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AS568-440 O-Ring Size
400 series · 1/4" cross section · Industrial flanges and piping
Inside diameter × cross section
170.81 × 6.99 mm
6.725″ × 0.275″ ·
outside diameter 184.78 mm (7.275″)
Dimensions
| Dimension | Inches | Millimetres |
|---|---|---|
| Inside diameter (ID) | 6.725″ | 170.81 mm |
| Cross section (CS) | 0.275″ | 6.99 mm |
| Outside diameter (OD) | 7.275″ | 184.78 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 170.81 mm, because compression set is permanent. If your measurement came in a little under this and the cross section roughly matches, -440 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) |
|---|---|---|---|
| -439 | 164.46 | 6.475″ | 178.43 |
| -441 | 177.16 | 6.975″ | 191.13 |
| -438 | 158.11 | 6.225″ | 172.08 |
| -442 | 183.51 | 7.225″ | 197.48 |