Heavy Hex Structural Bolt

Heavy Hex Structural Bolt

High-strength heavy hex bolts for steel structures are friction-type connection assemblies specially designed for steel structure projects, manufactured in strict accordance with Chinese national standard GB/T 1231‑2024. A complete assembly consists of 1 bolt, 1 nut and 2 high-strength washers. Loads are transferred by friction between plates generated by bolt pre-tension. They serve as core fasteners for beam-column connections and joint splicing of steel members. Different from ordinary hex bolts, they feature enlarged and thickened heads. With quenching and tempering heat treatment, they deliver high tensile strength, shear resistance and fatigue resistance, and are widely used in various heavy-load steel structure engineering projects.

Material & Performance Grades

Main materials: 20MnTiB, 35VB alloy structural steel. Subjected to quenching and tempering heat treatment for uniform and stable grain structure with reliable mechanical properties, effectively preventing fracture and delayed cracking.

Performance grades: 8.8S and 10.9S. Grade 10.9S is most widely adopted in engineering. 10.9S features minimum tensile strength ≥1040MPa and minimum yield strength ≥940MPa. It resists loosening and deformation under heavy-load and vibration conditions.

Common sizes: M12, M16, M20, M22, M24, M27, M30. Non-standard lengths available upon request.

Surface treatments: Phosphating & blackening (standard for engineering), hot-dip galvanizing, Dacromet, zinc-aluminium coating, suitable for indoor, outdoor, humid and corrosive environments.

Product Features

Matched sets with controllable torque coefficient Complete connection assemblies are manufactured and inspected as matched sets. Torque coefficients fall within standard ranges to ensure accurate pre-tension during installation. Torque wrenches shall be used for initial tightening, re-tightening and final tightening. Torque coefficients can be tested to meet project acceptance requirements.

Safe and stable connection with vibration and slip resistance Load transfer via friction. The joints resist loosening under dynamic loads and cyclic vibration with controllable slip coefficient, guaranteeing overall structural safety of steel buildings and infrastructure projects for long service life.

Suitable for complex construction conditions Heavy hex head design compatible with standard torque wrenches. Compared with twist-off bolts, they perform better in confined spaces and for replacement during maintenance, convenient for disassembly, re-inspection and servicing at later stages.

Strict quality control Full inspections of hardness, torque coefficient and tensile load are completed before delivery. Third-party inspection and acceptance are supported. Grade marking is stamped on bolt heads for traceability, complying with steel structure construction codes.

Application Scope

✅ Industrial buildings: Beam-column joints of steel workshops, factories, warehouses, space trusses and pipe trusses ✅ Construction projects: High-rise steel structures, exhibition venues and large complex steel member splicing ✅ Transportation infrastructure: Highway & railway bridges, towers, lighting poles and steel trestles ✅ Other fields: Support frames for lifting equipment, photovoltaic steel supports, steel bases for large machinery and municipal steel structure projects

Construction Notes

Bolts shall be freely inserted into holes. Forced hammering or reaming is prohibited. Bolts at one joint shall be installed with consistent insertion direction. The chamfered side of washers shall face the bearing surfaces of bolt heads and nuts; reverse installation is not allowed. Professional torque wrenches are mandatory. Installation shall follow three steps: initial tightening, re-tightening and final tightening. Torque recheck is required after completion. Do not mix bolts, nuts and washers from different batches to avoid abnormal torque coefficients.

Packaging & Supply

Packed in cartons or wooden cases and counted by assembly, with product certificates supplied. Standard sizes in stock, custom dimensions and special anti-corrosion finishes available. Bulk supply for engineering projects is supported.