What are High Strength Hex Head Bolts?

What are High Strength Hex Head Bolts? (Full professional explanation for fastener foreign trade)

1. Basic Definition

High strength hex head bolts, also shortened as high-strength hex bolts, are heavy-duty external threaded fasteners with a hexagonal six-sided head, manufactured from alloy steel and treated with quenching & tempering heat treatment to achieve superior tensile and yield strength, far stronger than ordinary mild steel bolts (4.8 grade).
The hexagonal head allows stable tightening with spanners, socket wrenches or torque wrenches, which is essential for precise pre-tension required in heavy load scenarios.

2. Core Distinction from Regular Hex Bolts

1. Raw Material
Ordinary bolts: low carbon mild steel;
High strength hex bolts: medium carbon/alloy steel (45# steel, 40Cr, SCM435, 35CrMo).

2. Heat Treatment
High strength versions undergo quenching + tempering to boost hardness and anti-deformation capacity; regular bolts have no strict heat treatment.

3. Strength Grades (Main metric standards)

◦ 8.8 grade: tensile strength ≥800MPa

◦ 10.9 grade: tensile strength ≥1040MPa

◦ 12.9 grade: tensile strength ≥1220MPa
Common standard bolts are only 4.8 grade, with much lower bearing capacity.

4. Service Feature
High strength hex bolts rely on pre-tightening friction to transfer loads; they are non-reusable once disassembled, while common bolts can be reused multiple times.

3. Main Global Standards

• Metric Europe: DIN931 (semi-thread), DIN933 (full thread), DIN6914 structural hex bolts

• Chinese GB: GB5782, GB5783, GB/T1228 large hex structural bolts

• US ASTM: A325, A490 structural hex bolts; A193 B7 high-temperature high-strength studs

• International: ISO 4014, ISO 4017

4. Surface Treatments

• Zinc plating, black oxide, hot-dip galvanizing, Dacromet, mechanical galvanizing, for rust & corrosion resistance.

5. Typical Application Scenarios

Steel structure buildings, bridges, heavy machinery, truck chassis, wind power equipment, automotive assemblies, pressure vessels, railway engineering, industrial equipment with heavy vibration or dynamic loads.

6. Short Simple Version (for inquiry & product page)

High strength hex head bolts are heavy-load fasteners with hexagonal heads, made of alloy steel with complete heat treatment. Available in 8.8/10.9/12.9 strength grades complying with DIN, GB and ASTM standards. They withstand huge tension and shear force, widely used in construction, machinery, auto and steel structure projects. Matched hex nuts and washers are supplied together as sets.

7. Common Sentence Examples for Foreign Trade

1. We supply DIN933 M12×60 high strength hex head bolts in 10.9 grade.
我们供应10.9级DIN933 M12×60高强度外六角螺栓。

2. High strength hex head bolts require torque wrench installation to reach standard pre-tightening force.
高强度六角螺栓需使用扭矩扳手安装以达到标准预紧力。

3. SCM435 material is widely adopted for producing 12.9 grade high strength hex head bolts.
SCM435材质广泛用于生产12.9级高强度六角螺栓。