Flat Washers

Flat Washers for Structural & Slotted Holes

Heavy-Duty Load Distribution for Structural Assemblies

Manufacturer & Exporter: Super Industries India

1. Why ISO 7091 Exists (Flat Washers)

ISO 7091 washers are engineered specifically for:

• Structural steel joints
• Slotted or oversized holes
• High clamping forces

They differ from ISO 7089 and ISO 7090 by combining:

• Larger outside diameter
• Increased thickness
• Higher stiffness

This makes ISO 7091 washers essential in load-critical joints.

2. ISO 7091 vs ISO 7089 vs ISO 7090 (Engineer Decision Matrix)

Parameter	ISO 7089	ISO 7090	ISO 7091
OD size	Normal	Large	Large (structural)
Thickness	Normal	Normal	Thick
Slotted holes	❌	⚠️	✔
Structural use	❌	⚠️	✔✔

3. Primary Functions in Structural Joints

ISO 7091 washers:

• Bridge elongated holes
• Prevent localized crushing
• Stabilize clamp force
• Improve fatigue resistance

They are not optional in structural bolting systems.

4. Typical Applications

• Steel structures
• Bridges
• Power plants
• Wind towers
• Pipe racks
• Heavy machinery frames

5. Dimensional Characteristics

• Inner diameter: Standard bolt clearance
• Outer diameter: Enlarged
• Thickness: Increased to resist bending

Common sizes:
M10 to M36 (larger on request)

6. Load Behavior Under High Preload

Structural washers must:

• Remain flat
• Resist cupping
• Maintain preload under cyclic load

ISO 7091 washers achieve this through increased section modulus.

7. Washer Hardness Requirements

Bolt Grade	Washer Requirement
8.8	Hardened recommended
10.9	Hardened mandatory
12.9	Structural washer only

Super Industries India supplies 300 HV washers as standard for ISO 7091.

8. Material Options

• Carbon steel
• Alloy steel
• Stainless steel (limited structural use)
• Project-specific grades

9. Surface Finishes

• Black / oiled
• Hot dip galvanized (structural norm)
• Zinc plated (indoor structural)
• Special coatings on request

10. Compatibility with Structural Bolts

ISO 7091 washers are commonly paired with:

• ISO 4014 bolts
• ISO 4017 bolts (non-shear)
• ISO 4032 nuts
• ISO 898-1 high-strength bolts

11. Manufacturing Controls

• Precision blanking
• Controlled heat treatment
• Flatness verification
• Coating after inspection

12. Inspection Criteria

• Thickness tolerance
• Flatness
• Hardness testing
• Coating thickness
• Visual inspection for edge defects

13. Common Engineering Errors

❌ Using thin washers in slotted holes
❌ Mixing washer hardness with high-grade bolts
❌ Skipping washers in structural joints

14. Export & Project Supply

Super Industries India supplies ISO 7091 washers for:

• EPC contracts
• Infrastructure projects
• Steel fabrication yards

With:
✔ Mill test certificates
✔ Batch traceability
✔ Export packing

15. Custom ISO 7091 Washers

• Non-standard OD/thickness
• Heavy-duty variants
• Project coatings
• Special marking

16. Buyer FAQ

Q: Are ISO 7091 washers mandatory for slotted holes?
Yes, they are strongly recommended in structural applications.

Q: Can ISO 7090 replace ISO 7091?
No. ISO 7090 lacks structural thickness.

17. When ISO 7091 Is Required

Use ISO 7091 when:
✔ Holes are slotted or oversized
✔ Loads are structural
✔ Bolt grade ≥ 10.9
✔ Fatigue resistance is required

18. Conclusion

ISO 7091 washers are structural components, not accessories.
They protect joints, stabilize preload, and ensure long-term integrity.

Super Industries India supplies ISO 7091 washers engineered for critical structural applications worldwide.