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 on 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 A4 marine-grade variant is manufactured from SUS316 stainless steel, offering superior resistance to chloride corrosion, salt spray, and aggressive chemical environments compared to standard A2 grades. It is the preferred choice for marine, offshore, coastal, and chemical processing applications where long-term corrosion resistance is critical.
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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Superior Marine Corrosion Resistance: A4 (SUS316) contains molybdenum (Mo 2–3%), providing significantly better resistance to chloride pitting and crevice corrosion than A2 — essential for saltwater and coastal environments.
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Faster Assembly: Eliminates individual washer pick-and-place steps, reducing assembly cycle time in production and maintenance operations.
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Reduced Error Rate: Prevents missing washers or incorrect washer stacking — critical in automated, high-speed, or remote assembly environments.
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Consistent Clamping & 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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Compliance Ready: Manufactured to GB9074.17-1988 national standard with full dimensional and material traceability.
Material & Finish
| Component |
Material |
Grade / Standard |
Surface Finish |
| Hex Bolt (GB5783) |
Marine Stainless Steel A4 (SUS316) |
A4-70 |
Passivated / Whitened |
| Flat Washer (GB9074.24) |
Marine Stainless Steel A4 (SUS316) |
A4 |
Passivated / Whitened |
| Spring Washer (GB9074.26) |
Marine Stainless Steel A4 (SUS316) |
A4 |
Passivated / Whitened |
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Material: A4 Marine Stainless Steel (SUS316 / 1.4401) — contains 2–3% molybdenum for enhanced chloride resistance
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Strength Class: A4-70
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Surface: Passivated & Whitened (natural stainless appearance, enhanced corrosion resistance)
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RoHS Compliant: Yes
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Key Advantage vs A2: Molybdenum content provides superior resistance to pitting corrosion in chloride-rich environments (seawater, de-icing salts, chemical processing)
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 |
— |
0.5 |
| M4 |
0.7 |
7.0 |
7.66 |
2.8 |
3.82 |
14 |
— |
1.1 |
| M5 |
0.8 |
8.0 |
8.79 |
3.5 |
4.82 |
16 |
— |
2.0 |
| M6 |
1.0 |
10.0 |
11.05 |
4.0 |
5.82 |
18 |
24 |
3.5 |
| M8 |
1.25 |
13.0 |
14.38 |
5.3 |
7.78 |
22 |
28 |
8.0 |
| M10 |
1.5 |
16.0 |
17.77 |
6.4 |
9.78 |
26 |
32 |
15.0 |
| M12 |
1.75 |
18.0 |
20.03 |
7.5 |
11.73 |
30 |
36 |
25.0 |
| M16 |
2.0 |
24.0 |
26.75 |
10.0 |
15.73 |
38 |
44 |
65.0 |
| M20 |
2.5 |
30.0 |
33.53 |
12.5 |
19.67 |
46 |
52 |
130.0 |
Note: Unit weights are reference values for A4 stainless steel at the indicated nominal length. Actual weights vary by length. Contact FULLERKREG for weight data at specific lengths.
Product Showcase
Applications
GB9074.17 Hex Head SEMS Screws in A4 marine stainless steel are the preferred choice for environments where standard stainless steel is insufficient:
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Marine & Offshore Structures: Boat fittings, deck hardware, dock equipment, offshore platforms — direct saltwater exposure demands A4-grade molybdenum-bearing steel.
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Coastal & Waterfront Construction: Railings, walkways, structural brackets in salt-air environments where A2 would suffer accelerated pitting corrosion.
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Chemical Processing Equipment: Reactors, pipework flanges, pump housings — resistance to chlorides, acids, and process chemicals.
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Food & Beverage Processing: Hygienic equipment, washdown areas, CIP (clean-in-place) systems — A4 meets stricter hygiene and chemical resistance requirements.
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Pharmaceutical & Biotech Facilities: Cleanroom equipment, process vessels — corrosion resistance and surface integrity are critical.
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Swimming Pools & Water Treatment: Pool surrounds, filtration equipment, water treatment plants — chlorinated water environments require A4 grade.
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Desalination Plants: High-chloride brine environments where only molybdenum-bearing alloys provide adequate service life.
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Renewable Energy (Offshore): Offshore wind turbine structures, tidal energy equipment — permanent exposure to seawater spray.
Why FULLERKREG?
- 🏭 Direct Manufacturer: In-house production with full dimensional and material traceability to GB9074.17-1988.
- 📦 Wholesale & Bulk Supply: Competitive pricing for OEM, MRO, and distribution customers with flexible MOQ.
- 🔬 Quality Assurance: 100% dimensional inspection; material certificates (Mill Test Reports) and SUS316 material confirmation available on request.
- 🌎 Global Export: Experienced in international shipping, export documentation, and compliance requirements.
- ⚡ Fast Lead Times: Large stock of standard sizes in A4; custom lengths and packaging available.
- 🤝 Technical Support: Engineering team available to assist with grade selection (A2 vs A4), torque specifications, and application guidance.
