16 | 10.0 | 20.8 | 17.6 |
| M12×1.75 | 18 | 12.0 | 24.7 | 21.5 |
| M16×2.0 | 24 | 16.0 | 32.5 | 28.7 |
| M20×2.5 | 30 | 20.0 | 40.3 | 35.9 |
| M24×3.0 | 36 | 24.0 | 47.8 | 43.3 |
| M30×3.5 | 46 | 30.0 | 59.6 | 54.2 |
Note:dimensions above follow ISO 4162 / DIN 6921. Exact values are re-confirmed against the current standard and your drawing before batch production.
Surface Finish & Corrosion Protection
Pick the finish that matches your service environment - outdoor steel structures, marine, chemical or indoor assemblies.
| Finish | Coating type | Salt-spray (approx.) | Best for |
|---|---|---|---|
| Zinc plated | Electroplated zinc | 48–96 h | Indoor & mild environments; clear / blue / yellow |
| Hot-dip galvanized (HDG) | Thick dipped zinc | Exterior long-term grade | Outdoor, high-humidity, steel structure |
| Dacromet / Zinc-flake | Zinc-aluminium flake | 500–1000 h | Automotive, chemical exposure |
| Black oxide | Oxide film | Low | Interior mechanical use |
| Plain | Oil film only | - | Where in-field lubrication is preferred |
Tell us your environment and coating requirement - our engineers recommend the finish that protects your flange bolts without compromising clamp ability.
Applications of High Tensile Flange Bolts
| Application | Specific joint location | Recommended |
|---|---|---|
| Steel structure | Column–beam moment & bracing joints, purlin-to-rafter, stair & platform brackets | Grade 8.8–10.9, HDG |
| Wind power | Tower flange connections, blade–hub studs, foundation anchor plate | Grade 10.9–12.9, Dacromet |
| Machinery | Vibrating screens, conveyor tensioning, heavy equipment base frames | Grade 8.8–10.9 |
| Automotive | Chassis suspension, engine / transmission mounts | Grade 10.9, zinc-flake |
| Piping & valves | Flange joints under pressure, pump-valve bodies, pressure vessels | Grade 8.8–10.9 |
| Railway | Fish-plate joints, signal equipment, catenary mast bases | Grade 10.9, HDG |
How We Produce High Tensile Flange Bolts
Every production step is controlled so the flange, thread and heat treatment consistently meet your rated grade.
| Step | Process |
|---|---|
| 1. Wire material | Source certified steel with a traceable heat number |
| 2. Cold heading / forging | Head and flange formed as one piece |
| 3. Heat treatment | Quench & temper for uniform hardness and strength |
| 4. Thread rolling | Rolled threads for stronger grain flow and accuracy |
| 5. Surface treatment | Coating applied per your finish requirement |
| 6. Inspection & testing | Hardness, tensile and dimensional checks per lot |
| 7. Packaging & shipping | Rust-protected, packed and shipped with documents |
Quality Assurance & Material Traceability
Every lot is traceable. Material test reports (MTR) are available, and flange bolts undergo lot-controlled inspection before shipment.
Quality assurance that answers buyer concerns
| Buyer concern | Our quality assurance |
|---|---|
| Is the material genuine & traceable? | MTR with heat & batch numbers, traceable from steel to finished bolt |
| Is the rated strength real? | Hardness, tensile, proof-load and clamp checks per lot |
| Are dimensions consistent? | Lot-controlled dimensional checks with controlled thread tolerance |
| Does the coating really protect? | Coating-thickness and salt-spray verification |
| Is every batch the same? | Lot-number tracking and 100% inspection record |
| What if a problem occurs? | Clear warranty response; third-party inspection welcome before shipment |
Our Custom Flange Bolts & OEM Service
When a standard DIN / ISO flange bolt doesn't match your drawing or service condition, we manufacture custom flange bolts to spec - from a single test sample to large OEM runs, with the same dimensional control and traceability.
What you can customize
Non-standard M-size & length
Special materials & grades
Custom flange geometry
Thread type / tolerance
Surface & coating
Head style
Your marking / logo / drawing number
Why custom flange bolts help
Fit the exact bearing load of your joint
Comply with a project or client specification
Anti-counterfeit marking & easy on-site identification
Remove the compromise of "closest standard"
Customization process
| Step | What happens |
|---|---|
| 1. Requirements | Send your drawing or detailed spec (grade, size, material, coating, marking) |
| 2. Engineering review | We confirm manufacturability, dimensional tolerance and suggest the best grade / finish |
| 3. Sample | Sample produced and dimension-checked for your approval |
| 4. Production | Batch production with in-process and final inspection |
| 5. Shipment | Delivered with MTR, CO and inspection report |
Packaging, Shipping & Lead Time
| Item | Detail |
|---|---|
| Packaging | Plastic bags / cartons / wooden pallets; rust-protection oil or VCI paper on request |
| Standard lead time | 7–15 days for standard flange bolts |
| Custom lead time | 15–25 days (incl. sample confirmation) |
| Shipping | Sea / air freight; FOB / CIF / DDP terms |
| MOQ | Flexible; free samples for standard items |
| Documents | Packing list, MTR, certificate of origin, inspection report |
FAQ:
Do flange bolts need a separate washer?
No. The integrated flange under the head acts as a built-in washer, spreading clamp load over a larger bearing area. High tensile flange bolts are typically installed without a separate washer, which also simplifies assembly on production lines.
What is the difference between serrated and non-serrated flange bolts?
Serrated flange bolts have teeth that bite into the mating surface under torque, providing extra resistance to loosening in vibration-prone joints. Non-serrated versions are preferred where the bearing surface must not be scratched, such as on softer materials.
Which grade should I choose - 8.8, 10.9 or 12.9?
Choose by load and safety margin. Grade 8.8 suits general structural and mechanical use; 10.9 and 12.9 deliver higher tensile strength for demanding static and fatigue loads in steel structures and heavy machinery. Our engineers help verify with proof-load checks.
Are DIN 6921, ISO 4162 and EN 1665 the same?
They are similar flange-head bolt standards with minor dimensional differences. DIN 6921 and ISO 4162 define hex flange bolts, EN 1665 covers washer-faced flange head bolts. Specify the standard your design requires and we manufacture to that tolerance.
Do you supply material test reports and testing?
Yes. Material test reports (MTR) are available, and our flange bolts undergo lot-controlled inspection with hardness, tensile and coating checks. Third-party inspection is welcome before shipment.
