JIS B 2401 Metric O-Ring Standard
Japan’s metric sizing system for O-rings, widely used in Asian machinery, automotive, and hydraulic equipment.
JIS B 2401 is the Japanese Industrial Standard for metric O-ring dimensions, used extensively in machinery manufactured in Japan and across Asia. The standard organizes sizes by inside diameter (ID) and cross-section (CS) in millimeters, similar to ISO 3601, but with slightly different ID increments and series definitions. The standard defines three primary cross-section series: - P Series (for fixed applications): 1.9mm, 2.4mm, 3.1mm, 3.5mm, 5.7mm, and 8.4mm cross-sections - G Series (for motion applications): 1.9mm, 2.4mm, 3.1mm, 3.5mm, 5.7mm, and 8.4mm cross-sections with different groove dimensions - V Series (for vacuum flanges): standardized sizes for vacuum equipment and semiconductor processing JIS B 2401 is dimensionally close to ISO 3601 and DIN 3771 for many common sizes, making interchangeability practical in general industrial applications. However, in precision assemblies—particularly in Japanese automotive and hydraulic OEM equipment—designing to the exact JIS specification ensures optimal fit and sealing performance.
JIS B 2401 Series Overview
| Series | Cross Section (mm) | Application |
|---|---|---|
| P | 1.9 | Static seals, flanges, covers, general fixed applications |
| P | 2.4 | Static seals, medium-duty industrial equipment |
| P | 3.1 | Static seals, heavy machinery, process equipment |
| P | 3.5 | Static seals, large diameter flanges and housings |
| P | 5.7 | Static seals, construction equipment, shipbuilding |
| P | 8.4 | Static seals, very large diameter applications |
| G | 1.9 | Dynamic seals, hydraulic cylinders, pneumatic actuators |
| G | 2.4 | Dynamic seals, general motion applications |
| G | 3.1 | Dynamic seals, heavy-duty hydraulic systems |
| G | 3.5 | Dynamic seals, large bore cylinders |
| G | 5.7 | Dynamic seals, construction and mining equipment |
| G | 8.4 | Dynamic seals, very large motion applications |
| V | 3.5 | Vacuum flanges, semiconductor processing equipment |
| V | 5.7 | Vacuum systems, large chamber seals |
Tolerances
| Cross Section (mm) | CS Tolerance | ID Range | ID Tolerance |
|---|---|---|---|
| 1.9 | ±0.08 | Up to 30 mm | ±0.14 |
| 2.4 | ±0.08 | 30–50 mm | ±0.17 |
| 3.1 | ±0.10 | 50–80 mm | ±0.21 |
| 3.5 | ±0.10 | 80–120 mm | ±0.26 |
| 5.7 | ±0.13 | 120–180 mm | ±0.32 |
| 8.4 | ±0.15 | Above 180 mm | ±0.40 |
Cross Reference to Other Standards
| Standard | Region | Designation Notes |
|---|---|---|
| JIS B 2401 | Japan / Asia | P / G / V series by ID x CS |
| ISO 3601 | International | Dimensionally similar; ID increments may differ slightly |
| DIN 3771 | Germany | Metric sizes aligned with ISO 3601 |
| AS568 | North America | Inch-based dash numbers; cross-reference available for common sizes |
Groove Design Guidelines
Static Seals
Squeeze 15–20%, groove width 1.15–1.25 x CS, edge radius minimum 0.1 mm
Dynamic Seals
Squeeze 8–15%, groove width 1.20–1.30 x CS, lead-in chamfer 15–20°
Vacuum Seals
Squeeze 18–25%, groove width 1.10–1.20 x CS, high surface finish Ra 0.4 μm
Browse JIS B 2401 Sizes
The JIS B 2401 standard defines over 660 individual O-ring sizes. Select a common size below or contact us for specific dimensions.
Showing first 48 of 660 sizes. Use our quote form to request any specific size.
JIS B 2401 FAQ
What is the difference between JIS B 2401 P and G series?
P series is designed for fixed (static) applications such as flanges and covers. G series is designed for motion (dynamic) applications such as hydraulic cylinders and pneumatic actuators. The O-ring dimensions are the same, but the recommended groove dimensions differ.
Are JIS B 2401 and ISO 3601 sizes interchangeable?
For many common sizes, JIS B 2401 and ISO 3601 are close enough to be interchangeable in general industrial use. However, the ID increments and some cross-sections differ slightly. In precision Japanese OEM equipment, always specify JIS B 2401 for guaranteed fit.
What is JIS B 2401 V series used for?
V series is specifically for vacuum flanges and semiconductor processing equipment. These sizes are standardized for vacuum chamber sealing where leak-tightness and dimensional consistency are critical.
How do JIS B 2401 tolerances compare to ISO 3601?
JIS B 2401 tolerances are broadly similar to ISO 3601 Class B for general industrial applications. For precision applications, tighter tolerances can be specified by agreement with the manufacturer.
Do you supply JIS B 2401 O-ring kits?
Yes. We supply JIS B 2401 metric assortment kits covering the most common P and G series sizes. Custom kits with specific sizes, materials, and quantities are available with no minimum order quantity.