O-RING TABLES | DESIGN SIMPLY EXPLAINED

The most important O-ring tables at a glance

The use of O-ring tables brings standardization and therefore safety.

Whether you are designing a technical system or procuring replacements for maintenance and repairs, there are clear advantages to using standard-compliant O-rings.

Even retrofitting existing machines or systems with standardized O-rings can be worthwhile due to lower follow-up costs.

However, there is one thing to bear in mind: Depending on the region of the world, industry or application, different O-ring standards with their own size tables dominate. Here you will find an overview of the current standards and their special features.

O-ring table

Size example

Origin

View table

AS568

12.42 x 1.78 mm

America

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ISO 3601

12.42 x 1.78 mm

International

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BS 1806

12.42 x 1.78 mm

Great Britain

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BS 4518

29.6 x 2.4 mm

Great Britain

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SMS 1586

17.3 x 2.4 mm

Sweden

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JIS B2401

34.4 x 3.1 mm

Japan

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NFT 47-501

32.5 x 2.65 mm

France

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Generic / Metric

20 x 2 mm

International

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#1 AS568 | O-ring tables

Size example: 12.42 x 1.78 mm
Cord thickness examples: 
1,78 | 2,62 | 3,53 | 5,33 | 6,99

The Society of Automotive Engineers (SAE) has published the dimension table for O-rings for the first time in 1971. 

Since then, there have been several revisions, with revision F currently being the valid edition. In practice, however, this distinction is not particularly relevant, as the O-ring sizes have not changed according to the table.

The standard represents a standard for the aviation industry and refers to O-rings for sealing applications and tube fittings with straight threads. 

O-rings to AS568 are available with cord thicknesses of approx. 1.02 mm to 6.99 mm and inner diameters of up to approx. 660 mm. However, the definition in inches is leading. 

Even in regions with a predominantly metric system, it can make sense to design seals according to this standard due to the easy availability of O-rings. O-rings from the AS568 table are available in many different materials. 

With the latest version of ISO360the cross-sectional diameters according to AS568 are identical except for deviations in the range of hundredths of a millimeter.

#2 ISO 3601 | O-ring tables

Size example: 12.42 x 1.78 mm
Cord thickness examples: 
1,78 | 1,8 | 2,62 | 2,65 | 3,53| 3,55 | 5,3 | 5,33 | 6,99

The ISO 3601 in its latest version comprises far more than just a table of standardized O-ring sizes. 

While permissible surface deviations (Part 3) have been part of the standard for some time, Part 5 now regulates even more topics. 

With this addition, the O-ring standard also covers formulations and quality requirements for O-rings. To this end, the standard primarily refers to the degree of vulcanization, which can be determined by means of hardness and compression set. 

The standard thus represents a comprehensive set of rules for the use of O-rings:

  • Part 1: Dimensions
  • Part 2: Installation spaces
  • Part 3: Surface defects
  • Part 4: Support rings
  • Part 5: Materials

These control areas cover the main influencing factors for a functioning sealing system. In addition, ISO 3601 also contains Part 4, which deals with the use of back-up rings.

#3 BS 1806 | O-ring tables

Size example: 12.42 x 1.78 mm
Examples of cord thicknesses: 1.78 | 2.62 | 3.53 | 5.33 | 6.99

This British Standard contains a table with inch dimensions for the inside diameter and cross-sectional diameter of O-rings.

The standard comprises five groups of O-ring cross-sections that correspond to AS568.

However, the table in BS 1806 also defines other intermediate sizes.

#4 BS 4518 | O-ring tables

Size example: 29.6 x 2.4 mm
Examples of line weights: 1.6 | 2.4 | 3.0 | 5.7 | 8.4

This is also a British standard. In this case, however, the size table for O-rings refers to metric dimensions.

Each O-ring dimension is given an ID, which is made up of the respective inner diameter (given in four digits in tenths of a millimeter) and the cross-section (also in tenths of a millimeter).

The two dimensions are separated by a hyphen, so that reference 0031-16 refers to an O-ring with an inner diameter of 3.1 mm and a cord thickness of 1.6 mm.

The table contains a total of 203 different sizes. 1.6 mm is also the smallest line thickness in the table, which goes up to 8.4 mm.

#5 SMS 1586 | O-ring tables

Size example: 17.3 x 2.4 mm
Examples of line weights: 1.6 | 2.4 | 3.0 | 5.7 | 8.4

SMS 1586 is the Swedish mechanical standard (Sveriges Mekanstandardisering) for O-rings.

The sizes in the size table are marked in the format ID x C/S. ID stands for the inside diameter in millimeters, C/S for the cross-sectional diameter in millimeters. In this respect, the standard corresponds to DIN 3771.

In addition, SMS 1586 introduces two application-related markings for O-rings:

  • D: static and dynamic applications
  • S: only for static applications

#6 JIS B2401 | O-ring tables

Size example: 34.4 x 3.1 mm
Examples of cord thicknesses: 1.5 | 2 | 2.4 | 3.1 | 5.7 | 8.4 | 10.0

The JIS B2401 standard is the Japanese industry standard for O-rings.

The table contains a series of O-rings in both metric and imperial dimensions.

As far as the metric dimensions are concerned, the standard includes the O-ring sizes according to the ISO 3601 table.

#7 NFT 47-501 | O-ring tables

Size example: 32.5 x 2.65 mm
Examples of line weights: 1.8 | 2.65 | 3.55 | 5.3 | 7.0

The dimension table of the French standard is similar to ISO 3601.

It also includes parts of DIN 3771, which relates to O-rings for fluid technology with special dimensional accuracy.

In addition to these standards, NF T 47-501 contains some specific designations for classes of O-rings.

#8 Generic / Metric Dimensions | O-Ring Tables

Size example: 20 x 2 mm
Examples of cord thicknesses: 1.0 | 1.5 | 2.0 | 2.5 | 3.0 | 3.5

In addition to the size tables of specific standards, O-rings can also be obtained in generic metric sizes.

These can correspond to a standard size from one or more tables, but do not have to. Although these are not necessarily O-rings in standardized dimensions, availability is generally good.

This is due to the fact that O-ring manufacturers have the appropriate tools for production on a broad basis. The C/S x ID format is also commonly used here.

#9 Advantages of standardized O-ring tables

Standardized O-rings should be used wherever possible. Price, availability and reliably high quality speak for standardized sealing elements.

  • Price: O-rings from standard lists are produced in large quantities using economical manufacturing processes. Manufacturers have the necessary tools and are prepared to meet the demand. For example, O-rings made from particularly high-quality materials can also be offered at attractive conditions.

  • Availability: The worst-case scenario is when an O-ring suddenly fails and loses its sealing effect during operation of a technical system.However, the short-term availability of sealing elements also plays an important role for planned maintenance. Finally, new O-rings should be used wherever possible without any previous damage caused by storage or similar. Common O-rings from standard lists are available at short notice and are usually even available from stock.

  • Quality: The manufacture of O-rings in special sizes requires special tools or different processes. It is much more difficult to ensure production conditions are as stable as in the routine production of standardized O-rings. This is also noticeable in the quality and therefore the reliability of the O-rings. O-rings in standardized sizes therefore tend to have lower tolerances and better material properties.

“I am convinced that we should share our knowledge with the world. I hope I have been able to answer all your questions. If you have any further questions, please feel free to contact us at any time. We will be happy to help you.”

Picture of Luke Williams
Luke Williams

Lord of the O-rings
Author of the sealing academy

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