Our metric flanged bolts, manufactured to DIN 6921 and JIS B 1189, combine a hex head with an integrated flange that spreads clamping load over a wider area  eliminating the need for a separate washer. Serrated variants bite into the surface to resist loosening, making flange bolts a fast, secure choice for automotive, chassis, and machinery assembly.

Flanged Bolts - Metric Sizes

What Is a Flanged Bolt?

A flanged bolt  also called a hex flange bolt or frame bolt  is a hexagon-head fastener with a wide, integrated flange beneath the head that acts as a built-in washer. This flange distributes the clamping load across a larger bearing surface, reducing surface stress and the risk of the head pulling through soft or thin material. Because the washer function is built in, flanged bolts speed up assembly and remove the chance of a washer being dropped or omitted on the line.

Manufactured to DIN 6921 and EN 1665, flange bolts are widely specified in automotive, chassis, and high-volume machinery assembly. Serrated flange versions feature radial teeth on the underside that grip the mating surface, providing effective resistance to vibration-induced loosening without a separate lock washer. Smooth-flange versions are chosen where the mating surface must not be marred, such as on finished or coated panels.

Key Features and Benefits

• Integrated Washer Face: The wide flange spreads clamp load over a larger area, protecting soft and thin materials and speeding assembly.
• Serrated Anti-Loosening Grip: Radial serrations bite into the surface to resist vibration loosening without a separate lock washer.
• Faster Assembly: The built-in washer removes a component from the line, cutting handling time and preventing missing washers.
• Higher Bearing Strength: The flange reduces bearing stress and improves joint reliability under dynamic loads.
• Clean Smooth Option: Smooth-flange variants protect finished surfaces where serration marks are undesirable.

Materials and Finishes

• Carbon Steel Class 8.8 (Zinc Plated): General-purpose flange bolts for machinery and light chassis work.
• Alloy Steel Class 10.9: High-strength grade for automotive and structural joints.
• Stainless Steel A2 / A4: Corrosion-resistant flange bolts for outdoor and marine assemblies.

Standards Compliance

• DIN 6921  Hexagon flange bolts.
• EN 1665  Hexagon bolts with flange, heavy series.
• ISO 898-1  Mechanical property classes for steel bolts.
• JIS B 1189  JAPANESE INDUSTRIAL STANDARD 

Common Applications and Industries

Flange bolts are a staple of automotive and commercial vehicle assembly, securing chassis, suspension, engine ancillaries, and body components where fast, washer-free fixing speeds the production line. Serrated versions lock brackets, guards, and panels against the constant vibration of engines and road use. In general machinery, agricultural equipment, and steel fabrication they fasten frames, covers, and mounts, spreading load to protect thinner or softer materials.

Because the integrated flange removes a separate washer from the assembly sequence, flange bolts are favoured wherever high build volume and consistent quality matter, including appliance manufacture, HVAC plant, and structural bracketry. Smooth-flange versions serve finished or coated surfaces where serration marks would be unacceptable, such as visible panels and painted assemblies.

How to Choose the Right Flange Bolt

Decide first whether you need locking: serrated flange bolts grip the surface to resist vibration and suit unfinished, load-bearing joints, while smooth-flange versions protect finished surfaces but need a separate locking method under heavy vibration. Match the strength class to the load  Class 8.8 for general work and Class 10.9 for automotive and structural joints.

Consider the mating material: the wide flange is ideal for soft or thin components that a plain hex head would damage or pull through. Then choose the finish for the environment, from zinc-plated steel indoors to A2 or A4 stainless for corrosion resistance, and select a length that provides full thread engagement in the nut or tapped hole.

Size Range and Availability

Available in M5 through M20 in metric coarse thread, in serrated and smooth flange styles, across zinc-plated steel Class 8.8/10.9 and A2/A4 stainless.

Why Buy From Metric Specialties

As dedicated metric fastener specialists, we hold flanged bolts in the sizes, grades, and finishes that engineers actually need, backed by clear DIN and ISO standard references so you can specify with confidence. Every item is sourced to recognised standards and quality-controlled, giving you consistent thread fit, strength, and corrosion performance across repeat orders.

Whether you need a single item for a repair or bulk quantities for production, our range, technical guidance, and fast dispatch help you find the exact fastener for the job. If you are unsure which size, grade, or finish suits your application, our team can help you match the right product to your load, environment, and standard, so your assemblies are reliable and built to last.

Frequently Asked Questions (FAQs)

1. What is a flanged bolt used for?

Flanged bolts are used where a wide bearing surface and fast assembly are needed for automotive chassis, machinery frames, brackets, and thin or soft materials. The integrated flange replaces a separate washer.

2. What is the difference between a flange bolt and a standard hex bolt?

A flange bolt has a built-in flange beneath the head that acts as a washer, spreading load and speeding assembly. A standard hex bolt usually needs a separate washer to achieve the same bearing area.

3. What is a serrated flange bolt?

A serrated flange bolt has radial teeth on the underside of the flange that bite into the mating surface, resisting rotation and vibration loosening without needing a separate lock washer.

4. Do flanged bolts need a washer?

No, the integrated flange performs the washer's job of spreading clamp load, so a separate washer is not required. This is one of the main assembly-time advantages of flange bolts.

5. Do serrated flange bolts damage the surface?

The serrations leave small marks where they grip, which is intended for locking. For finished or coated surfaces that must stay unmarked, choose the smooth-flange version instead.

6. Are flange bolts good for vibration resistance?

Serrated flange bolts resist vibration-induced loosening well because their teeth grip the surface. For extreme vibration, combine correct torque with thread-locking adhesive.

7. Are flanged bolts available in stainless steel?

Yes. We stock A2 and A4 stainless flange bolts for corrosion-resistant applications such as marine, outdoor, and food-industry equipment.

8. What strength classes do flange bolts come in?

We stock Class 8.8 for general use and Class 10.9 for higher-strength automotive and structural joints, plus A2/A4 stainless grades.

9. What sizes do you stock for flanged bolts?

We stock M5 through M20 in metric coarse thread, in both serrated and smooth flange styles, across zinc-plated steel and A2/A4 stainless.

10. Can flange bolts be reused?

Smooth flange bolts can generally be reused if undamaged. Serrated flange bolts lose some grip once the teeth have deformed a surface, so replacement is advised for safety-critical joints.