DIN 7991 Hexagon Socket Countersunk Head Cap Screws Technical Datasheet
DIN 7991 Hexagon Socket Countersunk Head Cap Screws (Allen CSK Screws)
DIN 7991 Hexagon Socket Countersunk Head Cap Screws are high-strength machine screws designed for applications requiring a flush surface finish without sacrificing mechanical strength. The 90° countersunk head sits completely below the mounting surface when installed into a countersunk hole, making these screws ideal for machinery, precision equipment, automation systems, aerospace, automotive, and tooling applications.
Although DIN 7991 remains one of the most widely recognized fastener standards, it has been superseded by DIN EN ISO 10642. Both standards are commonly referenced in industry, and dimensional compatibility is generally maintained for most engineering applications.
Table of Contents
ITEM CODE: 1041
Standards
| Standard | Status |
|---|---|
| DIN 7991 | Original German Standard |
| DIN EN ISO 10642 | Current International Standard |
| ISO 10642 | International Equivalent |
Dimensions
| d1 | M2 | M2.5 | M3 | M4 | M5 | M6 | M8 | M10 | M12 | M16 | M20 | M24 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| d2 max | 4 | 5 | 6 | 8 | 10 | 12 | 16 | 20 | 24 | 30 | 36 | 39 |
| k max | 1.2 | 1.5 | 1.7 | 2.3 | 2.8 | 3.3 | 4.4 | 5.5 | 6.5 | 7.5 | 8.5 | 14 |
| s | 1.3 | 1.5 | 2 | 2.5 | 3 | 4 | 5 | 6 | 8 | 10 | 12 | 14 |
| t | 0.75 | 0.8 | 1.2 | 1.8 | 2.3 | 2.5 | 3.5 | 4.4 | 4.6 | 5.3 | 5.9 | 10.3 |
| α | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 60° |
all dimensions in mm
Dimensions Tolerances:
General dimensional tolerances for standard metric fasteners—including thread diameter, overall length, head diameter, head height/thickness, across flats, and washer dimensions—are available in our Standard Dimensional Tolerances for Common Metric Fasteners guide.
Certain product-specific features, such as drive recess dimensions, socket depth, countersink geometry, under-head radii, and other special characteristics, are governed by the applicable DIN or ISO product standard and may not included in this datasheet.
Download Technical Datasheets
Stainless Steel
| Grade | Download |
|---|---|
| A2-70 (SS304) | ⬇️ Download Datasheet |
| A4-70 (SS316) | ⬇️ Download Datasheet |
Carbon Steel
| Property Class | Download |
|---|---|
| 10.9 | ⬇️ Download Datasheet |
| 12.9 | ⬇️ Download Datasheet |
Others
| Material | Download |
|---|---|
| Titanium G2 | ⬇️ Download Datasheet |
Mechanical Properties
| Material / Property Class | Tensile Strength | Yield Strength | Standard |
|---|---|---|---|
| Steel 8.8 | ≥ 800 MPa | ≥ 640 MPa | ISO 898-1 |
| Steel 10.9 | ≥ 1,040 MPa | ≥ 940 MPa | ISO 898-1 |
| Steel 12.9 | ≥ 1,220 MPa | ≥ 1,100 MPa | ISO 898-1 |
| Stainless Steel A2-70 | ≥ 700 MPa | ≥ 450 MPa | ISO 3506-1 |
| Stainless Steel A4-70 | ≥ 700 MPa | ≥ 450 MPa | ISO 3506-1 |
| Stainless Steel A4-80 | ≥ 800 MPa | ≥ 600 MPa | ISO 3506-1 |
| Titanium Grade 2 | Approx. 345 MPa | Approx. 275 MPa | ASTM B348 |
| Titanium Grade 5 | Approx. 895 MPa | Approx. 828 MPa | ASTM B348 |
Material Characteristics and Recommended Applications
| Material | Characteristics | Typical Applications |
|---|---|---|
| SS304 (A2-70) | Corrosion resistant, general-purpose | Machinery, Electronics, Food Equipment |
| SS316 (A4-70) | Superior corrosion resistance | Marine, Chemical, Offshore |
| Steel Class 8.8 | Medium tensile strength | Industrial machinery |
| Alloy Steel 10.9 | High tensile strength | Automotive, Heavy Equipment |
| Alloy Steel 12.9 | Very high tensile strength | Tooling, High-load assemblies |
| Titanium Grade 2 | Lightweight, corrosion resistant | Marine, Medical |
| Titanium Grade 5 | High strength-to-weight ratio | Aerospace, Racing, Defence |
Technical Specifications
| Property | Specification |
|---|---|
| Product Type | Hexagon Socket Countersunk Head Cap Screw |
| Standard | DIN 7991 / ISO 10642 |
| Drive Type | Internal Hex Socket |
| Head Angle | 90° |
| Thread | ISO Metric |
| Thread Direction | Right Hand |
| Thread Type | Fully Threaded |
| Strength Classes | A2-70, A4-70, A4-80, 8.8, 10.9, 12.9 |
| Diameter Range | M3–M24 (standard) |
| Finish Options | Plain, Black Oxide, Zinc Plated, Hot Dip Galvanized*, Geomet®, Dacromet®, PTFE, Passivated (*limited by size/application) |
| Manufacturing Process | Cold Forged / Precision Machined |
| RoHS Compliant | Available |
| REACH Compliant | Available |
DIN 7991 Socket CSK Head Screw Weight Chart
Weight in kgs. per 1,000 pcs. All weights are approximations.
