Heavy Hex Bolt (ASME B18.2.1 / DIN 6914)
Heavy hex bolts have a thicker head and larger across-flats dimension than standard hex bolts of the same nominal diameter. The increased bearing surface distributes clamping load more effectively and tolerates higher tightening torque, which is why heavy hex is the standard form for large structural and high-temperature/high-pressure applications.
Specifications
| Standards | ASME B18.2.1 heavy series, DIN 6914 (DIN HV) |
|---|---|
| Diameter Range | 1/2" – 3" (M12 – M64 in DIN 6914) |
| Property Class | A307, Grade 5, Grade 8 (inch); 8.8, 10.9 (metric DIN HV) |
| Head Dimensions | Thicker head and larger AF compared to standard hex bolts |
| Surface Finish | Plain, HDG, Zinc plated |
Frequently Asked Questions
When is a heavy hex bolt preferred over a standard hex bolt?
Use heavy hex when you need a larger bearing surface under the head (heavy clamping load on a soft or thin mating surface), when high torque is applied during installation, or when local code or specification calls it out. Heavy hex is also standard for many petrochemical and power generation applications.
Are heavy hex bolts the same as heavy hex structural bolts?
No. A heavy hex bolt is a general-purpose bolt with heavy hex head dimensions. A heavy hex structural bolt — typically ASTM A325 or A490 — is a specific high-strength bolt for steel-to-steel structural connections, with shorter thread length and very tight controls on mechanical properties. They look similar but are not interchangeable in structural specifications.
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