Copper Washers: What They Are, How They Work & Why Mechanics Still Rely on Them
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Copper washers — often called copper crush washers — are some of the most reliable sealing components in automotive and hydraulic systems. They look simple, but they’re designed to create an extremely tight, leak-proof seal where metal fittings meet.
If you work with engines, fuel systems, braking systems, sump plugs or hydraulic lines, you’ve almost certainly used them. And if you’re replacing a fitting or banjo bolt, a fresh copper washer is not optional — it’s essential.
Here’s everything you need to know.
What Are Copper Washers?
Copper washers are flat rings made from soft, malleable copper.
Their flexibility is the key to their performance:
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When the washer is tightened between two metal surfaces,
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the copper compresses (“crushes”),
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filling micro-gaps,
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and creating a pressure-tight metal-to-metal seal.
This makes them ideal in systems with high pressure, vibration, or temperature changes.
Why Copper Washers Are Used
Copper has unique properties that make it one of the best sealing materials:
✔ Soft & compressible
Adapts perfectly to uneven metal surfaces.
✔ Excellent high-temperature resistance
Suitable for hot oil, fuel, coolant and hydraulic fluid.
✔ Strong corrosion resistance
Copper doesn’t rust — ideal for long-term reliability.
✔ Stable under pressure & vibration
Doesn’t deform or loosen easily.
✔ Recyclable & cost-effective
Works well and costs less than more complex gasket types.
This is why copper washers remain the standard in modern vehicles and machinery — despite newer materials being available.
Where Copper Washers Are Commonly Used
Copper sealing washers are essential in:
Automotive
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Brake line fittings
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ABS block connections
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Banjo bolts
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Turbo oil feeds/returns
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Sump plugs
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Fuel lines
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Power steering lines
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Injector leak-off fittings
Hydraulics
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Hydraulic pumps
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Pressure lines
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Valve blocks
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Industrial hydraulic systems
General Engineering
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Air compressors
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Machinery with metal-to-metal sealing
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Pneumatic systems
If a fitting carries oil, fuel or hydraulic fluid, there’s a good chance it uses a copper washer.
Are Copper Washers Reusable?
Technically… yes.
Practically… no.
Copper hardens after being crushed.
A used washer:
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won’t compress properly a second time,
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may not seal fully,
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and increases the risk of leaks.
Best practice:
Always fit a new copper washer during reassembly.
It’s not worth the cost of returning to a job because of a drip or pressure loss.
What About Annealed Copper Washers?
Annealing softens copper, returning it to a malleable state.
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Annealed = softer, better sealing
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Non-annealed = harder, less forgiving
At Seal With Selo, our copper washers are annealed, ensuring the best possible crush and seal performance.
Copper vs Bonded Washers (Rubber/Metal)
A quick comparison:
| Type | Best For | Avoid When |
|---|---|---|
| Copper Washer | High temps, oil/fuel lines, brake/hydraulic systems | Large surface irregularities |
| Bonded Washer | Lower torque applications, flat faces, coolant fittings | Extreme temperatures or pressure |
If you’re sealing oil, fuel, ATF or hydraulic fluid, copper remains the safest choice.
Choosing the Correct Size
The washer size must match:
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The bolt size (M6, M8, M10, M12, M14, etc.)
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The seat surface
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The application pressure
We stock all the common metric sizes, with no minimum quantity — ideal for both mechanics and DIY repairs.
Browse Copper Washers
Copper Washers – Metric & Imperial Sealing Washers | SealWithSelo – Seal with Selo
In Summary
Copper washers continue to be the most dependable sealing option for automotive and hydraulic systems. Their ability to deform, seal, and withstand heat makes them an essential part of every mechanic’s toolbox.
Whether you need one washer or a hundred, Seal With Selo has a full range of metric copper washers, dispatched fast and without minimum order rules.