4.8 Grade - White zinc – Hexagon bolt

Technical Characteristics of Grade 4.8 Bolts

Grade 4.8 bolts are widely known in the industry as "mild steel" or "low carbon" fasteners. Unlike high-tensile bolts (like 8.8) which undergo quenching and tempering, Grade 4.8 fasteners rely on the natural properties of the low carbon steel wire and the cold-heading process. This results in a fastener that is tough and ductile, making it less brittle and significantly more affordable for projects that do not involve critical structural loads.

Understanding the "4.8" Designation

The marking "4.8" on the bolt head strictly defines the mechanical limits of the material under ISO standards:

The "4" - Nominal Tensile Strength

The first digit represents 1/100 of the tensile strength. Value: 4 × 100 = 400 N/mm². This is the maximum load the bolt can withstand before fracturing.

The ".8" - Yield Strength Ratio

The second digit indicates the yield point ratio. Value: 0.8 × 400 = 320 N/mm². This is the point where the bolt will permanently stretch. Because the yield point is relatively low, precise torque control is less critical than in high-strength applications, but care must still be taken not to over-tighten.

Ductility

A key advantage of Grade 4.8 is its elongation capacity. It can stretch significantly before breaking, providing a safe failure mode in non-structural applications.

Quality Assurance and Material Reports

At Fastener Core, we ensure our materials meet industry standards. For customers requiring documentation for their records, we are happy to supply an EN 10204 3.1 Material Test Certificate (MTC) verifying the chemical composition of the steel. Simply mention your requirement to our team during the ordering process, and we will arrange this for you.

Typical Applications

Grade 4.8 white zinc bolts are the preferred choice for sectors driven by cost and general utility:

• Light Assembly: Fastening covers, panels, and guards on machinery.
• Furniture Industry: Joining timber and composite materials where high clamping force would crush the wood.
• Cable Support: Securing conduit saddles and cable trays in building services.
• Shear Pins: Used in agricultural machinery to break under overload, protecting the gearbox.

Frequently Asked Questions

Can I weld Grade 4.8 white zinc bolts?

Grade 4.8 bolts are made from low carbon steel, which is chemically excellent for welding. However, the white zinc plating presents a safety hazard. Welding zinc-plated parts produces toxic fumes. You must remove the zinc plating (by grinding or acid cleaning) from the weld area before welding to ensure safety and weld quality.

Is Grade 4.8 suitable for hanging heavy loads?

Generally, no. For overhead lifting, suspension, or structural steel connections, Grade 8.8 is the minimum safety standard. Grade 4.8 should only be used for "secondary" connections where failure would not result in structural collapse or injury.

Does white zinc plating prevent rust outdoors?

White zinc plating provides a sacrificial barrier that works best in dry, indoor environments. While Grade 4.8 bolts are often used for temporary outdoor fixings, they will eventually rust if exposed to rain and humidity over time. For permanent outdoor use, hot-dip galvanized or stainless steel is preferred.