| Diameter/ Length | M3 | M4 | M5 | M6 | M8 | M10 | M12 | M16 | M20 | M24 |
|---|---|---|---|---|---|---|---|---|---|---|
| 8 | 0.47 | 0.92 | 1.6 | 2.35 | ||||||
| 10 | 0.56 | 1.07 | 1.85 | 2.7 | 5.47 | |||||
| 12 | 0.65 | 1.23 | 2.1 | 3.05 | 6.1 | 10.1 | ||||
| 16 | 0.83 | 1.53 | 2.59 | 3.76 | 7.35 | 12.1 | ||||
| 20 | 1 | 1.84 | 3.09 | 4.46 | 8.6 | 14.1 | 21.2 | |||
| 25 | 1.35 | 2.23 | 3.71 | 5.34 | 10.2 | 16.6 | 24.8 | |||
| 30 | 1.63 | 2.9 | 4.33 | 6.22 | 11.7 | 19.1 | 28.5 | 51.8 | ||
| 35 | 3.4 | 5.43 | 7.1 | 13.3 | 21.6 | 32.1 | 58.4 | 91.4 | ||
| 40 | 3.9 | 6.2 | 8.83 | 14.8 | 24.1 | 35.7 | 65.1 | 102 | ||
| 50 | 7.74 | 11 | 19.9 | 30.1 | 43 | 78.4 | 123 | 179 | ||
| 60 | 24.8 | 35.7 | 54 | 91.7 | 143 | 209 | ||||
| 70 | 41.2 | 62.9 | 111 | 164 | 239 | |||||
| 80 | 127 | 200 | 269 | |||||||
| 90 | 143 | 226 | 299 | |||||||
| 100 | 253 | 340 |
Applications
DIN 7991 Socket CSK Screws are commonly used in:
- Machine tools
- Industrial machinery
- Precision equipment
- Automation systems
- Robotics
- Aerospace assemblies
- Automotive components
- Medical equipment
- Electronics enclosures
- Furniture hardware
- Defence equipment
- Renewable energy systems
- Railway equipment
- Tooling fixtures
Advantages
- Flush installation for smooth finished surfaces
- High-strength internal hex drive reduces cam-out
- Suitable for precision engineering applications
- Excellent appearance after installation
- High torque transmission compared to cross recess screws
- Available in corrosion-resistant materials
- Suitable for automation and robotic assembly
- Compatible with standard metric threaded components
- Wide availability across industrial sizes
- Suitable for high-load mechanical joints
Frequently Asked Questions
What is DIN 7991?
DIN 7991 specifies hexagon socket countersunk head cap screws with metric threads, designed to provide a flush surface after installation.
Is DIN 7991 still current?
DIN 7991 has been superseded by DIN EN ISO 10642, although DIN 7991 is still widely used as a commercial reference.
What is the difference between DIN 7991 and DIN 965?
DIN 7991 uses an internal hex (Allen) drive, allowing higher tightening torque and improved durability. DIN 965 uses a Phillips recess, making it more suitable for light- to medium-duty applications.
Why use a countersunk screw?
Countersunk screws provide a flush surface that improves appearance, reduces snagging, and is ideal where moving components or tight clearances are involved.
What tools are required?
DIN 7991 screws are tightened using standard metric hex keys or Allen bits.
Are DIN 7991 screws fully threaded?
Yes. Standard DIN 7991 screws are manufactured with full metric threads.
What strength classes are available?
Typical strength grades include:
A2-70
A4-70
A4-80
8.8
10.9
12.9
Can DIN 7991 screws be used outdoors?
Yes. Stainless steel A2 and especially A4 grades offer excellent corrosion resistance for outdoor and marine environments.
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