JASO F404 is the Japanese automotive standard for metric O-ring dimensions, published by the Society of Automotive Engineers of Japan (JASO). It defines inside diameters and cross sections used in fuel injection, engine oil, cooling, power steering, air conditioning, and other vehicle sealing systems. The standard is widely used by Japanese domestic vehicle manufacturers, Tier-1 suppliers, motorcycle producers, and automotive supply chains across Southeast Asia.
This guide covers the JASO F404 size system, cross-section series, tolerances, groove design, automotive materials, and how the standard relates to ISO 3601 and AS568. See the JASO F404 standard page for the full size chart.
Short Answer: JASO F404 at a Glance
| Attribute | JASO F404 |
|---|---|
| Publisher | Society of Automotive Engineers of Japan (JASO) |
| Unit system | Metric (millimetres) |
| Size notation | Inside diameter × cross section, e.g. 7.50 × 1.90 mm |
| Primary cross sections | 1.50 mm to 5.70 mm |
| Automotive focus | Fuel, oil, coolant, A/C, power steering, brake, transmission |
| Closest Japanese standard | JIS B 2401 P-series and G-series |
| International overlap | ISO 3601 A/B/C/D-series, AS568 metric conversions |
A complete JASO F404 specification includes ID × CS in millimetres, material (FKM, HNBR, NBR, etc.), hardness (Shore A), and the automotive tolerance band.
What Is JASO F404?
JASO F404 is a dimensional standard, not a material specification. It catalogues metric O-ring inside diameters and cross-sectional diameters standardized for passenger cars, motorcycles, commercial vehicles, and small engines. The standard is closely aligned with JIS B 2401 and broadly compatible with ISO 3601 metric sizes.
Key facts:
- Dimensions are metric.
- Tolerances are tighter than general-purpose industrial O-rings but not as tight as aerospace Class 2 tolerances.
- Material selection is left to the engineer and is usually governed by OEM specifications, ASTM D2000 line calls, or JASO material test requirements.
Automotive Applications
JASO F404 sizes appear throughout Japanese vehicles and global platforms that source from Japanese suppliers:
- Fuel injection — rail fittings, injector seals, pressure regulators, quick connectors.
- Engine oil — oil pans, oil filter housings, cooler lines, valve covers.
- Cooling systems — water pumps, thermostat housings, radiator tanks, coolant passages.
- Power steering — pump housings, rack-and-pinion seals, reservoir caps.
- Air conditioning — compressor ports, refrigerant lines, expansion valves.
- Brake systems — master cylinders, wheel cylinders, ABS modulators.
- Transmissions — valve bodies, clutch pistons, transfer cases.
See the automotive industry page for recommended materials and failure-mode analysis.
Cross-Section Series
JASO F404 covers cross sections from miniature 1.50 mm seals up to 5.70 mm large vacuum seals. Many sizes intentionally match ISO 3601 A/B/C/D-series or AS568 metric equivalents so suppliers can use common tooling.
| CS (mm) | Automotive Application / Note |
|---|---|
| 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 |
The 1.90 mm cross section is the signature JASO F404 size for fuel-system seals, offering slightly more compression and tolerance absorption than the 1.80 mm ISO A-series.
Dimensional Tolerances
Tolerances are grouped by cross-section range and inside-diameter range. Both must be verified because automotive glands are machined to tight groove widths and depths.
| CS (mm) | CS Tolerance | ID Range (mm) | 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 |
For a 7.50 × 1.90 mm seal, the cross-section tolerance is ±0.09 mm and the inside-diameter tolerance is ±0.17 mm. The ID tolerance band widens with diameter because larger moulded rings are harder to hold to tight absolute limits while still meeting gland design requirements.
Groove Design
JASO F404 follows the same gland design principles as JIS B 2401 and ISO 3601. Groove width and depth depend on the service type.
| Service Type | Groove Width Guidance | Compression / Fill Guidance |
|---|---|---|
| Static | ≈ 1.15 × CS | 15 – 22 % compression for face and radial static seals |
| Dynamic (reciprocating) | ≈ 1.2 – 1.3 × CS | 10 – 15 % compression for fuel injector and coolant dynamic seals |
| Rotary | Limit groove fill to 75 – 80 % maximum | Use FKM or HNBR; avoid NBR for high-speed rotary service |
Squeeze calculation: Squeeze (%) = (CS − Groove Depth) / CS × 100. A 1.90 mm CS seal in a 1.65 mm dynamic groove gives (1.90 − 1.65) / 1.90 × 100 = 13.2 %, within the recommended dynamic range.
