Home » DIN 7991 Flat Head Countersunk Socket Cap Screw Grade 10.9 Black

DIN 7991 Flat Head Countersunk Socket Cap Screw Grade 10.9 Black

FULLERKREG DIN 7991 / ISO 10642 Grade 10.9 Black Flat Head Countersunk Socket Cap Screws

FULLERKREG DIN 7991 / ISO 10642 Grade 10.9 Black Flat Head Countersunk Socket Cap Screws are high-strength fasteners featuring a 90° countersunk flat head with a hexagon socket drive. Manufactured from 10B21 boron-alloyed steel with a black oxide surface treatment, these screws deliver Grade 10.9 tensile strength (min. 1,040 MPa) in a flush-fit profile. When installed in a properly prepared 90° countersunk hole, the head sits flush with or below the mating surface, providing a clean, snag-free, professional black finish. They are the preferred choice for high-strength structural assemblies, robotics, automotive, and precision machinery where both maximum clamping force and a flush surface are required.

Product Specifications

  • Standards: DIN 7991 / ISO 10642
  • Strength Grade: 10.9 (heat treated)
  • Material: 10B21 boron-alloyed steel
  • Tensile Strength: Min. 1,040 MPa
  • Yield Strength: Min. 940 MPa
  • Hardness: HRC 32–39
  • Head Type: Flat countersunk head, 90° included angle
  • Surface Treatment: Black oxide (blackening)
  • Thread Type: Metric coarse, full thread
  • Thread Tolerance: 6g
  • Drive Type: Hexagon socket (Allen key / hex key)
  • Sizes Available: M3 – M20

Countersunk Head Design — DIN 7991 vs Other Head Types

The DIN 7991 countersunk socket cap screw is fundamentally different from button head and cylindrical head screws. Understanding the countersunk design helps you select the right fastener:

Property DIN 7991 Countersunk (This Page) ISO 7380-1 Button Head DIN 912 Socket Cap
Head profile 90° flat cone — flush with surface Low dome above surface Cylinder above surface
Installed appearance Completely flush / recessed Protrudes above surface Protrudes above surface
Countersunk hole required Yes — 90° countersink No No
Snag-free surface Yes — no protrusion Minimal protrusion Significant protrusion
Clamping load direction Axial + radial (cone wedge action) Axial only Axial only
Max. tightening torque Moderate (socket depth limited) Lower Highest
Best for Flush-fit, high-strength, structural Low-profile aesthetic High-torque structural

Grade 10.9 vs Stainless A2-070 — Strength Comparison

Property Grade 10.9 Black (This Page) A2-070 Stainless A4-070 Stainless
Material 10B21 boron steel SUS304 SUS316
Tensile strength Min. 1,040 MPa Min. 700 MPa Min. 700 MPa
Yield strength Min. 940 MPa Min. 450 MPa Min. 450 MPa
Hardness HRC 32–39 ≤95 HRB ≤95 HRB
Surface Black oxide Passivated Passivated
Corrosion resistance Moderate (indoor) Excellent Superior (marine)
Best for High-strength structural, robotics, automotive Food, medical, outdoor Marine, chemical

Material — 10B21 Boron Steel Chemical Composition (%)

FULLERKREG DIN 7991 Grade 10.9 black countersunk screws are manufactured from 10B21 boron-alloyed steel. The addition of boron (B) significantly improves hardenability, enabling Grade 10.9 mechanical properties with a leaner alloy composition. All values are maximum unless a range is indicated.

Grade C Si (max) Mn P (max) S (max) B
10B21 0.18–0.23 ≤0.30 0.80–1.10 ≤0.030 ≤0.030 0.0005–0.003

Mechanical Properties — Grade 10.9 (ISO 898-1)

Property Requirement Unit
Tensile Strength (Rm) Min. 1,040 MPa
Yield Strength / Proof Load Stress (Rp0.2) Min. 940 MPa
Core Hardness 32–39 HRC
Surface Hardness (max) ≤44 HRC
Elongation after fracture (A) Min. 9 %
Reduction of area (Z) Min. 48 %
Impact energy (KV) at room temp. Min. 37 J
Head Angle 90° degrees
Thread Tolerance Class 6g —
Surface Treatment Black oxide (blackening) —

Key Features

  • Flush-fit countersunk head — 90° flat head sits flush with or below the mating surface, eliminating protrusions for a clean, snag-free black finish
  • Grade 10.9 high strength — 1,040 MPa tensile strength, 49% stronger than A2-070 stainless (700 MPa), in a flush-fit profile
  • Black oxide finish — professional matte black appearance with minimal dimensional impact on thread fit and countersink seating
  • 10B21 boron steel — excellent hardenability and consistent mechanical properties through heat treatment
  • Hexagon socket drive — high torque transmission in a compact, recessed head profile
  • DIN 7991 / ISO 10642 dual standard — internationally recognized specification
  • ISO/TS16949 quality management — hardness test, tensile test, and PPAP report available on request

