Product Overview This product is a high-strength, extra-long, heavy-duty hex head bolt manufactured from high-grade alloy steel (35CrMo, 40Cr, 42CrMo) or medium carbon steel (45#, 10B21), available in Grade 8.8, 10.9, and 12.9 per ISO 898-1. Designed for demanding structural, industrial, and pressure-boundary applications, these bolts feature a large hexagon head, extended lengths, and superior tensile strength — making them suitable for steel structures, bridges, pressure pipelines, heavy machinery, and offshore installations where standard bolts are insufficient. The product line includes fully threaded (DIN 933 / ISO 4017) and partially threaded (DIN 931 / ISO 4014) configurations, with thread sizes ranging from M6 to M100 (and imperial equivalents), and lengths from 20 mm to 1,500 mm or more. Custom sizes and non-standard dimensions are available upon request. Product Type & Design Feature Description Product Type High-Strength Hex Head Bolt / Heavy Hex Bolt / Extra-Long Hex Bolt Head Type Standard hexagon head (larger head size for heavy hex configurations) Thread Configuration Full thread (DIN 933 / ISO 4017) or partial thread (DIN 931 / ISO 4014) Thread Direction Right-hand (left-hand available on request) Thread Tolerance 6g (metric) / Class 2A (imperial) The large hexagon head provides a greater bearing surface and allows for higher torque transmission, reducing the risk of head damage during tightening. The extra-long shank enables the bolt to pass through thick flanges, deep structural members, or multiple components in a single connection. For heavy hex bolts, the head dimensions are intentionally oversized compared to standard hex bolts to distribute clamping loads over a wider area and prevent local yielding or crushing of softer flange materials under extreme preload conditions. 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 Steel structures, bridges, general machinery 10.9 Alloy steel (35CrMo, 40Cr, SCM435) ≥1,040 MPa ≥940 MPa 320–380 HV Heavy machinery, pressure vessels, offshore 12.9 Alloy steel (42CrMo, SCM435) ≥1,220 MPa ≥1,100 MPa 385–435 HV Critical high-strength structural, bridge connections Grade 8.8 bolts achieve a minimum tensile strength of 800 MPa and yield strength of 640 MPa, with the "8" representing approximately 1/100 of the minimum tensile strength in MPa and the ".8" indicating a yield-to-tensile ratio of 0.8. Grade 10.9 bolts provide 1,040 MPa minimum tensile strength and 940 MPa minimum yield strength, while Grade 12.9 bolts achieve 1,220 MPa minimum tensile strength and 1,100 MPa minimum yield strength. Material composition: Grade 8.8 — Medium carbon steel (45#, 10B21) with quenching and tempering Grade 10.9 — Alloy steel (35CrMo, 40Cr, SCM435) with controlled heat treatment Grade 12.9 — Alloy steel (42CrMo, SCM435) with precision heat treatment for maximum strength and toughness Standards & Specifications Parameter Details Product Type High-Strength Hex Head Bolt / Heavy Hex Bolt / Extra-Long Bolt Standards DIN 931 / DIN 933 / DIN 6914 / ISO 4014 / ISO 4017 / ASTM A325 / ASTM A490 / GB/T 5782 / GB/T 5783 Thread Sizes M6, M8, M10, M12, M16, M20, M24, M30, M36, M42, M48, M56, M64, M72, M80, M90, M100 Length Range 20 mm – 1,500 mm (custom lengths available) Thread Types Metric coarse / Metric fine / UNC / UNF / BSW Surface Finish Black oxide / Zinc plated / Hot-dip galvanized / Dacromet / Plain Product Grade A / B (per DIN / ISO) 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. DIN 6914 covers high-strength structural bolting with large hexagon head for preloaded joints, primarily used in steel structures. ASTM A325 and ASTM A490 are the primary US standards for heavy hex structural bolts, with A490 bolts matching ISO 12.9 territory at approximately 1,220 MPa tensile strength. Heavy hex bolts to these standards are universally specified for high-pressure pipeline flanges and petrochemical vessels. Key Dimensions (Reference) Thread Size (d) Pitch (P) mm Width Across Flats (s) mm Head Height (k) mm Max Length (mm) M6 1.0 10.0 4.0 300 M8 1.25 13.0 5.3 400 M10 1.5 17.0 6.4 500 M12 1.75 19.0 7.5 600 M16 2.0 24.0 10.0 800 M20 2.5 30.0 12.5 1,000 M24 3.0 36.0 15.0 1,200 M30 3.5 46.0 18.7 1,500 M36 4.0 55.0 22.5 1,500 All dimensions are in accordance with DIN 931 / DIN 933 and ISO 4014 / ISO 4017 standards. Mechanical