Hex Bolt, Partial Thread (DIN 931 / ISO 4014)
A partially threaded hex bolt has a smooth (unthreaded) shank under the head, with threads only on the lower portion. DIN 931 and ISO 4014 are the two most common specifications. The smooth shank provides higher shear capacity than threaded shank, which is why partial-thread bolts are specified for connections subject to lateral load.
Specifications
| Standards | DIN 931, ISO 4014, ANSI/ASME B18.2.1, JIS B 1180 |
|---|---|
| Property Class | 4.8, 5.8, 8.8, 10.9, 12.9 |
| Diameter Range | M6 – M64 (1/4" – 2-1/2") |
| Length Range | 20 mm – 300 mm (longer on request) |
| Thread Length | Per standard formula (varies with diameter and length) |
| Material | Carbon steel, Alloy steel (35CrMo, 42CrMo for 10.9/12.9) |
| Surface Finish | Plain, Zinc plated, HDG, Black oxide, Dacromet |
Frequently Asked Questions
Why does a partial-thread bolt provide higher shear capacity?
The smooth shank of a partial-thread bolt has a larger cross-sectional area than the same nominal diameter at the thread root. When the bolt is loaded in shear (e.g., across a joint that wants to slide), the shear plane should ideally pass through the smooth shank rather than through the threads — the smooth shank can carry meaningfully higher shear load before yielding.
How long should the smooth shank be?
For DIN 931 and ISO 4014, the standards define a thread length formula based on bolt diameter and total length. For most general engineering, the smooth shank should be at least equal to the thickness of the unthreaded plate the bolt passes through, plus enough thread to engage a full nut. If you need a specific shank-to-thread ratio, specify the bolt as a custom length.
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