What are GB9074.17 Hex Head SEMS Screws?
GB9074.17 Hex Head SEMS Screws are pre-assembled combination fasteners consisting of three permanently integrated components: a hexagon head bolt (per GB5783), a flat washer (per GB9074.24), and a spring lock washer (per GB9074.26). The washers are captured onto the screw shank during the manufacturing process and cannot be separated during handling or installation — eliminating the need for manual washer placement on the assembly line.
The standard composition is: GB9074.17 = GB5783 (Hex Bolt) + GB9074.24 (Flat Washer) + GB9074.26 (Spring Washer)
This carbon steel variant is manufactured from 35K medium carbon steel, heat-treated to achieve Class 8.8 mechanical properties, and finished with a trivalent zinc (Zinc Cr3) electroplated coating. It delivers high tensile strength, reliable anti-loosening performance, and RoHS-compliant corrosion protection — making it the standard choice for high-volume industrial and automotive assembly applications.
Benefits of Using GB9074.17 Hex Head SEMS Screws
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Captive Washer Design: Flat washer and spring washer are permanently retained on the shank — no loose parts, no dropped washers during assembly or handling.
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High Strength — Class 8.8: 35K carbon steel heat-treated to 800 MPa minimum tensile strength, suitable for structural and load-bearing applications requiring reliable clamping force.
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RoHS-Compliant Zinc Cr3 Finish: Trivalent chromium zinc plating (Cr3) replaces hexavalent Cr6 — meets RoHS, ELV, and WEEE directives. Provides effective corrosion protection in standard indoor and light outdoor environments.
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Faster Assembly: Eliminates individual washer pick-and-place steps, significantly reducing assembly cycle time in production lines and maintenance operations.
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Reduced Error Rate: Prevents missing washers or incorrect washer stacking — critical in automated, high-speed assembly environments.
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Consistent Anti-Loosening: The spring washer delivers reliable vibration resistance; the flat washer distributes clamping load evenly across the bearing surface.
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Simplified Inventory: One SKU replaces three separate fastener components, streamlining procurement and reducing storage complexity.
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Cost-Effective: Carbon steel with zinc plating offers the best strength-to-cost ratio for high-volume applications where stainless steel is not required.
Material & Finish
| Component |
Material |
Grade / Standard |
Surface Finish |
| Hex Bolt (GB5783) |
Carbon Steel 35K |
Class 8.8 |
Zinc Plated Cr3 (Trivalent) |
| Flat Washer (GB9074.24) |
Carbon Steel |
— |
Zinc Plated Cr3 (Trivalent) |
| Spring Washer (GB9074.26) |
Carbon Steel 65Mn |
— |
Zinc Plated Cr3 (Trivalent) |
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Bolt Material: Carbon Steel 35K (medium carbon, quenched & tempered)
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Strength Class: Class 8.8 — Minimum tensile strength 800 MPa, proof load stress 640 MPa
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Surface Treatment: Zinc electroplating with trivalent chromium passivation (Zinc Cr3)
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Coating Thickness: Typically 5–8 µm zinc layer
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Salt Spray Resistance: ≥ 72 hours (white rust) per ISO 9227
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RoHS Compliant: Yes — Cr3 trivalent process, no hexavalent chromium (Cr6)
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Hydrogen Embrittlement Relief: De-embrittlement baking applied post-plating for Class 8.8 per GB/T 5267
Dimensions of Pre-Assembled Washers in GB9074.17 Hex Head SEMS Screws
The flat washer dimensions in GB9074.17 SEMS screws conform to GB9074.24. The spring washer conforms to GB9074.26. All dimensions in millimeters (mm).
Flat Washer Dimensions (GB9074.24)
| Thread Size |
Inner Diameter d₁ (mm) |
Outer Diameter d₂ (mm) |
Thickness h (mm) |
| M3 |
3.2 |
7.0 |
0.5 |
| 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 |
| M12 |
13.0 |
24.0 |
2.5 |
| M16 |
17.0 |
30.0 |
3.0 |
| M20 |
21.0 |
37.0 |
3.0 |
Spring Washer Dimensions (GB9074.26)
| Thread Size |
Inner Diameter d₁ (mm) |
Outer Diameter d₂ (mm) |
Thickness s (mm) |
Width b (mm) |
| M3 |
3.1 |
5.1 |
0.8 |
1.0 |
| M4 |
4.1 |
6.9 |
1.0 |
1.4 |
| M5 |
5.1 |
8.7 |
1.2 |
1.7 |
| M6 |
6.1 |
10.5 |
1.6 |
2.2 |
| M8 |
8.1 |
13.5 |
2.0 |
2.7 |
| M10 |
10.2 |
16.5 |
2.5 |
3.2 |
| M12 |
12.2 |
19.5 |
3.0 |
3.7 |
| M16 |
16.2 |
25.5 |
4.0 |
4.7 |
| M20 |
20.2 |
31.5 |
5.0 |
5.7 |
Dimensional Data — GB9074.17 Hex Head SEMS Screws
All dimensions in millimeters (mm). Bolt dimensions per GB5783. Nominal lengths (l) range from 6 mm to 200 mm depending on thread size.
