O-Ring Size Standards
An O-Ring is one of the most common types of seals in the world. O-Rings are used in a variety of applications in different industries around the world. Because of its popularity, there is virtually an unlimited number of possible sizes of an O-Ring. Thus, the need for size standards which cover the most common sizes used.
Over the years, many size standards have been developed for O-Rings. The table below shows what we believe to be the most often used/referenced standards by our customers in the United States and other countries.
**This information is only intended as a guide to identify O-Ring sizes from the various international standards. Although we believe this information to be correct, we cannot guarantee 100% accuracy with each and every standard. Therefore, we recommend referral to the actual specifications before proceeding with design work, etc. **
AS568 is the most commonly used standard in the United States for defining “inch sizes” of o-rings.
British Standards Institution and lists all Imperial standard sizes. It has been superseded by BS ISO 3601.
International Organization for Standardization and contains both Class A and Class B O-Rings.
Issued by the British Standards Institution, Standard BS 4518 identifies British Standard metric sizes.
Swedish Mechanical Standard (Sveriges Mekanstandardisering). O-Rings are identified by ID and C/S.
The German Institute for Standards (Duetsches Institut für Normung). O-Ring sizes shown as ID x C/S.
NF T 47-501
Association Française de Normalisation (French Standards Institute). Similar to ISO 3601-1.
JIS B 2401
Japanese Industrial Standard for O-Ring sizes. This standard, often referred to as “Japanese Metrics.”
ISO 6149 specifies O-Rings designed for use in Metric Tube Fittings. Includes 13 different sizes and calls out the metric thread size for each o-ring size.
Generic Metric O-Ring Sizes
Included are the most common metric sizes matching up with any corresponding international standard sizes.
Metric O-Ring Size Cross Reference Table
Common international size standards and allows cross-referencing to other standards.
Parker 500 Series O-Ring Sizes
5-XXX sizes are O-rings of nonstandard dimensions for which Parker has tooling
Some of the standards referenced here specify the acceptable tolerance ranges for the o-rings within that standard. However, With the exception of our AS568 size chart, our other size reference charts do not list tolerances, as these tend to vary between the standards issuing organizations. To view the size tolerances for the o-rings we sell, please refer to either the AS568 size chart for American Standard Sizes, or our Metric O-Ring Tolerances page for all other “metric” O-Rings.