An outer hexagon bolt, also known as an external hex bolt or hex head bolt, is a type of threaded fastener with a six-sided (hexagonal) head designed to be tightened or loosened using a wrench, spanner, or socket. It is widely used in construction, machinery, steel structures, automotive, and industrial assemblies where strong and reliable fastening is required.

Structure and Design Features

Hexagonal Head

The defining feature of an outer hexagon bolt is its external hex head, which allows for easy installation and removal using standard tools. The hex shape provides multiple contact points for applying torque, making it suitable for high-strength fastening applications.

Threaded Shaft

Outer hexagon bolts typically have machine threads, which allow them to be paired with nuts or inserted into tapped holes. They can be fully threaded or partially threaded, depending on the design and intended load-bearing use.

Common Standards

Outer hexagon bolts are manufactured according to international standards, ensuring consistency and compatibility:

• DIN 931 – Partial thread hexagon bolt

• DIN 933 – Fully threaded hexagon bolt

• ISO 4014 / ISO 4017 – Metric hex bolts

• ASTM A307 / ASTM A325 / ASTM A490 – Inch-size hex bolts for structural applications

Materials and Strength Grades

Outer hexagon bolts are available in a variety of materials to meet different mechanical and environmental requirements:

• Carbon Steel – Standard industrial applications

• Alloy Steel – High-strength assemblies

• Stainless Steel (SS304 / SS316) – Corrosion-resistant environments

Typical strength grades include 4.8, 6.8, 8.8, 10.9, and 12.9, with higher grades used in heavy-duty or structural applications.

Surface Treatments

To enhance corrosion resistance and durability, outer hexagon bolts can have various surface finishes:

• Zinc plated (white, yellow, or blue)

• Black oxide

• Hot-dip galvanized

• Plain / stainless steel natural finish

Applications

Outer hexagon bolts are widely used in industries such as:

• Construction and steel structures – Bridges, buildings, and infrastructure

• Machinery and equipment assembly – Industrial machines, conveyors, and presses

• Automotive and heavy vehicles – Engine components and chassis

• Energy and power installations – Turbines, pipelines, and structural supports

Their high-strength design and versatile installation options make them suitable for both structural and mechanical applications.