FULLERKREG DIN 6912 Low Head Socket Cap Screws — Grade 8.8 | 10B21 Steel | Zinc Plated Cr3
FULLERKREG DIN 6912 Grade 8.8 low head socket cap screws are high-strength metric fasteners combining a reduced-height hex socket head with a pilot recess (centre hole) in the socket. The pilot recess enables use of a ball-end hex key at angles up to 25°, making these screws ideal for confined spaces and recessed installations where straight-on access is impossible.
Manufactured from 10B21 boron-alloyed carbon steel and heat-treated to ISO 898-1 Grade 8.8, these screws deliver high tensile and proof load strength for demanding structural and mechanical assemblies. The zinc plating with Cr3 (trivalent chromium) passivation provides reliable corrosion protection while remaining fully RoHS compliant — free from hexavalent chromium (Cr6+).
Key Features
-
Standard: DIN 6912 — Hexagon socket head cap screws with low head and pilot recess
-
Material: 10B21 boron-alloyed carbon steel (medium-carbon, boron-treated for hardenability)
-
Property Class: Grade 8.8 (per ISO 898-1)
-
Surface Treatment: Zinc plated with Cr3 (trivalent chromium) passivation — RoHS compliant, Cr6+-free
-
Head Style: Low profile (reduced height) hex socket cap head — approximately 60% of standard DIN 912 head height
-
Drive: Internal hex (Allen / hex socket) with pilot recess (centre hole)
-
Pilot Recess Advantage: Allows ball-end hex key engagement at up to 25° angle — critical for blind or angled access
-
Thread: Metric coarse thread (ISO 68-1), right-hand
-
Size Range: M3 to M20
DIN 6912 vs. DIN 7984 vs. DIN 912: Key Differences
| Feature |
DIN 6912 (This Product) |
DIN 7984 |
DIN 912 (Standard Socket Cap) |
| Head Height |
Low (approx. 60% of DIN 912) |
Low (approx. 60% of DIN 912) |
Standard full height |
| Pilot Recess (Centre Hole) |
✅ Yes — centre hole in socket |
❌ No |
❌ No |
| Ball-End Hex Key Access |
✅ Up to 25° off-axis |
⚠️ Limited — ball-end slips without pilot |
⚠️ Limited — ball-end slips without pilot |
| Hex Key Size (e.g. M6) |
4 mm |
3 mm (smaller than DIN 6912) |
5 mm (full size) |
| Head Diameter dk (e.g. M6) |
10.0 mm |
10.0 mm |
10.0 mm |
| Head Height k (e.g. M6) |
3.3 mm |
3.0 mm |
6.0 mm |
| Socket Depth (e.g. M6) |
Deeper — accommodates pilot recess |
Shallower — no pilot recess |
Full depth standard socket |
| Torque Capacity |
Medium — larger hex key than DIN 7984 |
Lower — smaller hex key size |
Full torque capacity |
| Clearance Required |
Minimal — ideal for thin flanges |
Minimal — ideal for thin flanges |
Standard clearance needed |
| Governing Standard |
DIN 6912 / ISO 14580 |
DIN 7984 |
DIN 912 / ISO 4762 |
| Best For |
Low clearance + angled access required |
Low clearance, straight-on access only |
General-purpose, high-torque applications |
Material: 10B21 Boron-Alloyed Carbon Steel
10B21 is a medium-low carbon steel with boron addition (0.0005–0.003% B), widely used for high-strength fastener production. The boron addition significantly improves hardenability — allowing the steel to achieve Grade 8.8 mechanical properties through heat treatment with lower carbon content than conventional carbon steels, resulting in better cold-formability and consistent mechanical performance.
