We are a leading manufacturer and distributor of custom and standard O-Rings. Shortly after o-rings first came into common use, it became obvious that standards for o-ring sizes, tolerances would be beneficial. Various government and engineering organizations have produced a multitude of o-ring standards. Here we present a brief overview of what we believe to be the most often used/referenced standards by our customers. You will also find a link to a size chart showing all known sizes for each standard.
International O-Ring Size Reference Table
Types of Standard O-Ring
The AS 568 o-ring size standard is published by the Society of
The BS 1806 o-ring size guide was issued by the British Standards Institution and lists all Imperial standard sizes. This standard includes all 5 of the main cross-section groups in AS568 plus several sizes that are “between” AS568 Sizes. BS 1806 has been superseded by BS ISO 3601, however, since BS 1806 is still widely referenced in certain industries/regions of the world, it is still relevant for cross-reference purposes.
Issued by the International Organization for Standardization, the ISO 3601 standard contains two groups of orings, Class A & Class B.
Class A corresponds to the American standard AS 568B in its current format (the 900 series tube fitting o-rings are not included). The ISO 3601-1 Size Code for these o-rings is the same as the AS 568 dash number.
Class B allows substitution of o-rings in technically acceptable and economical “metric” sizes, which can then fit into metric grooves. The first digit of the Size Code indicates the cross-section group (A-E), while the last four digits indicate the o-ring inside diameter rounded to the one-tenth millimeter.
Issued by the British Standards Institution, Standard BS 4518 identifies British Standard metric sizes. The size code for these o-rings is a four digit number indicating the o-ring I.D. in tenths of millimeters followed by a hyphen and two digits indicating the o-ring Cross Section, also in tenths of a millimeter
SMS 1586 refers to Swedish Mechanical Standard for o-rings (Sveriges Mekanstandardisering). In this standard, o-rings are simply identified by ID and C/S, similar to DIN 3771. Additionally, all SMS 1586 o-rings are classified into two groups. The first group, intended for dynamic and static installations is indicated in our table by the letter D. The second group, intended mainly for static applications, is indicated with an S.
The DIN 3771 o-ring standard is issued by The German Institute for Standards (Deutsches Institut für Normung). This standard identifies o-ring sizes by the ID x C/S and may be followed by a letter indicating the quality level (N – normal quality; S – special quality), and a code indicating the rubber polymer and IRHD hardness.
NF T 47-501
NFT 47-501 is issued by the Association Française de Normalisation (French Standards Institute). It is very similar to ISO 3601-1 in both the sizes included & the size reference. The size reference codes are designated with a letter corresponding to each of 5 cross-section groups (A-E), 4 digits indicating ID (rounded to 0.1 mm), a 2nd letter indicating Precision Class & a 3rd letter indicating Visual (inspection) Class. The Precision Class is indicated by the letter A (for Aerospace applications) or G (for General Purpose applications). The visual classes are N (1.0 AQL) and S (.65 AQL).
JIS B 2401
JIS B 2401 is a Japanese Industrial Standard for o-ring sizes. This standard, often referred to as “Japanese Metrics”, is organized into four series, based on their application. The o-rings in each section have ascending number codes to complete the size reference.
ISO 6149 specifies o-rings designed for use in Metric Tube Fittings. This standard includes 13 different sizes and calls out the metric thread size for each o-ring size.