What Is the Standard O-Ring Size in mm?

Struggling to find the right O-ring size for your application? Choosing a non-standard size can cause leaks, misalignment, or premature failure.

Standard O-ring sizes in millimeters are defined by global sizing systems such as ISO 3601, with common inside diameters ranging from 1 mm to over 400 mm and cross-sections from 1 mm to 8.4 mm.

Let’s break down the global sizing standards and help you select the correct O-ring dimensions for your sealing needs.

What Are the Standard O-Ring Size Systems?

Confused by AS568 vs. ISO vs. BS sizes?

The most widely used O-ring size standards are ISO 3601 (metric), AS568 (inch-based, USA), and BS1806 (UK). ISO 3601 defines O-rings using inside diameter (ID) and cross-sectional diameter (CS) in millimeters.

🌍 O-Ring Standards Overview:

How Are O-Rings Measured in mm?

Not sure how to measure an O-ring?

O-rings are defined by two dimensions: the inner diameter (ID) and the cross-sectional thickness (CS), both measured in millimeters.

🛠️ Example:

• A metric O-ring labeled 20 × 2.5 means:
  • Inside Diameter = 20 mm
  • Cross Section = 2.5 mm

Use a digital caliper⁴ to measure accurately. If the O-ring is stretched or swollen, refer to part drawings or manufacturer datasheets⁵.

Common ISO 3601 O-Ring Sizes⁶ in mm

Looking for the most typical sizes?

Here’s a selection of common standard metric O-ring sizes under ISO 3601:

Why Standard O-Ring Sizes Matter?

Still thinking about customizing your size?

Using a standard O-ring size ensures compatibility with commercial groove designs, reduces lead time, and lowers production cost.

✅ Benefits of ISO Standard Sizes⁷:

• Immediate availability from stock
• No tooling costs for molds
• Predictable compression set behavior
• Easy to design groove dimensions
• Meets DIN, SAE, and JIS equipment specs

Julong Rubber O-Ring Size Chart & Materials

Looking for a reliable supplier of metric O-rings⁸ with stable material quality⁹ and custom options? At Julong Rubber, we offer a wide range of standard and non-standard O-rings in NBR, FKM, Silicone, and more.

Our O-rings are manufactured with precision to ensure consistent sealing performance in hydraulic, automotive, and HVAC systems.

🧰 Julong Rubber O-Ring Dimension & Material Overview

(This is a partial list for display. For a complete specification sheet, please contact us.)

Brief Analysis

• Material Distribution: FKM/VITON is the most common material, appearing in over 40% of entries, followed by Silicone, EPDM, HNBR, and NBR. Fluorosilicone and Perfluoro rubber are less common, likely due to their specialized, high-cost applications.
• Dimension Range: Most O-rings have dimensions between 0.381.4 mm and 51.8 mm, suitable for standard industrial sealing applications. The first dimension (likely inner diameter) typically ranges from 0.38 to 5 mm, with the second dimension (cross-section) between 0.3 and 3 mm.
• Applications: FKM/VITON’s prevalence suggests its use in high-performance environments (e.g., aerospace, automotive) due to its chemical and thermal resistance. Silicone and EPDM are likely used in less demanding, cost-sensitive applications.

✅ Available Materials:

Conclusion

Standard O-ring sizes in mm are defined by ISO 3601, which covers a wide range of inner diameters and cross-sections for global compatibility. Measuring O-rings correctly and choosing a standard size will help you ensure sealing performance, reduce cost, and simplify inventory management.

📏 Need metric O-rings for your project?
Contact Julong Rubber or Request a Quote for custom or ISO standard O-rings in NBR, EPDM, Viton, or silicone.

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