- Carbon content: ~0.18–0.23% (low-to-medium carbon)
- Boron addition: 0.0005–0.003% — enhances hardenability without increasing brittleness
- Manganese content: ~0.70–1.00% — contributes to strength and hardenability
- Excellent cold-heading formability — consistent head geometry and thread form
- Heat treated (quenched and tempered) to achieve Grade 8.8 mechanical properties
Mechanical Properties — Grade 8.8 (ISO 898-1)
| Property |
Value |
Standard Reference |
| Property Class |
8.8 |
ISO 898-1 |
| Material |
10B21 Boron-Alloyed Carbon Steel |
— |
| Tensile Strength (min.) |
800 MPa |
ISO 898-1 |
| Proof Load Stress |
600 MPa |
ISO 898-1 |
| 0.2% Yield Strength (min.) |
640 MPa |
ISO 898-1 |
| Elongation (min.) |
12% |
ISO 898-1 |
| Reduction of Area (min.) |
52% |
ISO 898-1 |
| Hardness (Vickers) |
245 – 335 HV |
ISO 898-1 |
| Hardness (Rockwell) |
22 – 34 HRC |
ISO 898-1 |
| Impact Strength |
Good — quenched & tempered microstructure |
— |
| Operating Temperature |
−50°C to +150°C (continuous) |
ISO 898-1 Note |
Surface Treatment: Zinc Plating with Cr3 Passivation
FULLERKREG DIN 6912 Grade 8.8 screws are finished with electrolytic zinc plating followed by trivalent chromium (Cr3) passivation:
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Zinc layer thickness: Typically 5–8 μm (per ISO 4042 / DIN 50979)
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Passivation: Cr3 (trivalent chromium) — blue-white or iridescent finish
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RoHS compliant: Cr3 passivation contains no hexavalent chromium (Cr6+) — fully compliant with EU RoHS Directive 2011/65/EU and ELV Directive
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Salt spray resistance: ≥ 72 hours to white corrosion, ≥ 120 hours to red rust (per ISO 9227)
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Hydrogen embrittlement: Post-plating baking (de-embrittlement) applied for Grade 8.8 per ISO 4042 to eliminate hydrogen embrittlement risk
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Appearance: Bright silver-blue finish; uniform coating
Dimensional Specifications (DIN 6912)
All dimensions per DIN 6912:2021. Thread per ISO 68-1 metric coarse.
| Size |
Thread Pitch (mm) |
Head Dia. dk (mm) |
Head Height k (mm) |
Hex Key Size s (mm) |
Pilot Recess Dia. (mm) |
Common Lengths (mm) |
| M3 |
0.5 |
5.5 |
1.65 |
2.0 |
1.0 |
5, 6, 8, 10, 12, 16, 20 |
| M4 |
0.7 |
7.0 |
2.2 |
2.5 |
1.5 |
6, 8, 10, 12, 16, 20, 25 |
| M5 |
0.8 |
8.5 |
2.75 |
3.0 |
2.0 |
8, 10, 12, 16, 20, 25, 30 |
| M6 |
1.0 |
10.0 |
3.3 |
4.0 |
2.0 |
10, 12, 16, 20, 25, 30, 35, 40 |
| M8 |
1.25 |
13.0 |
4.4 |
5.0 |
2.5 |
12, 16, 20, 25, 30, 35, 40, 50 |
| M10 |
1.5 |
16.0 |
5.5 |
6.0 |
3.0 |
16, 20, 25, 30, 35, 40, 50, 60 |
| M12 |
1.75 |
18.0 |
6.6 |
8.0 |
4.0 |
20, 25, 30, 35, 40, 50, 60, 70 |
| M14 |
2.0 |
21.0 |
7.7 |
10.0 |
4.0 |
25, 30, 35, 40, 50, 60, 70, 80 |
| M16 |
2.0 |
24.0 |
8.8 |
10.0 |
4.0 |
25, 30, 35, 40, 50, 60, 70, 80, 100 |
| M20 |
2.5 |
30.0 |
11.0 |
12.0 |
5.0 |
30, 35, 40, 50, 60, 70, 80, 100 |
All dimensions are nominal per DIN 6912:2021. Zinc plating adds approximately 5–8 μm per surface — account for this in tight-tolerance applications. Consult FULLERKREG product listings for exact available size/length combinations. Tolerances per ISO 4759-1.
The Pilot Recess: Why It Matters
The pilot recess (also called centre hole or pilot hole) is a small cylindrical bore at the centre of the hex socket. It serves two critical functions:
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Ball-end hex key engagement: The pilot recess guides and stabilises the ball end of a ball-point hex key, allowing reliable torque transmission at angles up to 25° off-axis. Without the pilot recess, ball-end keys tend to slip out of the socket under load.
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Alignment aid: The recess acts as a visual and tactile centre reference during assembly, reducing the risk of cam-out and socket damage.
This feature makes DIN 6912 the preferred choice over DIN 7984 for recessed bolt patterns, flanged joints, and any assembly where the fastener is not directly accessible from above.