Properties (Reference) Size Grade Tensile Strength (MPa) Yield Strength (MPa) Hardness M16 8.8 800 640 250–320 HB M16 10.9 1,040 940 320–380 HV M20 10.9 1,040 940 320–380 HV M24 10.9 1,040 940 320–380 HV M24 12.9 1,220 1,100 385–435 HV M30 12.9 1,220 1,100 385–435 HV M36 12.9 1,220 1,100 385–435 HV Grade 10.9 bolts exhibit a yield-to-tensile ratio of approximately 0.90, while Grade 12.9 bolts achieve approximately 0.90 with significantly higher absolute strength values. The mean yield strength of 12.9 steel is approximately 17% higher than 10.9 steel, with the ultimate strength increasing by approximately 16%. Surface Finish Options Finish Coating Thickness Salt Spray Resistance Recommended Environment Black Oxide 1–2 μm 24–48 hours Indoor, machinery, tooling Zinc Plated 8–12 μm 72–144 hours Indoor, general industrial Hot-Dip Galvanized (HDG) 45–85 μm 500–1,500+ hours Outdoor, coastal, marine, heavy structural Dacromet 5–12 μm 600–1,500+ hours Coastal, offshore, high-corrosion Plain — 24–48 hours Temporary, indoor For heavy structural applications, hot-dip galvanizing to ASTM A153 or ISO 1461 is the preferred finish, providing a thick, metallurgically bonded zinc coating that offers both barrier and sacrificial protection. HDG hex bolts in Grade 8.8 are widely used for solar mounting and steel structures with coating thicknesses of 60–85 μm for extended service life. For Grade 10.9 and 12.9 bolts, Dacromet (zinc-flake) coating is recommended over electroplating, as it eliminates the risk of hydrogen embrittlement while providing superior corrosion resistance. Applications High-strength extra-long hex head bolts are widely used across industries: Steel Structure & Bridge Construction — Beam-to-column connections, bracing, column base anchoring, bridge girder fastening Pressure Pipelines & Flange Connections — Extended-length bolts are essential for "8" figure blind flanges, wafer valve flanges, non-standard flanges, and multi-nut fastening flanges in overseas oilfield surface engineering projects Oil & Gas Facilities — Wellhead equipment, pipeline flanges, pressure vessels, offshore platforms Heavy Machinery & Equipment — Presses, cranes, excavators, mining equipment, wind turbine components Power Generation — Turbine mounting, generator anchoring, transmission tower connections Petrochemical & Chemical Processing — Reactor vessels, heat exchangers, high-temperature piping Marine & Offshore — Platform structures, dock hardware, subsea equipment Bolt length is a critical factor in ensuring leak-free pressure pipeline flange connections. Extended-length bolts are specifically required for applications where the flange assembly includes insulating sleeves, multiple nuts, or non-standard flange thicknesses. Packaging & Customization Export Packing: Wooden box / crate / steel pallet Domestic Packing: Corrugated carton / bundle with strapping OEM/ODM: Available — custom sizes, thread types, materials, strength grades, and surface finishes can be produced according to drawings or samples Length Cutting: Bolts can be supplied in standard lengths or cut to specific dimensions MOQ: Negotiable Quality Assurance All products are manufactured under strict quality control procedures in accordance with ISO 898-1 (mechanical properties of fasteners), DIN, ISO, ASTM, and GB standards. 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 10.9 and 12.9 bolts, tensile testing, hardness testing, and impact testing are performed on each production batch. For hot-dip galvanized bolts, coating thickness verification is performed in accordance with ASTM A153 or ISO 1461. Ordering Information To place an order or request a quotation, please specify: Product type — Hex head bolt / Heavy hex bolt / Extra-long bolt Standard — DIN 931 / DIN 933 / DIN 6914 / ISO 4014 / ISO 4017 / ASTM A325 / A490 Material — Carbon steel (45#, 10B21) / Alloy steel (35CrMo, 40Cr, 42CrMo, SCM435) Strength grade — 8.8 / 10.9 / 12.9 Thread size and pitch — e.g., M20 × 2.5 or M30 × 3.5 Length — Specify total length and thread length if applicable Surface finish — Black oxide / Zinc plated / HDG / Dacromet / Plain Quantity — With any tolerance for over/under shipment Certification — EN 10204 3.1 MTC / SASO (for Saudi Arabia) / GOST-K (for Kazakhstan) Special requirements — Thread tolerance, marking, packaging, etc.