AS568 O-Ring Size Chart (Dash Numbers)

History of AS568 Master O-Ring Size Chart Shop AS568 O-Rings

AS568 is the North American inch size standard. If a US print lists a dash like -214 without naming another standard, it almost always means AS568. Tables below cover every standard dash in the five cross-section series.

Dimensions are actual AS568 sizes (not nominal fractions alone). OD = ID + 2×CS. Code links open a product search on theoringstore.com. For multi-standard search (ISO, JIS, BS, DIN, X-Ring, Square Ring, ORB Boss), use the Master O-Ring Size Chart.

0xx series — ~1/16″ (0.070″) cross-section

Dash range AS568-001 … 050 · Cross-section 0.040″–0.070″ (1.02–1.78 mm) · 50 sizes

1xx series — ~3/32″ (0.103″) cross-section

Dash range AS568-102 … 178 · Cross-section 0.103″ (2.62 mm) · 77 sizes

2xx series — ~1/8″ (0.139″) cross-section

Dash range AS568-201 … 284 · Cross-section 0.139″ (3.53 mm) · 84 sizes

3xx series — ~3/16″ (0.210″) cross-section

Dash range AS568-309 … 395 · Cross-section 0.210″ (5.33 mm) · 87 sizes

4xx series — ~1/4″ (0.275″) cross-section

Dash range AS568-425 … 475 · Cross-section 0.275″ (6.99 mm) · 76 sizes

Source: ANSI/SAE AS568 aerospace size standard for O-Rings. Boss / tube-fitting seals (AS568-901…932) are listed under ORB Boss on the Master O-Ring Size Chart and in SAE J1926 ORB Boss O-Rings.

How to read an AS568 dash number

OD = ID + 2 × CS. Tolerances are the AS568 published limits for standard (AN) shrinkage compounds. The 900-series boss seals for SAE ORB ports are listed separately on the ORB Boss Size Chart.

Other size charts

Related

• Sizing overview
• Master O-Ring Size Chart
• SAE J1926 ORB Boss O-Rings
• Shore A Hardness

History and explanation of the AS568 standard

What AS568 is

AS568 (Aerospace Size Standard for O-Rings) is an SAE International aerospace standard. It defines inside diameter (ID), cross-section (CS / width), tolerances, and the dash-number size codes used to order O-Rings. It also covers sizes used as straight-thread tube-fitting boss gaskets (the 900-series).

Important: AS568 is a size standard. It does not specify rubber compound, durometer, color, or military material callouts. Those come from a separate material spec (for example an AMS, MIL, NSF, or FDA compound) on the same purchase order.

Why it exists

Before a shared size system, US aerospace, military, and industrial OEMs often used proprietary O-Ring dimensions. Spares did not interchange, tooling multiplied, and field repair was harder than it needed to be.

AS568 gave the industry one common language: a dash number that means the same ID and CS whether you buy from a distributor, an OEM kit, or a military packing list. That is why a -214 on a hydraulic print, a pump rebuild kit, and a bag from The O-Ring Store all point at the same geometry.

Who publishes it

SAE’s A-6C2 Seals Committee issued the original standard. SAE still maintains the document. The Department of Defense later adopted SAE-AS568 for packing and gasket use, which helped lock the dash system into US military and industrial practice.

Timeline of the standard

In everyday buying and BOMs, people say AS568, AS568A, AS568B, and so on interchangeably when they mean the dash size. The letter is the document revision; the -214 geometry is what you put on the bag.

How the dash system is organized

AS568 groups sizes by cross-section:

• -001 … -0xx — thin cords (about 1/16″ / 0.070″ and smaller for the first few dashes)
• -1xx — about 3/32″ (0.103″)
• -2xx — about 1/8″ (0.139″)
• -3xx — about 3/16″ (0.210″)
• -4xx — about 1/4″ (0.275″)
• -9xx — boss seals for straight-thread tube fittings (ORB), with fitting-specific cords

Within a series, larger dash numbers mean larger inside diameters. That is why learning the five series is enough to “read” most North American O-Ring callouts at a glance.

AS568 and the rest of the world

AS568 became so common that metric international standards eventually made room for it. ISO 3601 Class A sizes align with AS568 dimensions and tolerances so the same geometry can be inspected in millimeters. Other national systems (JIS, DIN, BS, and so on) remain separate naming systems—even when a size is “close.”

Practical rule on the shop floor:

• Print says -214 → AS568 (this page)
• Print says 25 × 3.55 or a CS×ID store code → Metric / ISO chart
• Print says P22 / G50 → JIS B 2401 chart
• Print says ORB -8 / boss seal → ORB Boss chart

What AS568 does not tell you

AS568 will not pick the elastomer. For that you still need fluid, temperature, pressure, and approvals—see Materials, the Chemical Compatibility Chart, and Shore A Hardness.

It also will not design the groove. Squeeze, stretch, and gland depth live on the Groove Charts and in the controlling drawing.

Using this chart with the standard

1. Find the dash on the tables above (or measure ID and CS and match the nearest row).
2. Confirm tolerances if the print calls a specific AS568 revision or inspection method.
3. Add the compound and duro your application needs.
4. Order by dash + material—or open the Master O-Ring Size Chart when you need other standards in the same search.

Shop stocked AS568 sizes: AS568 O-Rings at The O-Ring Store.