Installation & Torque Guidelines
Recommended installation torque values for Grade 8.8 DIN 6912 screws (dry, unlubricated, μ = 0.12):
| Size |
Recommended Torque (N·m) |
Hex Key Size (mm) |
Notes |
| M3 |
0.9 – 1.1 |
2.0 |
Use T-handle or short-arm key; avoid over-torque |
| M4 |
2.2 – 2.7 |
2.5 |
— |
| M5 |
4.5 – 5.5 |
3.0 |
— |
| M6 |
7.5 – 9.0 |
4.0 |
— |
| M8 |
18 – 22 |
5.0 |
— |
| M10 |
36 – 43 |
6.0 |
— |
| M12 |
62 – 75 |
8.0 |
— |
| M14 |
100 – 120 |
10.0 |
— |
| M16 |
155 – 185 |
10.0 |
— |
| M20 |
300 – 360 |
12.0 |
— |
Torque values are indicative for dry conditions (μ = 0.12) with standard thread fit. Zinc-plated surfaces: reduce torque by approximately 10–15% vs. dry values, or use a torque factor appropriate for the lubricant/coating. For critical joints, use a calibrated torque wrench and refer to joint-specific engineering calculations. Do not exceed the maximum torque for the hex key size to avoid socket rounding.
Hydrogen Embrittlement Considerations
Grade 8.8 fasteners are susceptible to hydrogen embrittlement (HE) during electroplating if not properly treated. FULLERKREG applies post-plating baking (de-embrittlement heat treatment) per ISO 4042:
- Baking temperature: 190–220°C for a minimum of 4 hours within 4 hours of plating
- This drives out absorbed hydrogen from the steel lattice, restoring ductility
- Eliminates the risk of delayed fracture under sustained tensile load
-
Do not re-plate or re-heat Grade 8.8 fasteners without re-applying the de-embrittlement process
- For applications with sustained high tensile loads, specify de-embrittlement certification when ordering
Typical Applications
- Thin-flange and low-clearance assemblies in automotive, machinery, and structural applications
- Engine components, gearbox housings, and drivetrain assemblies requiring low-profile fastening
- Industrial machinery frames, conveyor systems, and production equipment
- Steel structures, brackets, and flanged joints where head clearance is limited
- Precision equipment and instrumentation requiring high clamping force in confined spaces
- Automotive body panels, chassis components, and interior trim assemblies
- General mechanical engineering where Grade 8.8 strength and low head profile are both required
- Any assembly requiring angled hex key access due to obstructions or recessed bolt patterns
Compliance & Standards
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DIN 6912:2021 — Hexagon socket head cap screws with low head and pilot recess
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ISO 898-1 — Mechanical properties of fasteners made of carbon steel and alloy steel — bolts, screws and studs
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ISO 4042 — Fasteners: Electroplated coatings (zinc plating, de-embrittlement)
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DIN 50979 — Electrodeposited coatings: Zinc and zinc alloy coatings on iron or steel with Cr3 passivation
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ISO 9227 — Corrosion tests in artificial atmospheres: Salt spray tests
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ISO 68-1 — Metric screw threads: General plan
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ISO 4759-1 — Tolerances for fasteners
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RoHS Directive 2011/65/EU — Cr3 passivation is Cr6+-free and fully compliant
-
ELV Directive 2000/53/EC — No restricted substances; suitable for automotive applications
Packaging & Supply
- Available in bulk bags, plastic boxes, and custom packaging for OEM and MRO supply
- Standard packaging quantities: 25 pcs, 50 pcs, 100 pcs, 500 pcs, 1000 pcs (size-dependent)
- Wholesale and B2B pricing available — contact FULLERKREG for volume quotations
- Full material certifications (mill certs, ISO 898-1 compliance, hardness test reports) available on request
- De-embrittlement certification available on request for critical applications
- Custom lengths and non-standard sizes available on request (MOQ applies)
- RoHS and REACH compliant documentation available
Why Choose FULLERKREG DIN 6912 Grade 8.8 Zinc Cr3?
- 10B21 boron steel — consistent Grade 8.8 mechanical properties with excellent cold-heading formability
- Manufactured to DIN 6912:2021 dimensional standards — not nominal equivalents
- Grade 8.8 properties verified per ISO 898-1 with full hardness and tensile traceability
- Cr3 zinc plating — RoHS compliant, Cr6+-free, ≥ 72 h white rust / ≥ 120 h red rust salt spray resistance
- Post-plating de-embrittlement baking applied — eliminates hydrogen embrittlement risk
- Pilot recess geometry precisely formed for reliable ball-end hex key engagement at up to 25°
- Full size range M3–M20 with broad length availability for versatile application coverage
- Competitive lead times for standard sizes; custom configurations on request
