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AS568-438 O-Ring Size
400 series · 1/4" cross section · Industrial flanges and piping
Inside diameter × cross section
158.11 × 6.99 mm
6.225″ × 0.275″ ·
outside diameter 172.08 mm (6.775″)
Dimensions
| Dimension | Inches | Millimetres |
|---|---|---|
| Inside diameter (ID) | 6.225″ | 158.11 mm |
| Cross section (CS) | 0.275″ | 6.99 mm |
| Outside diameter (OD) | 6.775″ | 172.08 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 158.11 mm, because compression set is permanent. If your measurement came in a little under this and the cross section roughly matches, -438 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 400 series
These share the same 1/4" 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) |
|---|---|---|---|
| -437 | 151.76 | 5.975″ | 165.73 |
| -439 | 164.46 | 6.475″ | 178.43 |
| -436 | 148.59 | 5.85″ | 162.56 |
| -435 | 145.41 | 5.725″ | 159.38 |