Product Overview This product is a high-strength hex socket head cap screw (also known as a socket head cap screw, Allen bolt, or cup head screw), manufactured from high-grade alloy steel in Property Class 12.9 per ISO 898-1 — the highest standard strength grade for metric fasteners. It features a cylindrical head with a hexagonal socket drive and a zinc-plated (blue-white) finish for corrosion protection. The screw conforms to DIN 912 / ISO 4762 dimensional standards and is available in thread sizes from M3 to M36 (M42–M64 on request). The 12.9 grade designation indicates a minimum tensile strength of 1,220 MPa (177,000 psi) and a yield strength of 1,100 MPa (160,000 psi) — making these screws suitable for the most demanding high-tensile applications in machinery, automotive, aerospace, and structural engineering. The hexagonal socket drive allows for higher torque transmission than external hex or Phillips drives, enables compact head profiles for recessed applications, and provides precise alignment during installation. Material & Strength Grades Grade Material Tensile Strength (min.) Yield Strength (min.) Hardness Typical Applications 8.8 Medium carbon steel (45#, 10B21) ≥800 MPa ≥640 MPa 250–320 HB General machinery, structural 10.9 Alloy steel (35CrMo, 40Cr, SCM435) ≥1,040 MPa ≥940 MPa 320–380 HV Heavy machinery, automotive 12.9 Alloy steel (42CrMo, SCM435) ≥1,220 MPa ≥1,100 MPa 385–435 HV Critical high-strength applications Grade 12.9 bolts are manufactured from quenched and tempered alloy steel (typically 42CrMo or SCM435) and achieve a minimum tensile strength of 1,220 MPa with hardness of 38–44 HRC (approximately 385–435 HV). The "12.9" designation indicates the minimum tensile strength is approximately 1,220 MPa (12 × 100 = 1,200 MPa nominal) and the yield-to-tensile ratio is 0.9 (1,220 × 0.9 ≈ 1,100 MPa). Grade 12.9 provides approximately 50% higher tensile strength than Grade 8.8 and 17% higher than Grade 10.9, making it the preferred choice for critical high-stress applications where maximum load capacity is required. The material composition typically includes 0.37–0.41% carbon, 0.90–1.20% chromium, and 0.15–0.30% molybdenum for through-hardening capability. Standards & Specifications Parameter Details Product Type Hex Socket Head Cap Screw (Cylindrical Head) Standard DIN 912 / ISO 4762 / BS 4168 / UNI 5931 / JIS B 1176 Thread Size M3, M4, M5, M6, M8, M10, M12, M16, M20, M24, M30, M36 (M42–M64 on request) Thread Pitch M3×0.5, M4×0.7, M5×0.8, M6×1.0, M8×1.25, M10×1.5, M12×1.75, M16×2.0, M20×2.5, M24×3.0 Length Range 6 mm – 300 mm (customizable) Thread Tolerance 6g (metric) Material Alloy steel: 42CrMo / SCM435 / 35CrMo Surface Finish Zinc Plated (Blue-White / Clear / Yellow) Drive Type Hexagonal socket (Allen key) Product Grade A (per ISO 4762) DIN 912 is the classic German standard for hex socket head cap screws, covering metric coarse threads from M1.6 to M64 in product grade A. ISO 4762 is the international equivalent and has replaced DIN 912 as the primary standard. DIN 912 and ISO 4762 screws are interchangeable — they share the same dimensions and properties, with ISO 4762 incorporating updated wrench-size tolerances and the addition of stainless steel grades A3–A5. BS 4168 (British Standard) and UNI 5931 (Italian Standard) are national equivalents that are dimensionally compatible with DIN 912 / ISO 4762. JIS B 1176 is the Japanese equivalent. Key Dimensions (Reference) Thread Size (d) Pitch (P) mm Head Diameter (dk) mm Head Height (k) mm Hex Socket (s) mm Key Engagement (t) mm M3 0.5 5.5 3.0 2.5 1.3 M4 0.7 7.0 4.0 3.0 2.0 M5 0.8 8.5 5.0 4.0 2.5 M6 1.0 10.0 6.0 5.0 3.0 M8 1.25 13.0 8.0 6.0 4.0 M10 1.5 16.0 10.0 8.0 5.0 M12 1.75 18.0 12.0 10.0 6.0 M16 2.0 24.0 16.0 14.0 8.0 M20 2.5 30.0 20.0 17.0 10.0 M24 3.0 36.0 24.0 19.0 12.0 M30 3.5 45.0 30.0 22.0 15.0 M36 4.0 54.0 36.0 27.0 18.0 All dimensions are in accordance with DIN 912 / ISO 4762 standards. Mechanical Properties (Reference) Size Grade Tensile Strength (MPa) Yield Strength (MPa) Hardness Proof Load (MPa) M6 12.9 1,220 1,100 385–435 HV 970 M8 12.9 1,220 1,100 385–435 HV 970 M10 12.9 1,220 1,100 385–435 HV 970 M12 12.9 1,220 1,100 385–435 HV 970 M16 12.9 1,220 1,100 385–435 HV 970 M20 12.9 1,220 1,100 385–435 HV 970 M24 12.9 1,220 1,100 385–435 HV 970 Grade 12.9 socket head cap screws achieve a minimum tensile strength of 1,220 MPa and a minimum proof load of 970 MPa. The Rockwell C hardness typically ranges from 39 to 44 HRC. The maximum operating temperature for unplated Grade 12.9 screws is 300°C; zinc-plated versions have a maximum service temperature of approximately 