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FULLERKREG GB70-85 / ISO 4762 Grade 8.8 Socket Cap Screws with Zinc CR3 (trivalent chromate) plating are medium-strength hexagon socket head cap screws manufactured from 10B21 boron steel or 35# carbon steel. The electroplated zinc coating with CR3 trivalent chromate passivation provides reliable corrosion protection while meeting international environmental regulations. These screws conform to both the Chinese national standard GB 70-85 and the international ISO 4762 standard, making them suitable for domestic and global supply chains.
The zinc CR3 coating uses trivalent chromium (Cr3+) passivation, replacing the traditional hexavalent chromium (Cr6+) process. This is essential for compliance with international environmental regulations governing electronic, automotive, and consumer products:
| Regulation | Requirement | CR3 Zinc Compliance |
|---|---|---|
| EU RoHS Directive (2011/65/EU) | No hexavalent chromium (Cr6+) | ✅ Compliant |
| EU REACH Regulation | No SVHC restricted substances | ✅ Compliant |
| ELV Directive (2000/53/EC) | No Cr6+ in vehicle components | ✅ Compliant |
| China RoHS (GB/T 26572) | No restricted hazardous substances | ✅ Compliant |
FULLERKREG GB70-85 Grade 8.8 socket cap screws are manufactured from 10B21 boron-alloyed steel or 35# medium carbon steel. 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 |
| 35# Steel | 0.32–0.39 | 0.17–0.37 | 0.50–0.80 | ≤0.035 | ≤0.035 | — |
| Property | Requirement | Unit |
|---|---|---|
| Tensile Strength (Rm) | Min. 800 | MPa |
| Yield Strength / Proof Load Stress (Rp0.2) | Min. 640 | MPa |
| Core Hardness | 22–32 | HRC |
| Surface Hardness (max) | ≤36 | HRC |
| Elongation after fracture (A) | Min. 12 | % |
| Reduction of area (Z) | Min. 52 | % |
| Thread Tolerance Class | 6g | — |
| Surface Treatment | Zinc CR3 (trivalent chromate) | — |
GB 70-85 is the Chinese national standard for hexagon socket head cap screws issued in 1985. It is dimensionally compatible with ISO 4762 and DIN 912 for most common sizes, making these screws interchangeable in most applications.
| Aspect | GB 70-85 | ISO 4762 / DIN 912 |
|---|---|---|
| Issuing body | China National Standard (GB) | ISO / DIN (International / German) |
| Year | 1985 | ISO 4762: 2004 / DIN 912: 2014 |
| Head dimensions | Compatible for M3–M48 | Compatible for M3–M48 |
| Thread standard | GB/T 197 metric thread | ISO 261 metric thread |
| Mechanical requirements | GB/T 3098.1 | ISO 898-1 |
| Interchangeability | Generally interchangeable for standard sizes | |
FULLERKREG GB70-85 / ISO 4762 Grade 8.8 Zinc CR3 socket cap screws are widely used in:
| 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 | 5.50 | 5.32 | 3.00 | 2.86 | 2.5 | 1.3 | 3.00 | 2.86 |
| M4 | 0.7 | 7.00 | 6.78 | 4.00 | 3.82 | 3.0 | 2.0 | 4.00 | 3.82 |
| M5 | 0.8 | 8.50 | 8.28 | 5.00 | 4.82 | 4.0 | 2.5 | 5.00 | 4.82 |
| M6 | 1.0 | 10.00 | 9.78 | 6.00 | 5.70 | 5.0 | 3.0 | 6.00 | 5.82 |
| M8 | 1.25 | 13.00 | 12.73 | 8.00 | 7.64 | 6.0 | 4.0 | 8.00 | 7.78 |
| M10 | 1.5 | 16.00 | 15.73 | 10.00 | 9.64 | 8.0 | 5.0 | 10.00 | 9.78 |
| M12 | 1.75 | 18.00 | 17.73 | 12.00 | 11.57 | 10.0 | 6.0 | 12.00 | 11.73 |
| M14 | 2.0 | 21.00 | 20.67 | 14.00 | 13.57 | 12.0 | 7.0 | 14.00 | 13.73 |
| M16 | 2.0 | 24.00 | 23.67 | 16.00 | 15.57 | 14.0 | 8.0 | 16.00 | 15.73 |
| M20 | 2.5 | 30.00 | 29.67 | 20.00 | 19.48 | 17.0 | 10.0 | 20.00 | 19.67 |
| M24 | 3.0 | 36.00 | 35.61 | 24.00 | 23.48 | 19.0 | 12.0 | 24.00 | 23.67 |
| M30 | 3.5 | 45.00 | 44.61 | 30.00 | 29.48 | 22.0 | 15.5 | 30.00 | 29.67 |
| M36 | 4.0 | 54.00 | 53.54 | 36.00 | 35.38 | 27.0 | 19.0 | 36.00 | 35.61 |
| M42 | 4.5 | 63.00 | 62.54 | 42.00 | 41.38 | 32.0 | 24.0 | 42.00 | 41.61 |
| M48 | 5.0 | 72.00 | 71.54 | 48.00 | 47.38 | 36.0 | 28.0 | 48.00 | 47.61 |
Q: Is GB 70-85 the same as ISO 4762 / DIN 912?
GB 70-85 is the Chinese national standard issued in 1985 and is dimensionally compatible with ISO 4762 and DIN 912 for standard sizes M3–M48. The mechanical requirements follow GB/T 3098.1, which aligns closely with ISO 898-1. In most applications, GB 70-85 and ISO 4762 screws are interchangeable.
Q: What is the difference between Zinc CR3 and traditional yellow zinc (Cr6+)?
Traditional yellow zinc chromate uses hexavalent chromium (Cr6+), which is a restricted hazardous substance under EU RoHS and REACH regulations. Zinc CR3 uses trivalent chromium (Cr3+), which provides equivalent or better corrosion protection without any restricted substances. CR3 is the environmentally compliant replacement for Cr6+ chromate.
Q: What corrosion resistance does Zinc CR3 provide?
Zinc CR3 plating typically provides 72–120 hours of salt spray resistance (per ISO 9227) before red rust appears, depending on plating thickness. This is significantly better than black oxide and suitable for most indoor and sheltered outdoor applications.
Q: Can I get RoHS compliance documentation?
Yes. FULLERKREG provides RoHS compliance declarations, material certificates, and test reports upon request for all zinc CR3 plated products.
Q: What is the minimum order quantity?
We supply both small quantities and large bulk orders. Please contact our sales team for pricing and MOQ details.
All FULLERKREG GB70-85 / ISO 4762 Grade 8.8 Zinc CR3 socket cap screws are manufactured under strict quality control procedures including:
For wholesale pricing, bulk orders, RoHS documentation, or technical inquiries, please contact our sales team.
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