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FULLERKREG ISO7380 Button Head SEMS Screws in Alloy Steel (10B21) are a high-strength three-in-one captive fastener assembly: an ISO7380 low-profile button head screw with a pre-assembled flat washer (GB/T 9074.24) and spring washer (GB/T 9074.26) — delivering high clamping force, broad load distribution, vibration resistance, and faster assembly in a single black oxide finished alloy steel unit.
SEMS (pre-Subassembled and Edge-retained Metal Screws) are fasteners with one or more washers permanently captured on the shank before threading. The ISO7380 Button Head SEMS Screw is a tri-combination assembly consisting of three components:
| Component | Standard | Function |
|---|---|---|
| ① ISO7380 Button Head Cap Screw | ISO 7380 / ISO 7380.3 | Low-profile domed head with internal hex (Allen) drive; provides high clamping force at Class 10.9 strength |
| ② Flat Washer | GB/T 9074.24 | Distributes clamping load over a larger bearing area; protects substrate surface from indentation |
| ③ Spring Washer (Split Lock Washer) | GB/T 9074.26 | Provides elastic preload that resists self-loosening under vibration and dynamic loads |
All three components are permanently captured on the screw shank — the washers rotate freely but cannot be removed. Assembly order from head to workpiece: Screw Head → Spring Washer (GB9074.26) → Flat Washer (GB9074.24) → Thread end contacts workpiece.
Standard: ISO 7380.3 | Drive Type: Hexagon Socket (Allen Key) | Assembly: Tri-combination (Screw + Flat Washer + Spring Washer)
| Benefit | Details |
|---|---|
| 💪 High Strength | Class 10.9 alloy steel (10B21) delivers tensile strength ≥ 1040 MPa — significantly stronger than stainless steel grades, ideal for heavy-duty structural joints |
| ⚡ Faster Assembly | All three components pre-assembled — eliminates separate washer handling; reduces assembly time significantly in high-volume production |
| 🔒 No Lost Parts | Both flat and spring washers are captive on the shank — no dropped or missing washers on the production line |
| 🎯 Broad Load Distribution | Flat washer (GB9074.24) spreads clamping force over a larger bearing area, preventing pull-through on thin or soft substrates |
| 🔩 Vibration Resistance | Spring washer (GB9074.26) provides elastic preload that resists self-loosening under dynamic loads and vibration |
| ✨ Clean Aesthetics | Black oxide finish gives a uniform matte black appearance — ideal for visible surfaces in industrial, automotive, and consumer electronics applications |
| 🛡️ Black Oxide Finish | Provides mild corrosion resistance and reduces light reflection; typically used with supplementary oil or wax coating for enhanced protection |
| 📦 Simplified Inventory | One SKU replaces three separate components (screw + flat washer + spring washer), reducing procurement and storage complexity |
| ✅ Consistent Quality | Factory-assembled under controlled conditions ensures correct washer stack order and orientation every time |
| Property | Specification |
|---|---|
| Material | Alloy Steel 10B21 — screw, flat washer, and spring washer all in alloy steel |
| Surface Treatment | Black Oxide (Blackening) |
| Strength Grade | Class 10.9 |
| Tensile Strength | ≥ 1040 MPa |
| Proof Load Stress | ≥ 940 MPa |
| Yield Strength | ≥ 940 MPa (0.2% proof load) |
| Hardness | 32–39 HRC |
| Corrosion Resistance | Mild — black oxide provides basic protection; recommend supplementary oil or wax for outdoor or humid environments |
| Magnetic | Yes (ferromagnetic alloy steel) |
| RoHS Compliant | Yes |
Both washers are permanently captured on the screw shank. Assembly order from screw head: Spring Washer (GB9074.26) → Flat Washer (GB9074.24). The flat washer contacts the workpiece surface.
| Screw Size | Inner Dia. d₁ (mm) | Outer Dia. 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 |
| Screw Size | Inner Dia. d₁ (mm) | Outer Dia. d₂ (mm) | Thickness / Height s (mm) | Width b (mm) |
|---|---|---|---|---|
| M3 | 3.1 | 5.1 | 0.8 | 1.0 |
| M4 | 4.1 | 6.8 | 1.0 | 1.2 |
| M5 | 5.1 | 8.2 | 1.2 | 1.5 |
| M6 | 6.1 | 9.9 | 1.6 | 2.0 |
| M8 | 8.1 | 13.0 | 2.0 | 2.5 |
| M10 | 10.2 | 16.2 | 2.5 | 3.0 |
Note: Spring washer dimensions per GB/T 9074.26 (equivalent to GB/T 93). Inner diameter d₁ allows free rotation on screw shank. Both washers are captive and non-removable after assembly.
