Our hardened thick flat washers (DIN 6916 / EN 14399-6) are heat-treated, extra-thick washers designed for high-strength structural bolted joints. Their hardness resists the indentation and deformation that would occur with a standard washer under high preload, maintaining bearing area and clamp force in steel construction, bridges, and heavy machinery.

Hardened Thick Flat Washer - Metric Sizes

What Is a Hardened Thick Flat Washer?

A hardened thick flat washer is a heat-treated washer of increased thickness and hardness, engineered to sit beneath high-strength bolts and nuts in structural connections. When a high-strength bolt is tightened to its full preload, the pressure under the head and nut is enormous. A standard mild-steel washer would indent, dish, or embed into the joint, allowing the bolt to relax and lose clamp force. A hardened thick washer resists this deformation, preserving a stable, flat bearing surface and holding the specified preload over the life of the joint.

Manufactured to DIN 6916 and the structural bolting standard EN 14399-6, hardened thick flat washers are a core part of preloaded structural bolting assemblies alongside high-strength bolts and nuts. They distribute the concentrated load over a larger, unyielding area, protect the connected steelwork from damage, and accommodate the radius under the bolt head. Used extensively in steel-frame construction, bridges, towers, and heavy machinery, they are essential wherever a bolted joint must be tensioned to a high, reliable preload and remain tight under load and vibration.

Key Features and Benefits

• Resists Indentation: Hardened material withstands high-strength bolt preload without dishing or embedding into the joint.
• Maintains Clamp Force: A stable, flat bearing surface preserves the specified preload over the joint's life.
• Distributes High Load: Spreads concentrated bolt force over a larger, unyielding area, protecting the steelwork.
• Structural Compliance: Manufactured to EN 14399-6 for use in certified preloaded structural bolting assemblies.
• Increased Thickness: Extra thickness accommodates the bolt head radius and resists deformation under tension.

Materials and Finishes

• Hardened Steel (Plain or Zinc): Heat-treated structural washers for high-strength bolted joints in general steelwork.
• Hot-Dip Galvanised: Heavy corrosion protection for exposed outdoor structural connections.
• Stainless Steel: Corrosion-resistant option where structural joints are exposed to aggressive environments.

Standards Compliance

• DIN 6916  Round washers for high-tensile structural bolting.
• EN 14399-6  Plain chamfered washers for preloaded structural bolting assemblies.
• DIN 7989  Thick washers for steel structures.

Size Range and Availability

Available in M12 through M36 in hardened steel, plain, zinc-plated, and hot-dip galvanised, matched to high-strength structural bolt assemblies.

Frequently Asked Questions (FAQs)

1. What is a hardened thick flat washer used for?

A hardened thick flat washer is used beneath high-strength bolts and nuts in structural joints to resist indentation, distribute high preload, and maintain clamp force common in steel construction, bridges, towers, and heavy machinery.

2. Why do structural bolts need hardened washers?

High-strength bolts generate enormous pressure under the head and nut at full preload. A standard washer would indent and let the bolt relax, so a hardened washer is needed to hold the bearing surface and preserve clamp force.

3. What is the difference between a hardened washer and a standard flat washer?

A hardened washer is heat-treated, thicker, and much harder, so it resists deformation under high-strength bolt preload. A standard flat washer is softer and would dish or embed under the same load.

4. What standards apply to hardened structural washers?

Hardened thick flat washers are made to DIN 6916 and the structural bolting standard EN 14399-6, and DIN 7989 covers thick washers for steel structures. These ensure the correct hardness and dimensions for preloaded joints.

5. Are hardened thick flat washers galvanised?

They are available plain, zinc-plated, and hot-dip galvanised. Galvanised versions provide heavy corrosion protection for exposed outdoor structural connections such as bridges and towers.

6. What size hardened washers do you stock?

We stock M12 through M36 hardened thick flat washers in plain, zinc-plated, and hot-dip galvanised finishes, matched to high-strength structural bolt assemblies.

7. Can I use a hardened washer with any bolt?

Hardened thick washers are designed for high-strength structural bolts and are used where high preload demands an indentation-resistant bearing surface. For general low-load joints a standard flat washer is usually sufficient.

8. What is a chamfered structural washer?

A chamfered washer, per EN 14399-6, has a chamfer on the inner edge to clear the radius under the bolt head, ensuring the washer sits flat against the steel. This is important for correct preload in structural joints.

9. Do hardened washers go under the head, the nut, or both?

In preloaded structural assemblies, a hardened washer is typically placed under the turned element (usually the nut), and sometimes under both, per the connection design. Always follow the structural bolting specification for the joint.

10. Are hardened thick flat washers reusable?

If undamaged and not deformed, they can be reused, but in certified preloaded structural connections the assembly components are often replaced as a set. Follow the applicable structural bolting procedure.