150–200°C depending on the coating system. Zinc Plating & Corrosion Protection Finish Coating Thickness Salt Spray Resistance Recommended Environment Zinc Plated (Blue-White) 8–12 μm 72–144 hours Indoor, general industrial Zinc Plated (Yellow) 8–12 μm 96–168 hours Outdoor, moderate corrosion Zinc Plated (Clear) 5–8 μm 48–96 hours Indoor, temporary protection Zinc-Nickel Plated 8–12 μm 500–1,000+ hours Coastal, automotive, high-corrosion Dacromet (Reference) 5–12 μm 600–1,500+ hours Coastal, offshore, high-corrosion Zinc plating provides sacrificial (cathodic) protection to the underlying alloy steel. The zinc coating corrodes preferentially, protecting the steel substrate from rust. The standard blue-white zinc plating provides good corrosion protection for indoor and general industrial applications. Important note on hydrogen embrittlement: Due to their high hardness (≥320 HV), Grade 12.9 screws are susceptible to hydrogen embrittlement when electroplated. Per ISO 4042, fasteners with hardness above 320 HV require post-coating baking at 190–220°C for 4–24 hours to relieve hydrogen. For critical applications in coastal or offshore environments, Dacromet or zinc-flake coatings are recommended as alternatives that eliminate hydrogen embrittlement risk entirely. Torque Specifications (Grade 12.9, Zinc Plated) Size Recommended Tightening Torque (N·m) Recommended Tightening Torque (ft-lb) M4 3.0 2.2 M5 5.5 4.1 M6 10.0 7.4 M8 25.0 18.4 M10 48.0 35.4 M12 86.0 63.4 M16 210.0 154.9 M20 410.0 302.4 M24 710.0 523.7 Torque values assume μ = 0.12 (zinc-plated, unlubricated). For lubricated or coated fasteners, adjust torque accordingly. Applications Grade 12.9 socket head cap screws are widely used in applications requiring maximum strength, precise clamping, and compact head profiles: Machine Tool & Equipment Assembly — Spindle mounting, tool holder clamping, fixture assembly Automotive & Powertrain — Engine components, transmission housings, chassis connections Aerospace & Defense — Airframe structural fastening, engine mounts, avionics brackets Industrial Machinery — Presses, CNC machines, molding equipment, hydraulic systems Mold & Die Making — Mold base assembly, ejector plate fastening, die clamping Robotics & Automation — Robot arm joints, linear motion guides, end effector mounting Energy & Power Generation — Turbine components, generator mounting, switchgear assembly Medical & Precision Equipment — Surgical instruments, diagnostic equipment, optical mounts Bicycle & Motorcycle — Stem bolts, brake calipers, disc rotor mounting Racing & Performance — Suspension components, engine mounts, chassis bracing The compact cylindrical head allows the screw to be used in recessed or counterbored holes where an external hex head would not fit. The hex socket drive enables higher torque transmission with a smaller wrench size, making these screws ideal for tight spaces and precision assemblies. Packaging & Customization Export Packing: Carton / wooden case / steel pallet Domestic Packing: Standard corrugated box / bag OEM/ODM: Available — custom sizes, thread types, materials, strength grades, and surface finishes can be produced according to drawings or samples MOQ: Negotiable Quality Assurance All products are manufactured under strict quality control procedures in accordance with ISO 898-1 (mechanical properties of fasteners), ISO 4762 / DIN 912, and ISO 4042 (electroplated coatings). The product has achieved a 100% positive review rate with a 50% repurchase rate on the platform, reflecting consistent quality and customer satisfaction. Material test certificates (EN 10204 3.1), dimensional inspection reports, hardness test reports, and third-party inspection reports (SGS, BV, CTI) can be provided upon request. For Grade 12.9 screws, tensile testing, hardness testing, and hydrogen embrittlement relief verification are performed on each production batch. Ordering Information To place an order or request a quotation, please specify: Product type — Hex socket head cap screw (DIN 912 / ISO 4762) Standard — DIN 912 / ISO 4762 / BS 4168 / JIS B 1176 Material — Alloy steel (42CrMo / SCM435 / 35CrMo) Strength grade — 8.8 / 10.9 / 12.9 Thread size and pitch — e.g., M8 × 1.25 or M12 × 1.75 Length — Specify total length (e.g., 20 mm, 30 mm, 50 mm) Surface finish — Zinc plated (specify color) / Zinc-nickel / Dacromet / Plain Quantity — With any tolerance for over/under shipment Certification — EN 10204 3.1 MTC / ISO 898-1 compliance / SASO (for Saudi Arabia) / GOST-K (for Kazakhstan) Special requirements — Thread tolerance, marking, packaging, hydrogen embrittlement test report, etc.