Knowledge · EPDM
Pressure Washer O-Ring Size Guide: 5 Common Metric Sizes and Material Choices
Compare five commonly requested metric O-ring sizes for pressure washer repairs. Measure ID and CS first, then choose an available NBR or EPDM small pack. This is not a universal compatibility chart.
Pressure Washer O-Ring Size Guide: 5 Common Metric Sizes and Material Choices
A pressure washer leak at a quick connect, hose, spray gun, wand, coupler, or pump fitting does not automatically tell you which O-ring to buy. Labels such as 1/4 inch, 3/8 inch, and M22 usually describe the fitting context—not the O-ring inside diameter or cross section.
This guide compares five commonly requested metric sizes currently available through OxxRing small-pack products. It is a measured-size buying guide, not a universal pressure washer compatibility chart. Measure the original seal or groove before ordering.
Need help measuring? Use the O-Ring Size Guide or follow the detailed ID, OD, and cross-section measurement guide.
Fix the leak. Get the O-rings you need.
Know the exact size? Shop small packs by size. Need an assortment for maintenance? Explore the 990PC Pressure Washer & Air Seal Kit for hose, washer and workshop repair jobs.
Quick Size and Material Selection Table
| O-ring size (ID × CS) | Approx. OD | Inch reference | Available small-pack choices |
|---|---|---|---|
| 8.60 × 2.70 mm | 14.00 mm | 0.339 × 0.106 in | NBR 70A · EPDM 70A |
| 9.80 × 2.10 mm | 14.00 mm | 0.386 × 0.083 in | NBR 70A · EPDM 70A |
| 10.00 × 2.80 mm | 15.60 mm | 0.394 × 0.110 in | EPDM 70A |
| 12.70 × 2.65 mm | 18.00 mm | 0.500 × 0.104 in | NBR 70A · EPDM 70A |
| 9.00 × 3.00 mm | 15.00 mm | 0.354 × 0.118 in | NBR 70A |
Important: Two O-rings can have a similar outside diameter but different inside diameters and cross sections. For example, 8.60 × 2.70 mm and 9.80 × 2.10 mm both have an approximate 14.00 mm OD, but they are not interchangeable.
For a different measured metric ID × CS, browse the DIN / ISO metric O-ring listings to compare available sizes and materials. A listed size does not guarantee fit for any specific pressure washer.
How to Confirm the Size
1. Identify the exact leak location
Check whether the leak is at the quick-connect socket, plug side, hose end, spray-gun inlet, spray-gun outlet, wand joint, nozzle connection, or pump fitting. Different locations on the same pressure washer can use different seals.
2. Measure the inside diameter
Measure across the opening of the relaxed O-ring. Do not measure the outside edge and call it the ID.
3. Measure the cross section
Cross section is the thickness of the rubber ring. A small difference here can determine whether the fitting seals, will not assemble, or leaks under pressure.
4. Use outside diameter as a check
For a round O-ring:
OD = ID + 2 × CS
OD is useful as a confirmation value, but ID and CS should remain the primary ordering dimensions.
5. Do not trust a damaged ring alone
A stretched, flattened, swollen, torn, or hardened O-ring can give a misleading measurement. When the old seal is damaged or missing, inspect and measure the groove or fitting seat.
NBR or EPDM: Which Material Should You Choose?
Choose EPDM for mainly water and outdoor exposure
EPDM is commonly selected for water, weather, ozone, moisture, and outdoor service. It is often the more natural starting point for a water-only pressure washer connection that is exposed to outdoor conditions.
Do not use EPDM as a default where petroleum oil, grease, or fuel exposure is part of the service. Detergent and cleaner compatibility should also be reviewed rather than assumed.
Choose NBR when oil or grease resistance matters
NBR is widely used for general mechanical sealing and applications involving petroleum oils and greases. It may be considered around equipment areas where those exposures matter.
NBR is not automatically the best choice for every water-only or outdoor connection. Material selection should follow the actual fluid, cleaner, temperature, weather, and duty conditions.
For broader comparisons, see the O-Ring Material Guide. For unusual cleaners, heat, chemicals, or critical service, use Custom O-Ring Quote instead of guessing.
Five Sizes to Compare After Measuring
8.60 × 2.70 mm
This size has an 8.60 mm ID, 2.70 mm cross section, and approximately 14.00 mm OD. Current small-pack choices:
9.80 × 2.10 mm
This size has a 9.80 mm ID, 2.10 mm cross section, and approximately 14.00 mm OD. It is not interchangeable with 8.60 × 2.70 mm even though the calculated OD is the same.
10.00 × 2.80 mm
This size has a 10.00 mm ID, 2.80 mm cross section, and approximately 15.60 mm OD. Current direct-buy choice:
12.70 × 2.65 mm
This size has a 12.70 mm ID, 2.65 mm cross section, and approximately 18.00 mm OD. Current small-pack choices:
9.00 × 3.00 mm
This size has a 9.00 mm ID, 3.00 mm cross section, and approximately 15.00 mm OD. Current direct-buy choice:
What 1/4 Inch, 3/8 Inch, and M22 Do Not Tell You
These labels can help identify a connector family or repair location, but they do not confirm the O-ring ID, CS, material, hardness, or groove design. Do not choose one of the five products above only because the fitting is described as 1/4 inch, 3/8 inch, or M22.
A Safer Buying Path
- Release pressure and locate the exact leaking connection.
- Inspect the O-ring, groove, seat, and connector for damage.
- Measure ID and CS.
- Use OD only as a check value.
- Choose NBR or EPDM based on actual exposure.
- Compare the measured result with the five sizes above.
- Buy a small pack only when the dimensions and material are confirmed.
Browse Shop Small Packs when the size and material are known. Use Custom O-Ring Quote for an unknown size, missing sample, unusual material, drawing, larger quantity, or failed repair that needs further review.
FAQ
What is the most common pressure washer O-ring size?
There is no single universal size. Pressure washers use different seals across quick connects, hoses, guns, wands, adapters, and pump fittings. Measure the specific seal location before ordering.
Can two O-rings with the same outside diameter be different?
Yes. 8.60 × 2.70 mm and 9.80 × 2.10 mm both calculate to approximately 14.00 mm OD, but their ID and cross section are different. They should not be treated as substitutes.
Is EPDM always better for pressure washers?
No. EPDM is often considered for water and outdoor exposure, while NBR is often considered where petroleum oil or grease resistance matters. Cleaner, temperature, and mixed-media exposure must also be reviewed.
Can I order by pressure washer brand or model?
Not from this guide alone. A brand or model may help locate an OEM diagram, but OxxRing does not claim model-specific fit here. Confirm ID, CS, and material first.
What should I do if the old O-ring is missing?
Measure the groove and mating fitting, look for an OEM part diagram, or use Custom O-Ring Quote with clear photos and measurements. Do not choose only by appearance.
Find a matching replacement after measuring
For quick-connect, spray-gun, hose or pump-fitting repairs, measure the actual O-ring inside diameter (ID) and cross section (CS), then find catalog configurations by those dimensions. Confirm material, hardness and the equipment-specific seal requirement before ordering. The five sizes described here are examples, not universal pressure-washer fitment approvals.
Final Check Before Ordering
Confirm the leak location, ID, CS, approximate OD, material exposure, and connector condition. The five sizes in this guide provide a faster route after measurement; they do not replace measurement or equipment-specific verification.