Use our O-ring compression calculator to verify squeeze percentage and gland fill for any JASO F404 size.
JASO F404 vs ISO 3601 and AS568
JASO F404 is Japanese automotive, ISO 3601 is international metric, and AS568 is North American inch-based. They are not identical, but global automotive supply chains require interchangeable sourcing.
| Standard | Region / Body | Size Basis | Relationship to JASO F404 |
|---|---|---|---|
| JIS B 2401 | Japan / JIS | Metric | P-series and G-series align directly with JASO F404 automotive sizes |
| ISO 3601 | International / ISO | Metric | A/B/C/D-series cross sections are compatible with JASO F404 |
| DIN 3771 | Germany / EU | Metric | German metric sizes overlap with JASO F404 for automotive hydraulics |
| AS568 | USA / SAE | Inch | Imperial cross sections convert to nearest metric JASO sizes |
| SMS 1588 | Sweden / SMS | Metric | Swedish metric sizes share common cross sections with JASO F404 |
Practical guidance:
- A 7.50 × 1.90 mm JASO seal is not interchangeable with a 7.50 × 1.80 mm ISO seal; the 0.10 mm CS difference changes gland fill and compression.
- JASO F404 1.80 mm, 2.65 mm, 3.55 mm, and 5.30 mm cross sections match ISO 3601 A, B, C, and D-series respectively.
- AS568 cross sections convert cleanly: 0.070 in = 1.78 mm, 0.103 in = 2.62 mm, 0.139 in = 3.53 mm, 0.210 in = 5.33 mm.
Many OEMs specify a JASO F404 primary size and an ISO 3601 secondary source, with a drawing tolerance that both must meet.
Common Size Examples
Representative JASO F404 sizes used in automotive subsystems. OD = ID + 2 × CS.
| ID (mm) | CS (mm) | OD (mm) | Typical Automotive Use |
|---|---|---|---|
| 4.00 | 1.50 | 7.00 | Small fuel injectors |
| 6.00 | 1.80 | 9.60 | Fuel system connectors |
| 7.50 | 1.90 | 11.30 | JASO F404 primary fuel seal size |
| 8.00 | 2.00 | 12.00 | Coolant fittings |
| 10.00 | 2.40 | 14.80 | Oil filter housings |
| 11.00 | 2.50 | 16.00 | A/C refrigerant lines |
| 12.00 | 2.65 | 17.30 | Power steering pumps |
| 14.00 | 3.00 | 20.00 | Transmission housings |
| 16.00 | 3.10 | 22.20 | Engine coolant passages |
| 18.00 | 3.50 | 25.00 | Large fuel system flanges |
| 20.00 | 3.55 | 27.10 | Heavy-duty engine seals |
| 25.00 | 4.00 | 33.00 | Commercial vehicle hydraulics |
| 30.00 | 5.00 | 40.00 | Truck air brake systems |
| 35.00 | 5.30 | 45.60 | Large automotive static seals |
| 40.00 | 5.70 | 51.40 | JIS V-series large vacuum seals |
Always confirm the exact ID × CS, material, hardness, and tolerance band from the drawing before ordering.
Material Selection for Automotive
JASO F404 defines dimensions only; the engineer must select the elastomer. Automotive fluid compatibility and temperature dominate the decision.
