DIN 931 vs DIN 933: Full Thread vs Partial Thread Hex Bolts
Technical comparison of DIN 931 (partial thread) and DIN 933 (full thread) hexagon head bolts, including thread configuration differences, grip length considerations, shear plane implications, and application selection guidance.
Thread Configuration Differences
DIN 933: Full Thread
DIN 933 specifies hexagon head bolts with full thread along the entire shank length. Threads extend from immediately below the head to the end of the bolt, providing uniform thread engagement regardless of clamping length.
DIN 931: Partial Thread
DIN 931 specifies hexagon head bolts with partial thread. The threaded portion is shorter than the shank length, leaving an unthreaded shank section between the head and threaded area. Thread length is standardized based on bolt diameter and length.
Both standards share identical head dimensions (width s, height k) and thread specifications (pitch, thread form), differing only in thread length configuration.
Grip Length Considerations
Grip length refers to the thickness of material being clamped. Thread configuration affects how bolts accommodate different grip lengths:
- •DIN 933 (Full Thread) – Accommodates variable grip lengths more easily, as threads are available along the entire shank. Suitable when clamping thickness may vary or when simplified installation is preferred.
- •DIN 931 (Partial Thread) – Requires careful selection to ensure the unthreaded shank section is within the grip length. The unthreaded portion should be in the clamped area for optimal load distribution.
Shear Plane Considerations
Thread configuration affects shear plane location and strength characteristics:
DIN 931 (partial thread) provides an unthreaded shank section that can offer higher shear strength in the unthreaded area, as the full cross-sectional area of the shank resists shear loads. This is advantageous in applications where shear loads are significant.
DIN 933 (full thread) ensures consistent load distribution along the entire length, but threads may be the weakest point under shear loading. The threaded area has reduced cross-sectional area compared to the unthreaded shank.
Comparison Table
| Aspect | DIN 933 (Full Thread) | DIN 931 (Partial Thread) |
|---|---|---|
| Thread Configuration | Full thread along entire shank | Partial thread, unthreaded shank section |
| Typical Applications | Variable clamping lengths, uniform load distribution | High shear load, longer unthreaded shank required |
| Grip Length Flexibility | High flexibility, accommodates variable thickness | Requires matching grip length to unthreaded section |
| Shear Strength | Threads may be weakest point | Higher in unthreaded shank area |
| Common Mistakes | Using when high shear strength required | Using when variable clamping lengths expected |
| Selection Cues | Short clamping length, simplified installation | High shear load, structural connections |
Assembly Implications
Thread configuration affects assembly procedures and installation considerations:
- •DIN 933 (Full Thread) – Simplified installation as threads are available along the entire length. Suitable for applications where clamping thickness may vary or where quick assembly is preferred.
- •DIN 931 (Partial Thread) – Requires careful bolt length selection to ensure the unthreaded shank section is properly positioned within the clamped area. The unthreaded portion should not extend beyond the grip length.
When NOT to Use DIN 933
DIN 933 (full thread) may not be suitable in the following scenarios:
- •Applications requiring high shear strength in the shank area, where the unthreaded section of DIN 931 provides better load distribution
- •Structural connections where the unthreaded shank section is specifically required for load transfer
- •Applications where project specifications explicitly require DIN 931 or partial thread configuration
- •Long bolts where the unthreaded shank section provides better resistance to bending loads
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Frequently Asked Questions
What is the main difference between DIN 931 and DIN 933?
DIN 931 specifies hexagon head bolts with partial thread (threaded portion shorter than shank length), while DIN 933 specifies full-threaded hexagon head bolts (threads extend along entire shank). The choice depends on application requirements, grip length, and load distribution needs.
When should I use DIN 933 instead of DIN 931?
DIN 933 (full thread) is suitable when uniform thread engagement is required, variable clamping lengths are expected, or when simplified installation is preferred. DIN 931 (partial thread) is preferred when higher shear strength is needed or when the unthreaded shank provides better load distribution.
Does thread configuration affect bolt strength?
Thread configuration affects load distribution and shear plane location. DIN 931 (partial thread) provides an unthreaded shank section that can offer higher shear strength in the unthreaded area. DIN 933 (full thread) ensures consistent load distribution along the entire length but threads may be the weakest point.
Can DIN 931 and DIN 933 bolts be used interchangeably?
While both standards share the same head dimensions and thread specifications, they are not directly interchangeable due to thread length differences. Selection should be based on application requirements, grip length, and load characteristics. Project-specific requirements may specify one standard over the other.
What are common mistakes when selecting between DIN 931 and DIN 933?
Common mistakes include using DIN 933 when higher shear strength is required (should use DIN 931), using DIN 931 when variable clamping lengths are expected (should use DIN 933), and not considering grip length requirements when selecting thread configuration.
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