In any fastening system—whether in construction, automotive, electronics, or heavy machinery—washers play a critical yet often overlooked role. These simple components, placed between a fastener and the surface it secures, serve far more than just a supportive function. From distributing load and preventing surface damage to resisting loosening and isolating materials, washers are essential for ensuring mechanical integrity, longevity, and safety in joints.
Understanding what washers are, when and how to use them, and which type to choose based on the application is crucial for engineers, technicians, and DIY builders alike. In this guide, we’ll break down the core functions of washers, highlight their different types, and explain best practices for proper usage—so you can build smarter, stronger, and safer.
What Is a Washer?
A washer is a thin, typically round plate with a hole in the center, used in conjunction with bolts, screws, or nuts. Washers are placed between the fastener and the surface of the material to:
- Distribute load
- Prevent surface damage
- Enhance clamping stability
- Reduce loosening due to vibration
- Isolate materials to prevent corrosion
Main Types of Washers
| Type | Description | Common Use Cases |
| Flat Washer | Distributes load evenly. | General use, soft or coated surfaces |
| Spring Washer | Applies axial load to resist loosening. | Vibrating machines, moving parts |
| Lock Washer | Prevents rotation of bolt or nut. | Automotive, mechanical assemblies |
| Fender Washer | Large OD, thin washer for wide load distribution. | Sheet metal, oversized holes |
| Countersunk Washer | Fits under countersunk heads for flush surfaces. | Furniture, decorative applications |
| Sealing Washer | Includes rubber or elastomer for watertight sealing. | Plumbing, electrical enclosures |
| Shoulder Washer | Electrically insulates fastener from base material. | Electronics, circuit boards |
| Split Washer | A common lock washer, slightly twisted to apply tension. | Prevents loosening under dynamic loads |
| Toothed Washer | Has internal or external teeth for improved grip. | Electrical connections, grounding systems |
Where Should Washers Be Used
1. Under Bolt or Screw Heads
- Purpose: To distribute the load over a larger surface area and prevent surface damage.
- Use case: On softer materials (wood, plastic, aluminum), or when tightening to a painted or plated surface.
2. Under Nuts
- Purpose: Prevents the nut from digging into the surface and helps maintain preload.
- Use case: Critical bolted joints, machinery, automotive parts.
3. With Soft or Brittle Materials
- Purpose: Avoids cracking, deformation, or crushing of the base material.
- Use case: Wood, glass-reinforced plastic, composite panels.
4. To Prevent Loosening
- Purpose: Spring washers, lock washers, or serrated washers help resist vibration-induced loosening.
- Use case: Engines, motors, vehicles, vibrating machinery.
5. For Corrosion Isolation
- Purpose: Use insulating washers to separate dissimilar metals and prevent galvanic corrosion.
- Use case: Stainless steel bolts in aluminum frames, marine environments.
6. When Spacing or Alignment is Needed
- Purpose: Flat washers can be stacked or precision washers used to adjust height or alignment.
- Use case: Gear assemblies, electrical enclosures, equipment mounts.
7. When Using Oversized Holes
- Purpose: Washers provide a proper bearing surface when holes are slotted or larger than the fastener.
- Use case: Structural steelwork, adjustable mounts, repair work.
When NOT to Use Washers
- Direct torque transfer is required (e.g., flange bolts with serrated faces).
- Thread engagement is too short, and washer thickness may reduce clamping force.
- Space or weight constraints in critical aerospace or precision instruments.
How to Use Washers
1 Placement
- Insert the washer between the bolt or nut and the surface of the workpiece.
- If both sides need protection, use washers under both the bolt head and the nut.
2 Proper Fit
- Choose a washer with an inner diameter slightly larger than the fastener’s thread diameter.
- Outer diameter should be wide enough to spread the load without interfering with other components.
3 Torque Consideration
- Adjust tightening torque as washers (especially spring or lock types) can affect friction and preload.
FAQ: Where Should Washers Be Used?
Not always, but washers are recommended in many cases—especially when working with soft materials (like wood or plastic), large holes, or where vibration is present.
Flat washers should be used when:
- You want to spread the load to prevent surface damage.
- The material is soft or painted.
- The hole is slightly oversized or irregular.
Not strictly, but adding a flat washer can still help protect the surface and distribute the load. In high-vibration applications, lock washers may also be added.
Yes, in some cases. Especially when:
Both surfaces need protection.
Load distribution is important on both ends.
You are working with thin or fragile materials.
Use them when:
Fasteners are subject to vibration or dynamic loads.
There's a risk of loosening over time.
In machinery, vehicles, or industrial equipment.
Generally no. Wood screws are designed to create a strong grip without a washer. However, a washer might be used if:
You’re attaching something delicate on top.
The wood is soft and prone to damage.
Yes, especially flat washers. They:
Protect metal surfaces.
Prevent galling and wear.
Allow for smoother torque application.
Yes. Use shoulder or insulating washers when:
Preventing electrical conductivity is essential.
You need to isolate the fastener from circuit boards or housings.
Contact MT.BOLTS
MT.BOLTS specializes in the manufacturing and supply of Steel Fasteners, including screws, bolts, nuts, and washers. Our products conform to international standards (ANSI / ASTM / DIN / ISO / JIS) and are available in various materials, dimensions, and surface finishes.
Contact us today to learn more about fasteners and to procure high-quality products. Our technical team is ready to provide expert support and custom selection solutions.
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