| Feature | DIN 933 (Full Thread) | DIN 931 (Partial Thread) |
|---|---|---|
| Threading | Threaded up to the underside of the head | Partial thread with an unthreaded shank |
| Grip Length | Variable (threads grip the material) | Fixed (unthreaded shank spans the joint) |
| Shear Strength | Lower (threads create stress risers in the shear plane) | Maximum (solid shank absorbs shear forces) |
| Usage Scenario | Tapped holes, general fastening, thin materials | Heavy structural joints subject to lateral movement |
| Availability | Commonly stocked in all sizes | More common in longer lengths (usually >30mm) |
The Verdict
For load-bearing structural joints subject to shear forces (sideways movement), always use DIN 931 and ensure the unthreaded shank sits across the shear plane. For general fastening or threading into a tapped hole, DIN 933 is more versatile.
Frequently Asked Questions
Is a fully threaded bolt weaker?
In tension, they are similar, but in shear, the threads of a DIN 933 bolt reduce the cross-sectional area and create stress concentration points, making it significantly weaker against sideways forces.