AS568 O-ring sizes
AS568 is the standard list of inch O-ring sizes used across the United States. It is published by SAE International. Each size has a dash number, such as -214, that fixes the inside diameter, the cross-section and their tolerances.
AS568 does not set the material or the hardness. Name those separately.
Dash number series
The first digit of a three-digit dash number gives the cross-section. The smallest sizes, -001 to -003, have their own smaller cross-sections.
| Dash numbers | Nominal cross-section | Actual (in.) | Actual (mm) |
|---|---|---|---|
| -004 to -050 | 1/16 in. | 0.070 ± 0.003 | 1.78 ± 0.08 |
| -102 to -178 | 3/32 in. | 0.103 ± 0.003 | 2.62 ± 0.08 |
| -201 to -284 | 1/8 in. | 0.139 ± 0.004 | 3.53 ± 0.10 |
| -309 to -395 | 3/16 in. | 0.210 ± 0.005 | 5.33 ± 0.13 |
| -425 to -475 | 1/4 in. | 0.275 ± 0.006 | 6.99 ± 0.15 |
Sizes -901 to -932 are for straight-thread tube fitting bosses. They are listed by tube size rather than by a cross-section series.
How to specify an AS568 O-ring
Give the dash number, the material and the hardness, for example: AS568-214, Nitrile (NBR), 70 Shore A. A 70 durometer nitrile is a common general-purpose choice for oil and hydraulic service. For other fluids and temperatures, see the material pages.
AS568 sizes in our catalog
Our catalog lists every AS568 size with its inch and metric dimensions. Add the sizes you need to a quote request and name the material and durometer for each.
Questions we hear
- What does the first digit of an AS568 dash number mean?
- It gives the cross-section series: 0 for 1/16 in. (-004 to -050), 1 for 3/32 in., 2 for 1/8 in., 3 for 3/16 in. and 4 for 1/4 in. The -9xx sizes are for straight-thread tube fitting bosses.
- Does AS568 specify the O-ring material?
- No. AS568 covers sizes and tolerances only. Name the material and hardness separately, or send the full spec from your drawing.
- What if the size I need is not in AS568?
- Send the inside diameter and cross-section you need, or a drawing or sample. We make non-standard O-rings, including large spliced rings.
Request a quote
Send us a drawing, a sample part or a rough sketch. We will review it, recommend the right material and process, and give you a firm ship date with your quote.
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