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AS568-309 O-Ring Size
300 series · 3/16" cross section · Heavy hydraulics, higher pressure
Inside diameter × cross section
10.46 × 5.33 mm
0.412″ × 0.21″ ·
outside diameter 21.13 mm (0.832″)
Dimensions
| Dimension | Inches | Millimetres |
|---|---|---|
| Inside diameter (ID) | 0.412″ | 10.46 mm |
| Cross section (CS) | 0.21″ | 5.33 mm |
| Outside diameter (OD) | 0.832″ | 21.13 mm |
Outside diameter is not measured, it is derived: OD = ID + 2 × CS.
If your measured OD disagrees with this, trust the ID and cross section — measuring
across the outside of a flexible ring is the least reliable of the three.
If you measured a used one
A ring pulled out of service will measure smaller than 10.46 mm, because compression set is permanent. If your measurement came in a little under this and the cross section roughly matches, -309 is very likely still the correct part. Ordering the size your worn ring measures is how the same failure repeats. More on this →
Nearby sizes in the 300 series
These share the same 3/16" cross section, so if the thickness is right but the diameter is off, your ring is probably one of these.
| Dash | ID (mm) | ID (in) | OD (mm) |
|---|---|---|---|
| -310 | 12.06 | 0.475″ | 22.73 |
| -311 | 13.64 | 0.537″ | 24.31 |
| -312 | 15.24 | 0.6″ | 25.91 |
| -313 | 16.81 | 0.662″ | 27.48 |