AS568 O-Ring Dash Number Chart

What it is

SAE AS568 is the standard list of inch-size O-rings used across North American hydraulics. Each size has a dash number, such as -214. The dash number sets the inside diameter (ID) and cross section (CS). It does not set the material or hardness. Those are ordered separately (for example nitrile 70 durometer or FKM 90).

How to read it

• The first digit of a three-digit dash number tells you the cross-section series (see chart).
• The remaining digits step up the ID within that series. A higher number in the same series means a larger ID.
• 900 series O-rings are for SAE straight thread (ORB) ports. The last two digits are the tube OD in sixteenths of an inch, so -906 fits a -6 port.
• Look up the exact ID and tolerance in the AS568 table or the O-ring maker's catalog.

Series chart

Key points

• Nominal and actual sizes differ. Always use the actual ID and CS to check fit.
• Match the material to the fluid and temperature, and the durometer to the pressure and gap. The dash number does not do this.
• Metric O-rings (ISO 3601) are a separate system. Some sizes are close to AS568 sizes but are not the same.
• Measure a used O-ring with care. It may have swelled, shrunk or taken a set.

Common mistakes

• Ordering by dash number without specifying material and durometer.
• Measuring a stretched or flattened O-ring and picking the next size.
• Using a standard -0xx O-ring in an ORB port instead of the 900 series ring.

Governing standards: SAE AS568 (aerospace size standard for O-rings, used throughout industry); SAE J1926 (straight thread ports); ISO 3601 (metric O-rings); O-ring maker gland design data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.