Flange Bolt
Bolts · flange head bolt · frame bolt · serrated flange bolt
Definition: A flange bolt is a hex bolt with an integrated washer-like flange under the head that spreads load and resists loosening — no separate washer needed.
Anatomy
■ Head■ Shank■ Threads■ Point
Governing standards: ASME B18.2.1 · DIN 6921
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/4-20 | M6 x 1.0 | 1/2 flange | 5/16 |
| 3/8-16 | M10 x 1.5 | 11/16 flange | 7/16 |
| 1/2-13 | M12 x 1.75 | 7/8 flange | 9/16 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Grade 5 / 8.8 | medium carbon steel, Q&T | 120,000 | 3 radial lines |
| Grade 8 / 10.9 | alloy steel, Q&T | 150,000 | 6 radial lines |
Materials
- Zinc-plated steel
- Stainless steel
- Hot-dip galvanized steel
Pros & Cons
Pros
- Built-in washer — saves a part
- Serrated flange resists vibration
- Spreads load over a larger area
Cons
- Needs wrench clearance around the flange
- Pricier than a plain hex bolt
- Serrated flange can mar painted surfaces
Typical Uses
- Automotive and engine assembly
- Machinery and equipment
- Frame and chassis joints
Alternatives & Related
- Hex Bolt — Plain bolt when you are already using a washer
- Flange Nut — The matching nut-side option with a flange
Where to Buy
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FAQ
Flange bolt vs hex bolt?
A flange bolt has a washer built into the head, so it distributes load without a separate washer and is common in automotive work. A hex bolt needs a separate washer.
Where are flange bolts used?
Engines, transmissions, and machinery, where the integrated flange speeds assembly and resists vibration loosening.