All dimensions in millimeters (mm). Tolerances per ISO 7380 and ISO 4759-1.
| Size | Pitch P (mm) | Head Dia. dk (mm) | Head Height k (mm) | Socket Size s (mm) | Socket Depth t (mm) | Min. Thread Length b (mm) | Approx. Unit Weight (g/pc) L=20mm |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 5.7 | 1.65 | 2 | 1.04 | 12 | 0.58 |
| M4 | 0.7 | 7.6 | 2.20 | 2.5 | 1.30 | 14 | 1.20 |
| M5 | 0.8 | 9.5 | 2.75 | 3 | 1.56 | 16 | 2.20 |
| M6 | 1.0 | 10.5 | 3.30 | 4 | 2.08 | 18 | 3.75 |
| M8 | 1.25 | 14.0 | 4.40 | 5 | 2.60 | 22 | 8.10 |
| M10 | 1.5 | 17.5 | 5.50 | 6 | 3.12 | 26 | 15.80 |
* Unit weight is approximate for L=20mm in alloy steel, including both pre-assembled washers (flat + spring). Actual weight varies with length. Contact FULLERKREG for weight data on specific lengths.
| Size | Available Lengths L (mm) |
|---|---|
| M3 | 6, 8, 10, 12, 16, 20, 25, 30 |
| M4 | 6, 8, 10, 12, 16, 20, 25, 30, 35, 40 |
| M5 | 8, 10, 12, 16, 20, 25, 30, 35, 40, 50 |
| M6 | 10, 12, 16, 20, 25, 30, 35, 40, 50, 60 |
| M8 | 12, 16, 20, 25, 30, 35, 40, 50, 60, 70, 80 |
| M10 | 16, 20, 25, 30, 35, 40, 50, 60, 70, 80 |
ISO7380 Button Head SEMS Screws in Alloy Steel Class 10.9 Black are ideal for high-strength structural joints where a low-profile head, captive dual-washer stack, vibration resistance, and a clean black finish are required simultaneously:
| Industry | Typical Application |
|---|---|
| ⚙️ Mechanical & Industrial Equipment | Machine frames, gearbox covers, hydraulic manifolds, heavy-duty access panels — Class 10.9 strength handles high preload requirements |
| 🚗 Automotive & EV | Chassis brackets, battery pack enclosures, motor mounts, suspension components — high vibration demands both 10.9 strength and spring washer retention |
| 🚲 Cycling & Powersports | Frame joints, handlebar clamps, brake caliper mounts — black finish matches anodized components; high strength ensures safety-critical retention |
| 🏗️ Steel Structure & Fabrication | Structural steel connections, equipment skids, modular frames — 10.9 grade provides high clamping force with compact button head profile |
| 🖥️ Electronics & Server Infrastructure | Heavy rack-mount equipment, UPS systems, industrial enclosures — black finish reduces glare; high strength secures heavy components |
| 🎮 Consumer Electronics & Robotics | Robot joints, drone frames, gaming peripherals — black oxide finish provides stealth aesthetics; tri-combination ensures reliable retention under vibration |
🏭 Direct Manufacturer — Full in-house production from wire drawing to finished tri-combination assembly
📐 Strict Dimensional Control — 100% inspection against ISO 7380, GB/T 9074.24, and GB/T 9074.26 standards
📦 Flexible MOQ — Bulk packs, reels, and custom packaging available
🌍 Global Export Experience — Shipped to 40+ countries with full documentation
📋 Full Traceability — Material certs, hardness test reports, and RoHS declarations on request
⚡ Fast Lead Times — Standard sizes in stock; custom lengths within 7–15 days
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