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FULLERKREG supplies GB/T 9074.13-1988 carbon steel class 8.8 SEMS screws with trivalent zinc (Zinc Cr3) plating — pre-assembled three-piece fastener assemblies combining a cross recessed hexagon bolt, a single coil spring lock washer, and a plain washer into one captive unit. The high-strength 8.8 grade combined with RoHS-compliant Zinc Cr3 coating makes these the go-to choice for automotive, machinery, and industrial assembly applications requiring both strength and environmental compliance.
GB/T 9074.13-1988 defines a three-piece pre-assembled fastener (SEMS) consisting of:
The three components are permanently captivated onto the bolt shank before thread rolling. After threading, the outer thread diameter exceeds the inner diameter of the plain washer, making the assembly permanently inseparable. This eliminates loose washers on the assembly line and dramatically reduces installation time and error.
Assembly formula: GB9074.13 = GB29.2 + GB9074.24 + GB9074.26
The washer stack order from bolt head outward is: Plain Washer → Spring Lock Washer → Bolt Head (the plain washer sits closest to the workpiece surface).
| Property | Specification |
|---|---|
| Material | Medium Carbon Steel (quenched & tempered) |
| Surface Finish | Zinc Cr3 (Trivalent Chromium Zinc Plating) |
| Plating Appearance | Silver-grey |
| Plating Thickness | Typically 5–8 µm |
| Salt Spray Resistance | ≥ 24 hours (white rust per ISO 9227) |
| Property Class | 8.8 |
| Tensile Strength | ≥ 800 MPa |
| Yield Strength (0.2% proof) | ≥ 640 MPa |
| Hardness | 22–32 HRC |
| RoHS / ELV Compliant | Yes — Cr3 (trivalent), no hexavalent chromium (Cr6+) |
| REACH Compliant | Yes |
| Property | Zinc Yellow (Cr6+) | Zinc Cr3 (Trivalent) |
|---|---|---|
| Chromate Type | Hexavalent Cr6+ | Trivalent Cr3+ |
| RoHS Compliant | No | Yes |
| EU ELV / REACH | Restricted | Compliant |
| Appearance | Yellow / iridescent | Silver-grey |
| Corrosion Resistance | Good | Good (≥ 72 h salt spray) |
| Automotive / Electronics Use | Phased out | Standard requirement |
Washer dimensions conform to GB9074.24 (plain washer) and GB9074.26 (spring lock washer). All dimensions in millimeters (mm).
| Thread Size | Inner Dia. d₁ (mm) | Outer Dia. d₂ (mm) | Thickness h (mm) |
|---|---|---|---|
| M4 | 4.3 | 9.0 | 0.8 |
| M5 | 5.3 | 10.0 | 1.0 |
| M6 | 6.4 | 12.0 | 1.6 |
| M8 | 8.4 | 16.0 | 1.6 |
| M10 | 10.5 | 20.0 | 2.0 |
| Thread Size | Inner Dia. d₁ (mm) | Outer Dia. d₂ (mm) | Thickness s (mm) | Width b (mm) |
|---|---|---|---|---|
| M4 | 4.1 | 7.1 | 0.9 | 1.5 |
| M5 | 5.1 | 8.7 | 1.2 | 1.8 |
| M6 | 6.1 | 10.2 | 1.6 | 2.0 |
| M8 | 8.1 | 13.0 | 2.0 | 2.5 |
| M10 | 10.2 | 16.2 | 2.5 | 3.0 |
All dimensions in millimeters (mm). Bolt head dimensions per GB29.2. Nominal lengths per standard series.
| Thread Size | Pitch (mm) | Head Width Across Flats s (mm) | Head Width Across Corners e (mm) | Head Height k (mm) | Cross Recess Depth (mm) | Min. Grip Length (mm) | Nominal Length Range L (mm) | Est. Unit Weight (g/pc) — @L16 |
|---|---|---|---|---|---|---|---|---|
| M4 | 0.7 | 7 | 7.66 | 2.8 | 1.8 | 10 | 10–40 | ≈ 1.5 |
| M5 | 0.8 | 8 | 8.79 | 3.5 | 2.1 | 12 | 10–50 | ≈ 2.8 |
| M6 | 1.0 | 10 | 11.05 | 4.0 | 2.4 | 14 | 12–60 | ≈ 4.8 |
| M8 | 1.25 | 13 | 14.38 | 5.3 | 3.0 | 18 | 16–80 | ≈ 10.5 |
| M10 | 1.5 | 16 | 17.77 | 6.4 | 3.6 | 22 | 20–100 | ≈ 19.0 |
Note: Unit weights are approximate reference values for L=16mm. Actual weight varies with nominal length. Contact FULLERKREG for precise weight data for your specific length requirement.
GB9074.13 carbon steel 8.8 Zinc Cr3 SEMS screws are widely specified in high-strength, RoHS-compliant assembly applications across automotive, machinery, and electronics industries:
Standard: GB/T 9074.13-1988 | Material: Carbon Steel | Finish: Zinc Cr3 (Trivalent Zinc) | Property Class: 8.8 | Brand: FULLERKREG
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