Master O-Ring Size Chart

AS568 is the primary inch-based O-Ring size standard used across North America. Published by SAE, it defines dash numbers (for example AS568-214) that encode both cross-section series and inside diameter. The five main series are 0xx (≈1/16″ CS), 1xx (≈3/32″), 2xx (≈1/8″), 3xx (≈3/16″), and 4xx (≈1/4″), with extended 400-series sizes and tube-fitting boss seals covered separately. If a US print, BOM, or repair manual lists a dash number without another standard name, it almost always means AS568.

When to use this chart filter: US / SAE dash numbers, “-214 style” sizes, and nominal inch fractions (e.g. 1/8″ × 1″). Select the AS568 chip above to list only those sizes.

X-Rings (also called Quad-Rings®) use a four-lobed cross-section instead of a round cord. They are sized on the same AS568 dash system as standard O-Rings: the same inside diameter (ID) and overall cross-section (CS) as the companion dash. The lobed profile adds more sealing surfaces, reduces spiral twist in reciprocating glands, and often needs less squeeze than a round O-Ring. Catalogs still sell them as AS568-214 X-Rings (or similar).

When to use this chart filter: prints that call out X-ring, quad-ring, or four-lobed seals by AS568 dash. Select X-Ring to view the AS568-compatible size list for that profile.

Square rings (square-cut or square-profile seals) are designed to fit AS568 glands but are not dimensionally identical to round O-Rings. They keep the same dash number and inside diameter, while the wall (CS) is slightly thinner than the matching AS568 round cord so the square section packs correctly in the groove. Use this filter when you measure a square cord or a drawing specifies square-cut washers / square rings by dash.

When to use this chart filter: square-profile seals sold under AS568 dash numbers. Select Square Ring — do not assume round O-Ring CS values for these parts.

AS568 Backup covers contoured back-up rings sized to the same dash numbers as AS568 O-Rings. These rings sit beside the O-Ring to block extrusion into the clearance gap under high pressure. Selecting this chip switches the chart headers from O-Ring CS/ID/OD columns to full back-up dimensions: ID, radial width (W), axial height (HT), contour radius, and contour height (inch and mm, with tolerances where published).

When to use this chart filter: high-pressure glands, “back-up ring” or anti-extrusion callouts, or matching a dash to PTFE / elastomer back-up stock. Select AS568 Backup only (exclusive) so the table shows back-up columns.

ORB Boss covers the AS568 900-series O-Rings used as straight-thread tube-fitting boss seals (SAE ORB / hydraulic fittings). These are not the same as the 0xx–4xx face or radial seal dashes: codes run roughly AS568-901 through AS568-932 with fitting-specific cross-sections and IDs. They seal the boss face under a fitting nut rather than a typical rectangular O-Ring groove.

When to use this chart filter: ORB / boss seal callouts, 9xx dash numbers, or hydraulic fitting kits. Select ORB Boss (not plain AS568) so 900-series sizes appear alone.

BS 1806 is the British Standards Institution chart of imperial O-Ring sizes. It is largely aligned with AS568 dash numbering for common sizes and has been superseded in many contexts by BS ISO 3601, but legacy UK drawings and spares still list BS 1806. This chart includes AS568-aligned dashes plus additional imperial sizes that appear on published BS 1806 lists.

When to use this chart filter: UK imperial prints, older British equipment manuals, or parts marked BS 1806. Cross-check AS568 if the dash looks familiar — many sizes match.

ISO 3601 is the international metric O-Ring size standard. It defines preferred metric inside diameters and cross-sections for global use. Class A sizes are intended to align with inch AS568 dimensions for interchangeability; other classes cover broader metric tooling. On this site, metric sizes are shown with The O-Ring Store code format CS × ID (for example 1.50X010 = 1.50 mm CS × 10 mm ID).

When to use this chart filter: metric drawings, ISO callouts, or when you measured CS and ID in millimeters. Select ISO 3601 and search by mm dimensions or CS×ID code.

JIS B 2401 is the Japanese Industrial Standard for O-Ring sizes, often called “Japanese metrics.” Sizes are grouped into series codes such as S (moving / packing), P (fixed / packing), G (static), and V (vacuum), with codes like P22 or G50. Dimensions are metric (ID × CS in mm). Japanese OEMs, hydraulics, and import equipment commonly use JIS series rather than AS568 dashes.

When to use this chart filter: Japanese equipment, JIS S/P/G/V codes on prints, or replacements ordered as “JIS P-…” Select JIS B 2401 and search the series code.

BS 4518 is the British Standards Institution standard for metric O-Ring sizes used in the UK and related markets. Unlike BS 1806 (imperial dashes), BS 4518 sizes are specified by metric ID and cross-section. On this chart they appear as store CS × ID codes for easy ordering and measurement matching.

When to use this chart filter: UK metric drawings, BS 4518 callouts, or metric spares for British equipment that is not ISO 3601 Class A / AS568-aligned.

DIN 3771 is the German Institute for Standardization (Deutsches Institut für Normung) size system for O-Rings, widely referenced in Germany and the EU. Sizes are given as ID × cross-section in millimeters. Many European machine tools, automotive, and industrial hydraulics list DIN dimensions even when the part is also available under ISO 3601.

When to use this chart filter: German or DIN-marked prints, European OEM spares, or metric CS×ID codes from DIN catalogs. Select DIN 3771.

SMS 1586 is the Swedish Mechanical Standard (Sveriges Mekanstandardisering) for O-Rings, used across Sweden and Nordic industry. Like other European metric systems, sizes are identified by inside diameter and cross-section in mm. Nordic equipment manuals and distributor catalogs often cite SMS even when dimensions overlap other metric standards.

When to use this chart filter: Swedish/Nordic equipment, SMS 1586 references, or metric CS×ID from Nordic catalogs. Select SMS 1586.

NF T 47-501 is the French Standards Institute (AFNOR) O-Ring size standard. It is closely related to ISO 3601-1 metric practice and is common on French industrial and automotive drawings. Sizes are metric ID × CS; this chart lists them in store CS × ID format for search and ordering.

When to use this chart filter: French prints, NF T 47-501 or AFNOR callouts, or metric replacements for French OEM equipment. Select NF T 47-501.

ISO 6149 specifies O-Rings for metric tube fittings and ports (metric parallel threads with elastomeric seals). Each size is tied to a port thread (for example M10×1, M18×1.5) as well as ID and CS. This is the metric counterpart to inch ORB boss seals: fitting geometry, not a general face-seal groove chart.

When to use this chart filter: metric port/fitting seals, ISO 6149 or “metric ORB-style” callouts. Select ISO 6149 — Series shows the port thread.

Generic metric sizes are widely tooled metric ID × CS combinations that may not map 1:1 to a single formal standard row, but appear constantly in catalogs and custom molds. Factories stock or tool these “common metrics” because OEMs specify rounded millimeter sizes that sit between formal ISO/DIN preferred lists. Codes use CS × ID (e.g. 2.00X025).

When to use this chart filter: you measured a metric ring that does not match AS568 or a named JIS/ISO dash, or a drawing only gives mm ID and CS. Select Generic Metric and search dimensions.

Parker 500 Series (codes like 5-002 through 5-1105) is Parker’s catalog of nonstandard O-Ring sizes that fall outside AS568 and are not pure “standard metric” either. Parker established tooling for these common specials so distributors can stock them by the 5-XXX number. Dimensions are listed in both inches and millimeters; they are not interchangeable with AS568 dashes of similar numbers.

When to use this chart filter: parts marked 5-xxx, Parker packing lists, or cross-references to Parker Series 5. Select Parker 500 and search the 5- number.