What Types of Bolts Are Used in Guardrail and Road Safety Systems?

Guardrails are critical components in modern road safety infrastructure, serving as protective barriers that reduce the severity of accidents. But not all bolts are created equal. Understanding the different types of guardrail bolts used in these systems is essential for ensuring both structural integrity and long-term durability.

In this article, we’ll explore the types of bolts commonly used in guardrail systems, their functions, standard specifications, coating options, and how to choose the right ones for your project.

Fasteners used in highway and roadside barriers must withstand:

• Constant vibration from passing vehicles
• Exposure to rain, snow, de-icing salt, and UV radiation
• Dynamic impact loads during collisions

Unlike typical bolts, guardrail bolts must provide strength, corrosion resistance, and compatibility with safety certification standards like AASHTO M180, EN1317, or MASH.

Here are the most widely used bolt types in guardrail systems:

Use: W-beam guardrails, blockouts, and splice connections

Typical Specs: ASTM A307 Grade B, HDG finish

Features:

• Smooth domed head for tamper resistance
• Square neck under the head prevents turning during tightening
• Often used where exposed heads should be low-profile and snag-free

Use: Post-to-beam connections, terminal end systems, box beam guardrails

Typical Specs: ASTM A325, ISO 4017

Features:

• Strong clamping force, good for structural areas
• Easy torque control with wrench
• Used where frequent maintenance may be required

Use: High-load connections, guardrail to steel post

Typical Specs: DIN 6921, ASTM F3125

Features:

• Built-in washer increases bearing surface
• Reduces need for separate washer components
• Ideal for time-saving in roadside installations

Use: Breakaway signposts, crash cushions, high-speed barrier systems

Typical Specs: Custom / project-specific

Features:

• Designed to fail under set impact force
• Protects larger structure or redirects energy
• Often found in guardrail terminal ends or sign mounting kits

Since guardrail fasteners are constantly exposed to the elements, corrosion protection is essential. Common coating types include:

Coating Type	Description	Use Case
Hot-Dip Galvanized (HDG)	Thick, durable zinc layer (≥50μm)	Most highway applications
Zinc-Plated (Electroplated)	Shiny but thinner coating (<10μm)	Not recommended for outdoor use
Mechanical Galvanizing	Uniform, impact-free zinc application	When thread fit is critical
Weathering Steel / Corten	Rust-stabilizing steel	Select regional guardrail systems
Stainless Steel (304/316)	High corrosion resistance	Coastal zones or tunnels

Tip: For compliance with AASHTO M180 or EN1317, HDG bolts are typically required.

Guardrail bolts are usually short in length (≤100mm) and fully threaded, to ensure full engagement in compact structural profiles.

Don’t forget:

• Matching nuts (hex or flange, HDG)
• Washers (flat or curved) for bearing area and vibration resistance
• Locking devices (if anti-loosening is required in impact-prone zones)

Depending on your project location, guardrail bolts may need to comply with:

Region	Standard	Notes
USA	AASHTO M180, MASH, ASTM A307	Most DOT highway projects
EU	EN 1317, CE Marking	Common in European guardrail systems
Australia	AS/NZS 3845	Includes bolt performance for crash rails
Middle East & SE Asia	Based on ASTM / ISO hybrid	Often requires MTC + 3rd-party testing

TUHU Fasteners offers bolts with full mill test certificates (MTCs) and optional third-party inspections.

When selecting guardrail bolts, consider the following:

• System Type: W-beam, box beam, cable barrier, crash cushion
• Material Compatibility: Match zinc-coated steel to galvanized structures
• Certification Needs: Public road projects may require CE, AASHTO, or EN compliance
• Ease of Installation: Flange bolts may reduce on-site labor
• Environmental Exposure: Choose HDG or stainless for marine or snow belt regions

Guardrail bolts may seem like minor components, but their role is critical in ensuring the structural integrity and safety performance of road barrier systems. By selecting the right bolt type, coating, and standard, you’re protecting not just steel structures—but lives.

We manufacture and supply:

• HDG carriage bolts
• Guardrail hex bolts
• Anchor bolts

With global shipping, MTCs, and full standard compliance.

📞 Contact us to request a quote or compliance specification.

👉 Explore TUHU Guardrail Fasteners