The DIN 933 hexagon head bolt is one of the most widely used fasteners in modern industrial and structural applications. Defined by its full thread along the entire shank and hexagonal head design, this bolt is the go-to choice for engineers, maintenance professionals, and procurement specialists who need reliable, high-strength fastening across a broad spectrum of applications.
This guide covers everything you need to know about DIN 933 bolts—from their defining features and material grades to size ranges, surface finish options, and critical selection criteria.
1. What Is a DIN 933 Bolt?
The DIN 933 standard specifies a hexagon head bolt with metric thread cut along its entire shank length. Unlike its counterpart DIN 931 (which has a partial thread with an unthreaded shank under the head), the full-thread configuration of DIN 933 ensures thread engagement begins immediately beneath the bolt head.
Key Characteristics
Full thread: Threads run the entire length of the shank—no smooth shank section
Hexagon head: Designed for external wrench drive
Metric coarse thread: Standard for most sizes (fine threads available on request)
Product grades: Grade A (M1.6–M24, lengths ≤ 10d or 150mm) and Grade B (above M24 or lengths exceeding these limits)
DIN 933 vs. DIN 931: The Critical Difference
The fundamental difference is thread length:
| Feature | DIN 933 | DIN 931 |
|---|---|---|
| Thread | Full thread entire shank | Partial thread (smooth shank under head) |
| Shear capacity | Lower (thread root stress concentration) | Higher (smooth shank is stronger) |
| Best for | Thin flanges, tapped blind holes, maximum thread engagement | Shear-load applications, structural connections |
The DIN 933 standard has been largely superseded by the international standard ISO 4017, which describes a bolt of analogous construction—hexagon head with full thread. However, DIN 933 remains widely used in specifications and product catalogs globally.
2. Material Grades and Strength Classes
DIN 933 bolts are available in multiple material grades to match different strength and corrosion-resistance requirements.
Carbon Steel Grades
| Grade | Tensile Strength | Typical Finish | Applications |
|---|---|---|---|
| 8.8 | ≥800 MPa | Black oxide, zinc plated, HDG | General industrial, standard structural |
| 10.9 | ≥1,000 MPa | Black oxide, zinc plated | High-strength critical joints |
| 12.9 | ≥1,220 MPa | Black oxide (preferred) | Ultra-high-strength applications |
Grade 8.8 is considered the entry point for "high-strength" fasteners in many industries, commonly used in general machinery, mechanical engineering, and instrumentation. Grade 10.9 is specified for critical joints in automotive, heavy equipment, and high-load structural connections.
Stainless Steel Grades
| Grade | Tensile Strength | Corrosion Resistance | Equivalent |
|---|---|---|---|
| A2-70 | ≥700 MPa | Moderate | 18-8 / 304 stainless |
| A4-80 | ≥800 MPa | Superior (marine-grade) | 316 stainless |
A2 stainless steel (equivalent to 18-8 or 304) is the standard choice for general corrosion-resistant applications. A4 (316 stainless) offers enhanced resistance to chlorides and chemicals, making it the preferred choice for marine and chemical processing environments.
3. Size Range and Availability
DIN 933 bolts are available in a comprehensive range of sizes to suit virtually any industrial application.
Diameter Range
| Property | Range |
|---|---|
| Minimum diameter | M4 (commonly stocked) |
| Maximum diameter | M64 (available for mass production) |
| Typical stocked range | M4 – M30 |
Length Range
Standard lengths: 10mm – 500mm
Custom lengths: Available on request for larger orders
Thread Pitches (Coarse Metric Standard)
| Size | Pitch (mm) |
|---|---|
| M4 | 0.7 |
| M5 | 0.8 |
| M6 | 1.0 |
| M8 | 1.25 |
| M10 | 1.5 |
| M12 | 1.75 |
| M14 | 2.0 |
| M16 | 2.0 |
| M20 | 2.5 |
| M24 | 3.0 |
| M30 | 3.5 |
Thread tolerance: Grade 8.8 and 10.9 plain finish use 6g; plated finishes use 6h; stainless steel uses 6g.
