Hex Bolts Technical Datasheets

The primary difference is the thread length. DIN 931 (ISO 4014) hex bolts have a partial thread, leaving a smooth shank between the head and the threaded portion, whereas DIN 933 (ISO 4017) hex bolts are fully threaded along their entire length. Partial thread bolts are often preferred where the joint is subjected to shear loads, while full thread bolts provide maximum thread engagement.

A full thread hex bolt (DIN 933 / ISO 4017) should be used when maximum thread engagement is required or when fastening into tapped holes. They are commonly used in machinery, fabrication, maintenance, and general industrial assemblies where the entire bolt length contributes to clamping.

Partial thread hex bolts (DIN 931 / ISO 4014) are preferred when the joint experiences significant shear forces. The unthreaded shank provides better alignment and improved shear strength compared to the threaded section, making them suitable for structural and heavy-duty mechanical applications.

Property Class 8.8 indicates a medium carbon steel bolt that has been heat-treated for higher strength. It has a minimum tensile strength of 800 MPa and a yield strength equal to 80% of its tensile strength (640 MPa). Class 8.8 is the most commonly used strength grade for industrial applications.

Property Class 8.8 offers higher mechanical strength than A2-70 stainless steel, making it suitable for heavy-duty applications. A2-70 stainless steel provides superior corrosion resistance but has lower tensile strength. The choice depends on whether strength or corrosion resistance is the primary requirement.

Hex bolts may be reused if they have not been permanently stretched, damaged, corroded, or subjected to critical loading conditions. However, for structural, safety-critical, or high-strength applications, replacing the bolt after removal is generally recommended to ensure joint integrity.

The recommended tightening torque depends on the bolt diameter, property class, lubrication, and surface finish. Always refer to the manufacturer’s torque specifications or recognised engineering standards, as applying incorrect torque can lead to bolt failure, thread stripping, or joint loosening.

In most cases, DIN 933 corresponds to ISO 4017, and DIN 931 corresponds to ISO 4014. Their dimensions are nearly identical for most practical applications, making them interchangeable in many engineering assemblies. However, critical applications should always verify dimensional and tolerance requirements.

The best coating depends on the operating environment. Hot-dip galvanizing is widely used for outdoor structural applications, while Geomet® and Dacromet® coatings provide excellent corrosion resistance without introducing hydrogen embrittlement. For highly corrosive environments, stainless steel A4 (316) is often the preferred choice.

Hex bolt length is measured from the underside of the head to the end of the threaded shank. The correct length should provide sufficient thread engagement while allowing the nut to fully engage without excessive thread projection.

Washers are recommended in many applications because they distribute the clamping force, protect the mating surface, and reduce the risk of loosening. However, whether a washer is required depends on the joint design, surface material, and engineering specifications.

Hex bolts are widely used across industries including construction, structural steel fabrication, automotive, industrial machinery, electrical equipment, renewable energy, telecommunications, agricultural equipment, railways, marine, oil & gas, and general manufacturing due to their versatility and high load-carrying capability.