Understanding Screw Grades: Choosing the Right Bimetal Screws for Your Project

Why Screw Grades Matter

Screw grades indicate a fastener’s material composition, mechanical strength, and performance limits. They’re not just technical jargon—they guide engineers, procurement teams, and installers in choosing the right product for the right job.
In industrial projects, using the wrong grade can lead to premature failure, costly downtime, or even safety hazards. For example, a screw with insufficient tensile strength might strip or snap under load, while one with low corrosion resistance could deteriorate in months.
When it comes to bimetal screws, grade considerations become even more important because you are working with two distinct metals—commonly a stainless steel head for corrosion resistance and a hardened carbon steel drill point for strength.

What Screw Grades Actually Mean

Grades are essentially shorthand for a set of properties. For carbon steel screws, the grade often reflects tensile strength and hardness. For stainless steel, the “grade” is usually tied to its alloy composition, which impacts corrosion resistance and durability.

Below is a quick reference for common screw grades used in industrial bimetal applications:

Bimetal screws often combine a stainless steel grade like A2-70 for the head and shank with a carbon steel grade like 8.8 for the drill tip. This ensures both corrosion resistance and the ability to self-drill into structural steel.

Matching Grades to Application Needs

Choosing the right screw grade depends heavily on the environment and mechanical demands of your project.

• Marine & Offshore 🌊
  Saltwater exposure accelerates corrosion. For docks, ships, and offshore platforms, A4 stainless steel is the preferred choice for the head, paired with a hardened carbon steel tip to penetrate thick steel structures.
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• Roofing & Cladding 🏗
  Roofing projects require screws that can withstand wind uplift, temperature fluctuations, and UV exposure. Bimetal screws with an A2 stainless steel head and EPDM washer provide both structural reliability and leak prevention.

• Energy Sector & Heavy Industry ⚙️
  Wind turbines, oil rigs, and processing plants often require Grade 10.9 or higher carbon steel drill points for high torque applications. The stainless steel upper portion ensures resistance to environmental degradation.

Industry Standards and Compliance

When selecting screw grades, it’s worth checking whether your supplier adheres to recognized standards. Some of the most relevant include:

• ISO 3506 – Defines mechanical properties for stainless steel fasteners.

• ISO 898-1 – Covers mechanical properties for carbon steel bolts, screws, and studs.

• ASTM A193 / A320 – U.S. standards for alloy and stainless steel fasteners for high-temperature or pressure environments.

Working with a supplier that provides material certificates ensures you get exactly what’s specified, reducing the risk of mismatched or counterfeit fasteners.

Balancing Performance and Cost

Higher-grade screws generally cost more, but in high-risk or harsh environments, the investment often pays off in reduced maintenance and longer service life.
For instance, upgrading from A2 to A4 stainless might cost 15–20% more per unit, but in a marine setting, it can extend service life by several years—avoiding expensive replacements.

Final Thoughts

Understanding screw grades is crucial when sourcing bimetal screws for industrial projects. By considering tensile strength, corrosion resistance, and compliance with industry standards, you can ensure long-term performance and safety.

Have a similar project? Contact us to discuss the best screw type for your needs.

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