4. Surface Finish Options
Surface finish affects corrosion resistance, appearance, and—critically—hydrogen embrittlement risk for high-strength grades.
| Finish | Corrosion Resistance | H₂ Embrittlement Risk | Best For |
|---|---|---|---|
| Black Oxide | Low | None | General industrial, dry environments |
| Zinc Plated | Moderate | High (baking required for ≥8.8) | Indoor applications with moisture exposure |
| Hot-Dip Galvanized | High | Very low | Outdoor, bridges, heavy infrastructure |
| Plain (uncoated) | None | None | Controlled environments, secondary finishing |
Important note: Zinc-plated high-strength bolts (Grade 8.8 and above) carry significant hydrogen embrittlement risk. Post-plating baking at 190–210°C for 4–24 hours is mandatory to mitigate this risk. For critical applications, consider Dacromet (zinc-aluminum coating) which provides corrosion protection without hydrogen embrittlement.
5. Key Applications
DIN 933 full-thread bolts are specified across a wide range of industries due to their versatility and reliability.
Mechanical Engineering and Instrumentation
Machine frame assembly
Heavy equipment mounting
Instrumentation and control panel fastening
Oil & Gas and Marine
Pump baseplates and compressor frames
Heat exchanger shell flanges
Generator mounting brackets
Marine engine room machinery
Steel and Structural Connections
Bridge construction
Steel structure joints
High-vibration environments near railways or heavy machinery
General Industrial
Thin-gauge mounting flanges
Pre-tapped blind holes
Assemblies requiring maximum thread engagement within limited thickness
Pro tip: Full-thread DIN 933 bolts are particularly well-suited for connections where the total thickness of joined elements is relatively small and does not require a smooth shank section. However, if the bolt is expected to work in shear across the shank, a DIN 931 partial-thread bolt should be specified instead.
6. Critical Installation Notes
Minimum Thread Engagement
General engineering practice requires that at least two full thread turns protrude beyond the nut after tightening. A bolt that is too short—where the nut does not fully cover the thread—is a serious installation error that can lead to connection failure.
Product Grade Selection
Product Grade A: For threads M1.6 to M24 and nominal lengths ≤ 10d or 150mm, whichever is shorter
Product Grade B: For threads over M24 or lengths exceeding these limits
7. Standards Compliance
| Standard | Scope |
|---|---|
| DIN 933 | Hexagon head bolts—full thread (original German standard) |
| ISO 4017 | International standard—same as DIN 933 (DIN has been largely replaced) |
| ISO 898-1 | Mechanical properties of carbon and alloy steel bolts |
| EN 10204 3.1 | Material test certificate (available for critical applications) |
Note: The DIN 933 standard has been officially withdrawn in favor of ISO 4017, but the designation remains in widespread commercial use.
8. Quick Selection Guide
| Requirement | Recommendation |
|---|---|
| General industrial, cost-effective | Grade 8.8, black oxide or zinc plated |
| High-strength critical joint | Grade 10.9, black oxide (or zinc with documented baking) |
| Outdoor / corrosion-prone | A2-70 (304) or A4-80 (316) stainless steel |
| Marine / chemical processing | A4-80 (316 stainless) |
| Thin-flange / blind hole assemblies | DIN 933 full thread (any grade) |
| Shear-load applications | Consider DIN 931 (partial thread) instead |
Final Thoughts
The DIN 933 hexagon head bolt is a workhorse fastener that belongs in every engineer's specification toolkit. Its full-thread design, wide size range (M4–M64), and multiple grade options (8.8, 10.9, A2-70, A4-80) make it suitable for everything from general machinery to critical oil and gas infrastructure.
When selecting DIN 933 bolts, match the grade to the strength requirement, the finish to the environment, and the length to the assembly thickness. Pay attention to hydrogen embrittlement risks with plated high-strength grades, and always ensure proper thread engagement. Done right, the DIN 933 bolt delivers reliable, long-lasting performance across the entire spectrum of industrial applications.
