Socket Head Cap Screws (DIN 912 / ISO 4762)
Designed for critical high-tensile applications, these Socket Head Cap Screws (SHCS) provide superior clamping force compared to standard hex bolts. The cylindrical head with an internal hexagonal drive allows for installation in confined spaces where external wrenching is impossible. Ideal for counterbored holes in heavy machinery, die fixtures, and precision assemblies, ensuring a flush, snag-free surface profile while maintaining structural integrity under dynamic loads.
- High Tensile Strength: Class 12.9 offers 1200 MPa min.
- Compact Assembly: Internal drive reduces counterbore diameter.
- Precision Drive: Hex key engagement prevents cam-out.
- Fatigue Resistance: Rolled threads increase fatigue life.
- Versatile Mounting: Suitable for limited clearance areas.
- Standard Compliance: Strict adherence to DIN/ISO tolerances.
Technical Specifications
Product Name
Socket Head Cap Screw (SHCS) / Allen Bolt
Common Standards
DIN 912, ISO 4762, ANSI B18.3
Material Grades
Alloy Steel: Class 8.8, 10.9, 12.9 (Standard)
Stainless Steel: A2-70 (304), A4-80 (316)
Nominal Diameter
M1.6 – M64 (Custom sizes available upon request)
Thread Type
Metric Coarse (M), Metric Fine (MF), UNC, UNF
Drive Type
Hex Socket (Allen)
Surface Finish
Black Oxide (Thermal/Chemical), Zinc Plated (Cr3+), Geomet, Dacromet
Head Style
Cylindrical Head (Knurled or Smooth options available)
Why Transition from Hex Bolts to SHCS? In modern mechanical design, space optimization and weight reduction are critical. Socket Head Cap Screws offer a distinct advantage over traditional Hex Head Bolts (DIN 931/933):
Solving the Space Constraint: The internal hex drive eliminates the need for side clearance required by external wrenches. This allows engineers to place fasteners closer to flanges or sidewalls, reducing the overall footprint of castings and machined parts.
Superior Clamping Force (Preload): Standard SHCS are manufactured to Class 12.9 (Alloy Steel), providing a tensile strength of 1200 MPa and a yield strength of 1080 MPa. This is significantly higher than the standard Class 8.8 hex bolt (800 MPa). This allows for fewer bolts to be used to achieve the same clamping force, reducing drilling operations and assembly time.
Safety & Aesthetics: When installed in a counterbored hole, the head sits flush with or below the surface. This eliminates potential catch points for clothing or moving parts, essential for rotating machinery and conveyor systems.
The following table represents standard metric dimensions for reference during design planning.
| Thread Size (d) | Pitch (P) | Head Diameter (dk) Max | Head Height (k) Max | Socket Width (s) | Key Engagement (t) Min |
| M3 | 0.5 mm | 5.50 mm | 3.00 mm | 2.5 mm | 1.3 mm |
| M4 | 0.7 mm | 7.00 mm | 4.00 mm | 3.0 mm | 2.0 mm |
| M5 | 0.8 mm | 8.50 mm | 5.00 mm | 4.0 mm | 2.5 mm |
| M6 | 1.0 mm | 10.00 mm | 6.00 mm | 5.0 mm | 3.0 mm |
| M8 | 1.25 mm | 13.00 mm | 8.00 mm | 6.0 mm | 4.0 mm |
| M10 | 1.5 mm | 16.00 mm | 10.00 mm | 8.0 mm | 5.0 mm |
| M12 | 1.75 mm | 18.00 mm | 12.00 mm | 10.0 mm | 6.0 mm |
| M16 | 2.0 mm | 24.00 mm | 16.00 mm | 14.0 mm | 8.0 mm |
Installation Best Practices for Reliability
Torque Control: To maximize the benefit of Class 12.9 fasteners, precise torque control is mandatory. Utilize a calibrated torque wrench. Over-tightening can yield the screw; under-tightening leads to fatigue failure under cyclic loading.
Lubrication & K-Factor: Be aware that the torque-tension relationship is heavily influenced by friction.
Black Oxide (Dry/Light Oil): K ≈ 0.20
Zinc Plated + Lubricant: K ≈ 0.12 – 0.15
Warning: Applying standard dry torque values to a lubricated screw can result in bolt yielding due to excessive preload.
Washer Selection: Standard flat washers (DIN 125) are often too wide for SHCS counterbores. Use DIN 433 (Small OD Washers) designed specifically for Socket Head Cap Screws to ensure proper seating without interference.
Hole Preparation: Ensure counterbores are concentric to the tapped hole. Misalignment causes bending stress under the head (fillet), which is a primary cause of fatigue fracture in high-cycle applications.
Related Products
FAQ
What is the difference between DIN 912 and ISO 4762?
DIN 912 and ISO 4762 are functionally interchangeable for most standard applications. They share the same geometric dimensions and mechanical property requirements. However, minor variations in the head knurling or the under-head fillet radius may exist depending on the manufacturer, but these rarely impact fitment in standard counterbores.
When should I use Class 12.9 vs. Stainless Steel A4-80?
Choose Class 12.9 Alloy Steel for maximum strength (1200 MPa) in non-corrosive environments or where high clamping force is the priority. Choose Stainless Steel A4-80 (800 MPa) for applications requiring corrosion resistance (e.g., marine, chemical processing) where the reduced tensile strength is acceptable for the design load.
Why do some Socket Head Cap Screws have knurled heads?
Knurling on the head (Standard DIN 912 feature) is designed to provide grip for finger tightening during the initial assembly phase before the tool is engaged. It does not affect the mechanical strength or torque capability of the screw.
How is the length of a Socket Head Cap Screw measured?
The length is measured from underneath the head to the end of the threads (bearing surface to tip). The head itself is not included in the length measurement. This contrasts with Flat Head (Countersunk) screws, where the length includes the head.
Can I use a standard hex nut with a Socket Head Cap Screw?
Yes, but ensure the material grade matches. If you are using a Class 12.9 SHCS, you must use a Class 12 High-Strength Nut (DIN 934 / ISO 4032) to prevent thread stripping in the nut. Using a standard Class 8 nut will result in the nut failing before the bolt reaches its full proof load capacity.