The Countersunk Socket Head Cap Screw (commonly referred to as a flat head socket screw or DIN 7991 Allen screw) is an essential high-tensile fastener engineered for applications requiring a completely flush, protrusion-free surface finish. Featuring a 90-degree conical head geometry and a precision internal hex drive, this fastener allows seamless countersunk installation in heavy machinery, precision tooling, automation equipment, and automotive structures in accordance with global ISO standards.
Technical Specifications of Countersunk Socket Head Cap Screw
Due to the reduced load-bearing cross-section under the conical countersunk head compared to standard cylindrical socket caps, DIN 7991 screws are manufactured from high-grade alloy steel (such as 40Cr, 35CrMo, or SCM435) to compensate with extreme tensile strength. Grade 10.9 achieves a minimum tensile strength of 1040 MPa, ensuring high torque capability and fatigue endurance without head snapping.
| Property Rating | Alloy Material Grade | Tensile Strength (Min) | Yield Strength (Min) | Head Angle / Hardness |
|---|---|---|---|---|
| Grade 8.8 | Medium Carbon Steel / 40Cr Steel | 800 N/mm² (800 MPa) | 640 N/mm² (640 MPa) | 90° Countersunk / 22–32 HRC |
| Grade 10.9 | Alloy Steel (40Cr / 35CrMo / SCM435) | 1040 N/mm² (1040 MPa) | 940 N/mm² (940 MPa) | 90° Countersunk / 32–39 HRC |
Precision Cold Heading and Thermal Processing for Countersunk Socket Head Cap Screw
At our manufacturing facility in Handan, China, every Grade 8.8 and 10.9 countersunk socket screw undergoes high-precision cold extrusion and continuous heat treatment to eliminate internal stresses:
- Conical Head & Internal Hex Cold Extrusion: Multi-station cold heading formers extrude the exact 90-degree conical head profile and deep internal hex socket, preventing Allen key slippage under high tightening torque.
- Controlled-Atmosphere Heat Treatment: Fasteners pass through computer-controlled mesh-belt furnaces for oil quenching and precise tempering to ensure consistent Rockwell hardness and high toughness.
- Precision Thread Rolling: Rolled metric 6g threads maintain smooth surface grain flow, reducing thread friction and preventing stripping in tapped blind holes.
- Surface Coating & Protection: Standard black oxide finish treated with anti-rust oil, with options for electro-zinc plating, Dacromet, or Geomet coatings.
Industrial Applications of Countersunk Socket Head Cap Screw
The flush flat-head profile makes countersunk hex socket screws ideal for assemblies where moving parts pass closely over the fastener head or where aesthetic smoothness is mandatory:
- Automation & CNC Machine Tools: Fastening linear guide rails, sliding plates, and machine covers where zero head clearance is permitted.
- Stamping Dies & Fixtures: Mounting wear plates, stripper pads, and precision tooling plates subjected to high dynamic impact.
- Automotive & Mechanical Assemblies: Securing internal engine covers, brake system brackets, and structural machine housings.
Quality Assurance and Export Packaging for Countersunk Socket Head Cap Screw
Handan YiHao Fastener enforces comprehensive Quality Control (QC) standards for all export orders. Testing procedures include 90° countersunk head angle measurement, Rockwell hardness (HRC) verification, internal hex socket gauge depth testing, and thread ring gauge checks.
All export shipments are packed in heavy-duty 25kg inner cartons, neatly stacked on ISPM 15 compliant fumigated wooden pallets, and wrapped in protective stretch film to prevent moisture damage during sea transport.
Request Factory Direct Pricing for Countersunk Socket Head Cap Screws
Looking for a trusted manufacturer in Handan, China for Grade 8.8 or 10.9 countersunk socket head cap screws (DIN 7991)? Contact Handan YiHao Fastener today for technical datasheets, CAD drawings, sample shipments, and competitive bulk factory quotes.
