JASO F404 O-Ring Standard
Japanese automotive metric O-ring sizes for fuel, oil, coolant and air conditioning systems.
JASO F404 is the Japanese automotive standard for O-ring dimensions, published by the Society of Automotive Engineers of Japan. It is widely used in Japanese domestic vehicles (JDM), global automotive supply chains, and motorcycle manufacturing. The standard defines metric inside diameters and cross sections specifically for fuel injection systems, engine oil circuits, cooling systems, power steering, and automotive air conditioning. JASO F404 sizes are closely aligned with JIS B 2401 P-series and ISO 3601 A/B-series, making them compatible with most Asian and European automotive sealing specifications.
Cross Sections
| Cross Section (mm) | Notes |
|---|---|
| 1.50 | Small fuel injectors, sensors, miniature fittings |
| 1.60 | Compact automotive connectors |
| 1.78 | Compatible with AS568-004 cross section |
| 1.80 | Equivalent to JIS B 2401 P-series and ISO 3601 A-series |
| 1.90 | JASO F404 primary cross section for fuel system seals |
| 2.00 | Coolant and power steering fittings |
| 2.40 | Medium-pressure oil and transmission circuits |
| 2.50 | Air conditioning and refrigerant lines |
| 2.62 | Compatible with AS568-1xx cross section |
| 2.65 | Equivalent to JIS B 2401 G-series and ISO 3601 B-series |
| 3.00 | Heavy-duty engine and transmission seals |
| 3.10 | Common in JIS B 2401 P-series large sizes |
| 3.50 | JIS B 2401 P-series large diameter seals |
| 3.53 | Compatible with AS568-2xx cross section |
| 3.55 | Equivalent to ISO 3601 C-series |
| 4.00 | Large bore automotive static seals |
| 5.00 | Heavy equipment and commercial vehicle hydraulics |
| 5.30 | Equivalent to ISO 3601 D-series |
| 5.33 | Compatible with AS568-3xx cross section |
| 5.70 | JIS B 2401 V-series vacuum and large static seals |
Tolerances
| Cross Section (mm) | CS Tolerance | ID Range | ID Tolerance |
|---|---|---|---|
| 1.50 - 1.80 | ±0.08 | ≤ 10 | ±0.14 |
| 1.50 - 1.80 | ±0.08 | 10 - 20 | ±0.17 |
| 1.90 - 2.65 | ±0.09 | ≤ 13 | ±0.17 |
| 1.90 - 2.65 | ±0.09 | 13 - 30 | ±0.22 |
| 1.90 - 2.65 | ±0.09 | 30 - 50 | ±0.28 |
| 3.00 - 3.55 | ±0.10 | ≤ 20 | ±0.20 |
| 3.00 - 3.55 | ±0.10 | 20 - 40 | ±0.28 |
| 3.00 - 3.55 | ±0.10 | 40 - 85 | ±0.36 |
| 4.00 - 5.33 | ±0.13 | ≤ 40 | ±0.28 |
| 4.00 - 5.33 | ±0.13 | 40 - 80 | ±0.36 |
| 4.00 - 5.33 | ±0.13 | 80 - 140 | ±0.45 |
| 5.70 | ±0.15 | ≤ 80 | ±0.36 |
| 5.70 | ±0.15 | 80 - 160 | ±0.45 |
Common Size Examples
| Inside Diameter (mm) | Cross Section (mm) | Application |
|---|---|---|
| 4.00 | 1.50 | Small fuel injectors |
| 6.00 | 1.80 | Fuel system connectors |
| 7.50 | 1.90 | JASO F404 primary fuel seal size |
| 8.00 | 2.00 | Coolant fittings |
| 10.00 | 2.40 | Oil filter housings |
| 11.00 | 2.50 | A/C refrigerant lines |
| 12.00 | 2.65 | Power steering pumps |
| 14.00 | 3.00 | Transmission housings |
| 16.00 | 3.10 | Engine coolant passages |
| 18.00 | 3.50 | Large fuel system flanges |
| 20.00 | 3.55 | Heavy-duty engine seals |
| 25.00 | 4.00 | Commercial vehicle hydraulics |
| 30.00 | 5.00 | Truck air brake systems |
| 35.00 | 5.30 | Large automotive static seals |
| 40.00 | 5.70 | JIS V-series large vacuum seals |
Cross Reference to Other Standards
| Standard | Region | Designation Notes |
|---|---|---|
| JIS B 2401 | Japan | P-series and G-series align directly with JASO F404 automotive sizes |
| ISO 3601 | International | A/B/C/D series cross sections are compatible with JASO F404 |
| DIN 3771 | Germany/EU | German metric sizes overlap with JASO F404 for automotive hydraulics |
| AS568 | USA | Imperial cross sections convert to nearest metric JASO sizes |
| SMS 1588 | Sweden | Swedish metric sizes share common cross sections with JASO F404 |
Groove Design Guidelines
Static Seals
Groove width ≈ 1.15 × CS with 15-22% compression for automotive face and radial static seals.
Dynamic Seals
Groove width ≈ 1.2-1.3 × CS. Target 10-15% compression for fuel injector and coolant dynamic seals to minimise friction and heat.
Rotary Seals
Limit groove fill to 75-80% max. Use FKM or HNBR for engine accessory drives. Avoid NBR for high-speed rotary service.
JASO F404 FAQ
What is the difference between JASO F404 and JIS B 2401?
JASO F404 is specifically for automotive applications and published by the Society of Automotive Engineers of Japan. JIS B 2401 is the broader Japanese industrial standard. Most JASO F404 sizes are drawn from JIS B 2401 P-series and G-series, but with tighter automotive-specific tolerances and material requirements.
What is the best material for JASO F404 fuel system O-rings?
FKM (Viton) is the standard for gasoline and diesel fuel systems due to its excellent aromatic fuel resistance. HNBR is preferred for bio-fuels, sour gasoline, and when low-temperature flexibility is required.
Are JASO F404 O-rings used outside Japan?
Yes. Many global Tier-1 and Tier-2 automotive suppliers use JASO F404 dimensions for vehicles exported from Japan, as well as for motorcycles and small engines manufactured in Southeast Asia.
Can you supply JASO F404 O-rings to automotive PPAP and IATF 16949 requirements?
Yes. We can support PPAP documentation, material test reports, and IATF 16949 manufacturing controls for JASO F404 automotive O-ring programs.
Need JASO F404 O-rings?
Request a quote for Japanese automotive standard O-rings. Custom sizes and automotive certifications available.
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