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China Suppliers Hex Flange Bolt DIN6921 Yellow Zinc Plated Factory Supply - Carbon Steel & Alloy Options Available
Flange bolt, also known as flange bolt, is a special type of bolt with a flange surface (flange), widely used in situations that require high preload, anti-loosening, and sealing.
Structural Characteristics
Flange Surface Design
There is an integral flange (circular gasket) below the bolt head, which increases the contact area, disperses pressure, and reduces damage to the connection surface.
Hexagonal or Twelve-Pointed Head
Commonly designed as a hexagonal head, easy to tighten with standard tools. Some high-strength models use twelve corner heads.
Anti-Slip Tooth Pattern
The flange surface of some flange bolts has radial tooth patterns to enhance friction and prevent loosening.
Main Advantages
No Additional Gaskets Needed
The integrated flange replaces traditional gaskets, simplifies installation steps, and reduces costs.
Anti-Vibration & Anti-Loosening
The flange surface increases friction, and the tooth pattern design further prevents bolts from loosening in vibration environments.
Uniform Force Distribution
The flange disperses the load, protects the surface of the connected parts, and avoids crushing or deformation.
Sealing Enhancement
When combined with flange surfaces and soft materials such as rubber gaskets, the sealing performance can be improved.
Common Application Areas
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Automotive Industry
Key parts such as engine, gearbox, and wheel hub — adapted to high vibration environments.
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Machinery Manufacturing
Heavy equipment, machine tools, pumps, valves, and other connections requiring high preload force.
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Architecture & Steel Structures
Wind and earthquake-resistant structures such as bridges, steel frames, and curtain walls.
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Rail Transit
Rail vehicles and signal equipment — scenarios with high requirements for safety and reliability.
Material & Surface Treatment
| Category | Type | Description |
|---|---|---|
| Common Materials | Carbon Steel | Grade 4.8, 8.8, 10.9 — general-purpose strength levels |
| Stainless Steel | A2-304, A4-316 — corrosion-resistant applications | |
| Alloy Steel | High-strength or high-temperature resistant environments | |
| Surface Treatment | Galvanized | Conventional anti-corrosion protection |
| Dacromet | High corrosion resistance coating | |
| Hot-Dip Galvanizing | Heavy-duty anti-corrosion, suitable for outdoor use | |
| Phosphating | Enhances wear resistance and adhesion |
Frequently Asked Questions
QWhat is the main difference between a flange bolt and a standard bolt?
A flange bolt features an integrated flange (circular washer) beneath the bolt head. This eliminates the need for a separate washer, increases the bearing surface area, distributes clamping load more evenly, and provides better resistance to loosening compared to a standard bolt.
QDo flange bolts require a separate washer during installation?
No. The integrated flange on the bolt head serves the same function as a traditional washer. This simplifies the installation process, reduces the number of components needed, and lowers overall assembly costs.
QWhich material grade of flange bolt is best for high-vibration environments?
For high-vibration environments such as automotive engines or heavy machinery, Grade 10.9 carbon steel or alloy steel flange bolts with serrated (toothed) flange surfaces are recommended. The tooth pattern significantly increases friction and prevents the bolt from loosening under vibration.
QWhat surface treatment should I choose for outdoor or corrosive environments?
For outdoor or highly corrosive environments, hot-dip galvanizing or Dacromet coating is recommended. Hot-dip galvanizing provides a thick zinc layer suitable for heavy-duty outdoor applications, while Dacromet offers excellent resistance to salt spray and chemical corrosion without hydrogen embrittlement risk.
QCan flange bolts be reused after removal?
Flange bolts can generally be reused if they show no signs of deformation, thread damage, or wear on the flange surface. However, high-strength bolts (Grade 10.9 or above) that have been torqued to their yield point should be replaced after removal to ensure joint integrity and safety.
QWhat is the difference between a serrated flange bolt and a smooth flange bolt?
A serrated (toothed) flange bolt has radial grooves on the flange surface that bite into the mating surface, providing superior anti-loosening performance — ideal for vibration-prone applications. A smooth flange bolt has a flat flange surface, which is better suited for softer or coated materials where surface damage must be minimized.