| Thread Size |
Pitch P (mm) |
Head Width Across Flats s (mm) |
Head Width Across Corners e (mm) |
Head Height k (mm) |
Shank Diameter d₂ (mm) |
Min. Thread Length b (mm) l≤125 |
Min. Thread Length b (mm) l>125 |
Est. Unit Weight (g/pc) — M×20mm ref. |
| M3 |
0.5 |
5.5 |
6.01 |
2.0 |
2.86 |
12 |
— |
0.6 |
| M4 |
0.7 |
7.0 |
7.66 |
2.8 |
3.82 |
14 |
— |
1.3 |
| M5 |
0.8 |
8.0 |
8.79 |
3.5 |
4.82 |
16 |
— |
2.3 |
| M6 |
1.0 |
10.0 |
11.05 |
4.0 |
5.82 |
18 |
24 |
4.0 |
| M8 |
1.25 |
13.0 |
14.38 |
5.3 |
7.78 |
22 |
28 |
9.0 |
| M10 |
1.5 |
16.0 |
17.77 |
6.4 |
9.78 |
26 |
32 |
17.0 |
| M12 |
1.75 |
18.0 |
20.03 |
7.5 |
11.73 |
30 |
36 |
28.0 |
| M16 |
2.0 |
24.0 |
26.75 |
10.0 |
15.73 |
38 |
44 |
72.0 |
| M20 |
2.5 |
30.0 |
33.53 |
12.5 |
19.67 |
46 |
52 |
145.0 |
Note: Unit weights are reference values for carbon steel at the indicated nominal length. Carbon steel density ~7.85 g/cm³. Actual weights vary by length. Contact FULLERKREG for weight data at specific lengths.
Product Showcase
Applications
GB9074.17 Hex Head SEMS Screws in Class 8.8 carbon steel with Zinc Cr3 finish are the standard choice for high-volume industrial assembly where high strength and cost efficiency are the primary requirements:
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Automotive Manufacturing: Body panels, chassis brackets, engine bay components, interior trim — high-speed assembly lines benefit from the captive washer design and Class 8.8 clamping strength.
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Electronics & Electrical Enclosures: Sheet metal cabinets, control panels, switchgear — captive washers prevent contamination from loose hardware in sensitive environments.
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Industrial Machinery & Equipment: Guards, covers, access panels, structural frames — Class 8.8 provides reliable clamping in dynamic, vibration-prone environments.
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HVAC & Ventilation Systems: Duct flanges, fan housings, air handling units — zinc Cr3 coating provides adequate corrosion protection in standard indoor environments.
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Agricultural Equipment: Implements, frames, housings — high strength and cost efficiency suit the demanding requirements of agricultural machinery.
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Construction & Steel Structures: Secondary steel connections, brackets, fixings — Class 8.8 meets structural fastening requirements for non-critical connections.
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Appliance Manufacturing: White goods, HVAC units, commercial kitchen equipment — high-volume assembly with consistent torque and clamping performance.
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General Industrial MRO: Maintenance, repair, and overhaul applications across manufacturing, utilities, and infrastructure sectors.
Why FULLERKREG?
- 🏭 Direct Manufacturer: In-house production with full dimensional and mechanical traceability to GB9074.17-1988 and GB/T 3098.1 (Class 8.8).
- 📦 Wholesale & Bulk Supply: Competitive pricing for OEM, Tier-1 automotive, MRO, and distribution customers with flexible MOQ.
- 🔬 Quality Assurance: Mechanical property testing (tensile, hardness, proof load); salt spray testing per ISO 9227; material certificates available on request.
- 🌎 Global Export: Experienced in international shipping, export documentation, and RoHS/REACH compliance requirements.
- ⚡ Fast Lead Times: Large stock of standard sizes; custom lengths, thread specifications, and packaging available.
- 🤝 Technical Support: Engineering team available to assist with material selection (carbon steel vs stainless), torque specifications, coating options, and application guidance.