| Material | Hardness (typical) | Automotive Suitability | Common JASO F404 Use |
|---|---|---|---|
| NBR (Nitrile) | 70 – 90 Shore A | Petroleum fuels, mineral oils, greases | General fuel and oil seals, low-cost replacements |
| HNBR | 70 – 90 Shore A | Sour gasoline, biofuels, ozone, elevated temperature | Fuel injectors, timing covers, turbo oil lines |
| FKM (Viton®) | 75 – 90 Shore A | Aromatic fuels, high heat, engine oil | Fuel rails, direct-injection seals, A/C compressor seals |
| EPDM | 70 – 80 Shore A | Coolant, water, steam, brake fluid | Coolant passages, water pumps, brake reservoirs |
| VMQ (Silicone) | 60 – 70 Shore A | Wide temperature range, low-temp flexibility | Cold-climate seals, sensors, emissions equipment |
| AFLAS® | 75 – 90 Shore A | Amine-containing fluids, high-temperature oil | Transmission oil, some electric-vehicle coolants |
FKM and HNBR are the defaults for modern fuel systems. NBR remains common for non-critical oil and fuel seals. EPDM must never be used in fuel or oil service because it will swell and fail.
Inspection and Acceptance
JASO F404 O-rings should be inspected to dimensional and visual criteria consistent with automotive quality expectations. Most suppliers also support IATF 16949 controls and PPAP documentation.
Dimensional inspection:
- Inside diameter measured with optical comparator, cone gauge, or non-contact video system.
- Cross section measured at three points around the circumference.
- Both dimensions must fall within the applicable tolerance band.
Visual inspection:
- No porosity, blisters, voids, cracks, tears, or cuts visible at the surface.
- No foreign inclusions or contamination.
- Parting-line flash within the agreed automotive limit.
- Flow lines and mould marks acceptable if they do not exceed flash-height limits.
Batch testing (when required):
- Hardness per ASTM D2240 / JIS K 6253.
- Tensile strength and elongation per ASTM D412 / JIS K 6251.
- Compression set per ASTM D395 Method B / JIS K 6262.
- Fluid swell per ASTM D471 / JIS K 6258 for the relevant automotive fluid.
FAQ
Q1: What is JASO F404 and who publishes it?
JASO F404 is a Japanese automotive standard for metric O-ring dimensions, published by the Society of Automotive Engineers of Japan (JASO). It covers inside diameters, cross sections, tolerances, and recommended automotive applications, but not materials or compounds.
Q2: How does JASO F404 differ from JIS B 2401?
JASO F404 is automotive-specific and published by JASO. JIS B 2401 is the broader Japanese industrial standard. Most JASO F404 sizes come from JIS B 2401 P-series and G-series, but JASO F404 uses tighter automotive tolerances and is referenced directly in OEM drawings.
Q3: Are JASO F404 O-rings interchangeable with ISO 3601 sizes?
Often yes, but not automatically. JASO 1.80 mm matches ISO A-series, 2.65 mm matches B-series, 3.55 mm matches C-series, and 5.30 mm matches D-series. Some sizes such as 7.50 × 1.90 mm do not have an exact ISO counterpart. Always verify gland fill and compression before substituting.
Q4: How do JASO F404 sizes relate to AS568 dash numbers?
AS568 is inch-based. Its cross sections convert to metric values that appear in JASO F404: 0.070 in ≈ 1.78 mm, 0.103 in ≈ 2.62 mm, 0.139 in ≈ 3.53 mm, and 0.210 in ≈ 5.33 mm. AS568 uses dash numbers; JASO F404 uses ID × CS in millimetres.
Q5: What is the best material for JASO F404 fuel system O-rings?
FKM is the standard for gasoline and diesel fuel systems because of aromatic fuel resistance and high-temperature performance. HNBR is preferred for biofuels, sour gasoline, and low-temperature flexibility. NBR works for non-critical fuel and oil seals where cost matters.
Q6: What groove compression should be used for JASO F404 seals?
Static seals: 15 – 22 % compression. Dynamic reciprocating seals: 10 – 15 % compression to minimise friction and heat. Rotary seals: limit groove fill to 75 – 80 % maximum and use FKM or HNBR.
Q7: Are JASO F404 O-rings used outside Japan?
Yes. Global Tier-1 and Tier-2 suppliers use JASO F404 dimensions for vehicles exported from Japan, motorcycles, small engines, and any supply chain serving Japanese OEMs.
Q8: 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.
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Need JASO F404 O-rings for your automotive program? Request a quote with the ID × CS, material, hardness, quantity, and certification level. We can cross-reference JASO F404 to ISO 3601, AS568, or a custom drawing, and supply standard metric sizes from stock with full material traceability. For engineering support, contact our sealing team.