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O-Ring Size Chart (SAE AS568 Series)

The SAE AS568 o-ring series — nominal cross-section, tolerance and inside-diameter range for each series, plus how the dash number is read.

AS568 seriesDash rangeCS (in)CS (frac.)CS (mm)Tol. (in)Inside dia. range (in)
How to read a dash number: the series is the leading digit and the rest of the number identifies the individual inside diameter within that series — so -110 is the 100 series (0.103 in cross-section), and -210 is the 200 series. The last digit of a dash number gives a rough sense of size within the series, but it is not a formula: always look up the actual inside diameter rather than extrapolating. O-rings are specified by inside diameter and cross-section (not outside diameter), plus hardness in Shore A durometer — 70 is the common default, 75 for Viton. The standard was first published by SAE in 1971 and most recently revised as AS568D in 2014; AS568, AS568A through D all refer to the same dash sizes. Source: SAE AS568 (dash sizes), tolerances per ISO 3601-1A.

Standard: SAE AS568 / ISO 3601-1A  ·  Data checked: 2026-10-14

Frequently asked questions

How do I read a dash number like -110?

The leading digit is the series, which fixes the cross-section, and the rest identifies the inside diameter within it. So -110 is in the 100 series, cross-section 0.103 in. The number is an identifier, not a formula — always look up the actual inside diameter rather than extrapolating from the digits.

Do I measure the inside or outside diameter?

Inside diameter and cross-section, always. O-rings are specified that way because the inside diameter is what fits the groove and the cross-section sets the squeeze. Outside diameter is a derived figure and is only listed for reference.

What durometer should I use?

70 Shore A is the usual default and covers most static sealing. Go harder (90) for high pressure or where extrusion is a risk, softer (50) for very low pressure or delicate surfaces. Viton is commonly supplied at 75.

What is the difference between AS568, AS568A and AS568D?

' Nothing that changes the sizes — they are revisions of the same SAE document, published in 1971, 1974, 2001, 2008 and 2014. A -110 is a -110 in any of them. The later revisions added series and tolerance detail.

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