Applications

FULLERKREG DIN 7991 Grade 10.9 black countersunk socket cap screws are widely used in high-strength applications requiring a flush surface:

  • Robotics and automation equipment frames (high strength + flush surface)
  • Automotive structural components and chassis assemblies
  • Precision machinery and CNC equipment
  • Bicycle frames, motorcycle components, and sporting equipment
  • Electronics enclosures requiring high-strength flush fasteners
  • Hinges, brackets, and structural connections requiring flush fasteners
  • Industrial fixtures and tooling
  • Any application requiring Grade 10.9 strength with a flush countersunk profile

Countersunk Hole Requirements

  • Countersink angle: 90° included angle (standard metric countersink)
  • Countersink diameter: Must match or slightly exceed the screw head diameter (dk) to allow flush seating
  • Surface finish: Smooth countersink surface ensures consistent seating and accurate torque transfer
  • Material consideration: In soft materials (aluminum, plastic), the countersink may deform under high torque — reduce torque or use a larger head diameter
  • Note: Black oxide coating (1–2 μm) has negligible effect on countersink fit

Dimensional Specifications — DIN 7991 / ISO 10642 (Unit: mm)

Thread (d) Pitch (p) Head Dia. dk Max. Head Dia. dk Min. Head Height k Max. Head Height k Min. Key Size s Key Depth t Min. Body Dia. ds Max. Body Dia. ds Min.
M3 0.5 6.72 6.48 1.86 1.66 2.0 1.1 3.00 2.86
M4 0.7 8.96 8.62 2.48 2.18 2.5 1.5 4.00 3.82
M5 0.8 11.20 10.82 3.10 2.72 3.0 2.0 5.00 4.82
M6 1.0 13.44 13.02 3.72 3.32 4.0 2.5 6.00 5.82
M8 1.25 17.92 17.42 4.96 4.46 5.0 3.5 8.00 7.78
M10 1.5 22.40 21.82 6.20 5.52 6.0 4.4 10.00 9.78
M12 1.75 26.88 26.22 7.44 6.64 8.0 5.3 12.00 11.73
M16 2.0 33.60 32.82 8.80 7.90 10.0 6.8 16.00 15.73
M20 2.5 40.32 39.42 10.16 9.06 12.0 8.2 20.00 19.67

Frequently Asked Questions

Q: What is the difference between DIN 7991 and ISO 10642?
DIN 7991 is the German standard for flat head countersunk socket cap screws. ISO 10642 is the equivalent international standard. The two are dimensionally identical and fully interchangeable. FULLERKREG screws comply with both standards.

Q: What countersink angle is required for DIN 7991 screws?
DIN 7991 uses a 90° included angle countersink, which is the standard metric countersink angle. Ensure your countersink tool or pre-drilled hole uses a 90° angle for correct flush seating.

Q: Why choose Grade 10.9 instead of stainless steel for countersunk screws?
Grade 10.9 provides 1,040 MPa tensile strength — 49% higher than A2-070 stainless (700 MPa). For high-strength structural joints, robotics, and automotive applications where maximum clamping force is required and corrosion resistance is less critical, Grade 10.9 is the correct choice.

Q: Does the black oxide coating affect the countersink fit?
No. Black oxide coating is only 1–2 μm thick and has negligible effect on head dimensions or countersink seating. The screw will seat correctly in a standard 90° countersink.

Q: Can I get material certificates and test reports?
Yes. PPAP reports, material certificates, hardness test reports, and tensile test reports are available upon request for all FULLERKREG products.

Packaging & Availability

  • Standard sizes M3 – M20 available in stock
  • Bulk carton packaging; small box and custom packaging available
  • Material certificates and test reports available on request
  • PPAP report available on request
  • Custom lengths accepted for large orders

Download Specification

Quality Assurance

All FULLERKREG DIN 7991 Grade 10.9 black countersunk socket cap screws are manufactured under strict quality control procedures including:

  • Rockwell hardness test (HRC 32–39)
  • Tensile strength test (min. 1,040 MPa)
  • Head angle verification (90° countersink)
  • Dimensional inspection per DIN 7991 / ISO 10642
  • Chemical composition analysis (10B21, B content verified)
  • Salt spray corrosion test
  • PPAP documentation available upon request

For wholesale pricing, bulk orders, or technical inquiries, please contact our sales team.

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