Product Overview This product is a high-strength hex head bolt manufactured from alloy steel (typically 42CrMo or SCM435) in Property Class 12.9 per ISO 898-1 — the highest standard strength grade for metric fasteners. The bolt features a standard hexagon head with metric coarse thread M16 × 2.0, and is finished with black oxide (blackening) surface treatment. The product conforms to DIN 931 (partial thread) and DIN 933 (full thread) dimensional standards, with additional sizes from M8 to M36 available on request. The Grade 12.9 designation indicates a minimum tensile strength of 1,220 MPa and a minimum yield strength of 1,100 MPa, making these bolts suitable for the most demanding high-tensile applications in heavy machinery, structural steel, mold/die tooling, and oil & gas equipment. The black oxide finish provides a sleek, oil-free black appearance while eliminating the hydrogen embrittlement risk associated with electroplating — a critical safety advantage for high-strength fasteners. Black oxide treatment is the preferred surface finish for high-strength bolts (Grade 8.8–12.9) in global OEM industries, driven by metallurgy, mechanical performance, thread precision, and long-term joint reliability. Material & Strength Grade Parameter Details Material Alloy steel (42CrMo, SCM435, 35CrMo) Grade 12.9 per ISO 898-1 Tensile Strength (min.) ≥ 1,220 MPa Yield Strength (min.) ≥ 1,100 MPa Proof Load ≥ 970 MPa Hardness HRC 39–44 (approximately 385–435 HV) Yield-to-Tensile Ratio 0.9 Chemical Composition C 0.37–0.41%, Cr 0.90–1.20%, Mo 0.15–0.30% Grade 12.9 bolts are manufactured from quenched and tempered alloy steel and achieve a minimum tensile strength of 1,220 MPa with hardness of 38–44 HRC. 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. 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. Standards & Specifications Parameter Details Product Type High-Strength Hex Head Bolt (Partially / Fully Threaded) Dimensional Standards DIN 931 (partial thread) / DIN 933 (full thread) / ISO 4014 / ISO 4017 / ASME B18.2.1 Material Standard ISO 898-1 Thread Size M16 × 2.0 (standard); M8–M36 available Thread Tolerance 6g (metric) Length Range 30 mm – 300 mm (customizable) Surface Finish Black Oxide (standard) / Plain Product Grade A / B DIN 931 specifies partially threaded hexagon head bolts with a plain shank, while DIN 933 specifies fully threaded hexagon head bolts. Both standards cover metric coarse threads from M6 to M36 in product grades A and B. ISO 4014 (partial thread) and ISO 4017 (full thread) are the international equivalents and are dimensionally interchangeable with DIN 931/933. Key Dimensions (Reference — DIN 933 / ISO 4017) Thread Size (d) Pitch (P) mm Width Across Flats (s) mm Head Height (k) mm Thread Length (b) M10 1.5 16.0 6.4 Full thread M12 1.75 18.0 7.5 Full thread M16 2.0 24.0 10.0 Full thread M20 2.5 30.0 12.5 Full thread M24 3.0 36.0 15.0 Full thread M30 3.5 46.0 18.7 Full thread All dimensions are in accordance with DIN 931 / DIN 933 / ISO 4014 / ISO 4017 standards. For partially threaded (DIN 931) configurations, the thread length (b) is determined by the nominal length (L) per the standard. Mechanical Properties (Reference — Grade 12.9) Size Tensile Strength (MPa) Yield Strength (MPa) Proof Load (MPa) Hardness M10 1,220 1,100 970 385–435 HV M12 1,220 1,100 970 385–435 HV M16 1,220 1,100 970 385–435 HV M20 1,220 1,100 970 385–435 HV M24 1,220 1,100 970 385–435 HV M30 1,220 1,100 970 385–435 HV Grade 12.9 bolts 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 black oxide Grade 12.9 bolts is approximately 300°C. Black Oxide Surface Treatment Parameter Specification Coating Thickness 0.5–1.5 μm Salt Spray Resistance 24–96 hours (to red rust, oiled) Appearance Deep black, uniform matte finish Corrosion Mechanism Barrier protection (no sacrificial protection) Maximum Service Temperature ~300°C (continuous) Lubricity Enhanced — improves torque-tension consistency Hydrogen Embrittlement Risk None — no acid pickling or electrolysis Black oxide is a conversion coating produced by chemical reaction between the steel surface and oxidizing salts, forming a dense magnetite (Fe₃O₄) layer of 0.5–1.5 μm thickness. The low-temperature surface conversion process operates at approximately 140–180°C, ensuring no alteration of the quenched-and-tempered microstructure and no degradation of mechanical properties. Key advantages of black oxide for Grade 12.9: No hydrogen embrittlement risk — unlike electroplating, black oxide does not introduce hydrogen into the steel Preserves thread geometry — thin coating requires no post-coating thread re-tapping Maintains preload accuracy — consistent torque-tension relationship for friction-based joints Enhanced lubricity — reduces friction during tightening Important note for Grade 12.9: Grade 12.9 bolts have hardness above 320 HV and are particularly susceptible to hydrogen embrittlement when electroplated. Black oxide is the preferred surface treatment precisely because it avoids this risk entirely. Industry guidance explicitly states that Grade 12.9 screws typically undergo black oxide treatment rather than electroplating. Torque Specifications (Grade 12.9, Black Oxide) Size Recommended Tightening Torque (N·m) Tightening Torque (ft-lb) 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 = 0.12–0.14 (black oxide, lightly oiled). Black oxide provides enhanced lubricity compared to plain steel, which may reduce the friction coefficient and require adjusted torque values. For critical assemblies, validate the tightening method, friction, and preload on the actual joint using ISO 16047 torque-tension testing. Applications Grade 12.9 black oxide hex head bolts are widely used across industries: Structural Steel & Construction — Beam-to-column connections, bracing, column base anchoring, bridge connections Heavy Machinery — Presses, cranes, excavators, mining equipment, wind turbine components Mold & Die Tooling — Mold base assembly, ejector plate fastening, die clamping Oil & Gas Facilities — Wellhead equipment, pipeline flanges, pump and compressor mounting Power Generation — Turbine mounting, generator anchoring, transmission tower connections Automotive & Powertrain — Engine components, transmission housings, chassis connections Industrial Equipment — Injection molding machines, hydraulic equipment, CNC machine assembly Regional insight: In the Middle East, Grade 12.9 hex head bolts are particularly common in oil & gas valve and instrument assembly, heavy machinery installation, and structural steel connections where maximum load capacity is required. The black oxide finish provides a sleek appearance and adequate corrosion protection for indoor and protected environments. For coastal or outdoor applications, Dacromet (zinc-flake) coating is recommended as an alternative that provides superior corrosion resistance without hydrogen embrittlement risk. Quality Assurance All products are manufactured under strict quality control procedures in accordance with ISO 898-1 (mechanical properties of fasteners), DIN 931 / DIN 933, and ISO 4014 / ISO 4017 standards. Quality control steps performed on each production batch: Chemical composition verification of the alloy steel material Tensile testing of the bolt body Hardness testing to confirm 39–44 HRC for 12.9 grade Impact testing for toughness verification Thread gauge inspection (go/no-go gauges) for 6g tolerance Visual inspection for surface defects and black oxide coating uniformity 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. Packaging & Customization Export Packing: Carton / wooden case / steel pallet Domestic Packing: Standard corrugated box / plastic bag / bulk carton OEM/ODM: Available — custom sizes, thread types (metric / UNC / UNF / BSW), materials (alloy steel, carbon steel), and surface finishes (zinc plated, Dacromet, plain) can be produced according to drawings or samples