Don’t Underestimate Washers｜The Unsung Heroes of Screw Fastening

In machines and structures, washers are the most common yet most overlooked small parts. Placed between the screw/nut and the mating surface, they spread load, prevent loosening, and protect surfaces from damage.

The two most universal types are Flat Washers and Spring Washers:

• Flat Washer → Distributes the load from the screw or nut, prevents scratching of the mounting surface, and increases contact area.

• Spring Washer → Elastic design maintains tension and prevents loosening due to vibration.

These two are often used together: the flat washer protects the surface, while the spring washer provides anti-loosening—the most common pairing in many joints.

Thin as they are, using washers correctly can greatly improve the reliability of bolted joints.

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How to Choose the Right Washer

Select based on screw size and application environment:

• ID vs. Screw Shank → The inner diameter (ID) should be slightly larger than the screw’s diameter to slip on smoothly.

• OD (Outer Diameter) → Larger OD spreads load over a wider area.

• Thickness → Thicker washers increase load capacity, but excessive thickness can reduce available thread engagement.

Material options:

• Carbon Steel – Cost-effective, for general structures

• Stainless SUS304 – Good corrosion resistance; common for indoor/food equipment

• Stainless SUS316 – Superior corrosion resistance; ideal outdoors, coastal, or high-humidity areas

• Brass – Good conductivity; common in electrical parts or decorative uses

• PEEK – High-performance polymer; high temperature & chemical resistance for advanced equipment

• POM (Acetal/Delrin) – Lightweight, wear-resistant; good for electronics and precision parts

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Installation Notes

1. Confirm size – ID should fit the screw snugly, not loosely.

2. Placement – Typically under the nut or screw head; contact surface must be flat.

3. Combine wisely – Pair spring/lock washers with flat washers to enhance anti-loosening.

4. Avoid stacking – Don’t stack multiple washers unless shimming is part of the design.

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Common Use Cases

Machine assembly → Improves load distribution of bolted joints

• Automotive & motorcycle → Vibration damping and anti-loosening

• Construction & equipment installation → Protects structural surfaces

• Electronics → Insulating spacers or gap shims

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Washer Type Comparison

Type	Function	Typical Applications
Flat Washer	Distributes load; protects surfaces	General screw fastening
Spring Washer (Split/Lock Washer)	Provides elastic tension; anti-loosening under vibration	Machinery, automotive parts
Wave Washer	Elastic compensation; absorbs vibration & takes up play	Bearings, precision assemblies
Conical Washer (Belleville)	Conical spring action increases preload & load capacity	High-strength bolts; sustained clamping
Double Washer	Two-layer structure increases anti-loosening & elasticity	High-vibration environments
Internal Tooth Washer (Star, Internal)	Teeth bite the screw shank to resist rotation	Tight bore, hidden-tooth use cases
External Tooth Washer (Star, External)	Teeth bite the mating surface to resist loosening	When large-area anti-loosening is needed

Washer

In short:

• Need stability & surface protection → choose Flat Washer

• Need anti-loosening → choose Spring/Lock, Internal-tooth, or External-tooth washers

• Need shock absorption/compensation → choose Wave or Conical (Belleville) washers

• Need stronger anti-loosening in high vibration → choose Double Washer

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Picking by Requirement

• Distribute load, protect surfaces → Flat Washer

• Worried about loosening → Spring/Lock, Internal-tooth, or External-tooth

• Compensate installation tolerance → Wave or Conical (Belleville)

• High-vibration environments → Double Washer

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Why Choose Sheng Fong Precision?

When choosing washers, stable quality and broad specifications matter just as much:

• Materials – Carbon steel, stainless steels, and special anti-rust finishes

• Complete lineup – Flat, spring (lock), conical (Belleville), wave, etc.

• Strict inspection – Precise thickness and ID/OD for reliable installation

• Fast supply – Ample stock, supports small-lot and diverse needs

• Professional support – We recommend the best washer for your application

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📩 Contact us for washer selection advice on LINE (ID: @s9000)

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