Home » DIN 7991 Flat Head Countersunk Socket Cap Screw A2 Stainless

DIN 7991 Flat Head Countersunk Socket Cap Screw A2 Stainless

FULLERKREG DIN 7991 / ISO 10642 A2 Stainless Steel Flat Head Countersunk Socket Cap Screws

FULLERKREG DIN 7991 / ISO 10642 A2 Stainless Steel Flat Head Countersunk Socket Cap Screws are corrosion-resistant fasteners featuring a 90° countersunk flat head with a hexagon socket drive. Manufactured from A2 (SUS304) austenitic stainless steel with a passivated natural finish, these screws are designed to sit flush with or below the surface of the mating material when installed in a countersunk hole. The flush-fit design eliminates protruding heads, providing a clean, snag-free surface finish ideal for aesthetic, safety-critical, and aerodynamic applications.

Product Specifications

  • Standards: DIN 7991 / ISO 10642
  • Material: A2 Stainless Steel (SUS304 / 18-8)
  • Strength Grade: A2-070
  • Tensile Strength: Min. 700 MPa
  • Proof Load Stress (Rp0.2): Min. 450 MPa
  • Hardness: ≤95 HRB (max. 210 HV)
  • Head Type: Flat countersunk head, 90° included angle
  • Surface Treatment: Passivation — natural silver finish (pickling & passivation)
  • Thread Type: Metric coarse, full thread
  • Thread Tolerance: 6g
  • Drive Type: Hexagon socket (Allen key / hex key)
  • Sizes Available: M3 – M20

Countersunk Head Design — What Makes DIN 7991 Different

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, aesthetic, safety, aerodynamic Low-profile aesthetic High-torque structural

Material — A2 Stainless Steel (SUS304) Chemical Composition (%)

All values are maximum unless a range is indicated.

Grade C (max) Si (max) Mn (max) P (max) S (max) Cr Ni
SUS304 (A2) ≤0.08 ≤1.00 ≤2.00 ≤0.045 ≤0.030 18.00–20.00 8.00–10.50

Mechanical Properties — A2-070 (ISO 3506-1)

“A2-070” is the property class designation per ISO 3506-1. “A2” refers to the austenitic stainless steel grade (SUS304), and “070” indicates a minimum tensile strength of 700 MPa.

Property Requirement Unit
Tensile Strength (Rm) Min. 700 MPa
Proof Load Stress (Rp0.2) Min. 450 MPa
Hardness (max) ≤95 HRB / ≤210 HV HRB / HV
Elongation after fracture (A) Min. 25 %
Thread Tolerance Class 6g —
Head Angle 90° degrees
Surface Treatment Passivation (natural finish) —

Key Features

  • Flush-fit countersunk head — 90° flat head sits flush with or below the mating surface, eliminating protrusions for a clean, snag-free finish
  • A2 Stainless Steel (SUS304) — excellent corrosion resistance in atmospheric, freshwater, food processing, and mild chemical environments
  • Passivated natural finish — clean silver appearance with enhanced oxide layer for superior rust resistance
  • Hexagon socket drive — high torque transmission in a compact, recessed head profile
  • DIN 7991 / ISO 10642 dual standard — internationally recognized specification
  • Non-magnetic — suitable for applications sensitive to magnetic interference
  • Hygienic & food-safe — smooth flush surface compliant for food processing and medical equipment
  • RoHS & REACH compliant — no restricted hazardous substances
  • ISO/TS16949 quality management — hardness test, tensile test, and PPAP report available on request

Countersunk Hole Requirements

DIN 7991 countersunk screws require a properly prepared countersunk hole for correct installation. Key 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 torque transfer
  • Material consideration: In soft materials (aluminum, plastic), the countersink may deform under high torque — consider using a washer or reducing torque

Corrosion Resistance Guide — A2 (SUS304)

Environment A2 (SUS304) Performance Recommendation
Indoor / dry environments Excellent ✅ Ideal
Outdoor / atmospheric exposure Very good ✅ Suitable
Food processing / pharmaceutical Excellent ✅ Ideal
Freshwater / mild humidity Very good ✅ Suitable
Mild chemical exposure Good ✅ Generally suitable
Saltwater / marine (direct) Limited ⚠️ Consider A4 (SUS316)
Strong acids / chlorides Poor ❌ Not recommended

Applications

FULLERKREG DIN 7991 A2 stainless steel countersunk socket cap screws are widely used wherever a flush or recessed fastener is required:

  • Furniture and cabinetry (flush surface finish)
  • Electronics enclosures and panels (snag-free, clean appearance)
  • Food processing and pharmaceutical machinery (hygienic flush surface)
  • Medical devices and laboratory instruments
  • Automotive interior trim and body panels
  • Architectural hardware and decorative fixtures
  • Aerospace and precision instruments (aerodynamic flush surface)
  • Hinges, brackets, and structural connections requiring flush fasteners
  • Any application where protruding screw heads are unacceptable

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: What does A2-070 mean?
A2-070 is the property class designation per ISO 3506-1 for stainless steel fasteners. “A2” refers to the austenitic stainless steel grade (SUS304), and “070” indicates a minimum tensile strength of 700 MPa. This is equivalent to the commonly used designation A2-70.

Q: Can DIN 7991 countersunk screws be used in soft materials like aluminum or plastic?
Yes, but with care. The wedge action of the countersunk head can cause deformation or cracking in soft materials under high torque. Use appropriate torque limits and consider a larger head diameter or a washer for very soft materials.

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 A2 stainless steel countersunk socket cap screws are manufactured under strict quality control procedures including:

  • Hardness test (≤95 HRB)
  • Tensile strength test (min. 700 MPa)
  • Head angle verification (90° countersink)
  • Dimensional inspection per DIN 7991 / ISO 10642
  • Chemical composition verification (SUS304)
  • Salt spray corrosion test
  • PPAP documentation available upon request

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

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