AS568-439 O-Ring — 6.475 × 0.275 in
The -439 is a 400 series size: a 0.275 in cord on a 6.475 in inside diameter, which is 6.99 mm on 164.47 mm. Its outside diameter is 7.025 in (178.44 mm), derived as ID + 2 × cord.
Dimensionsthe two cells the standard fixes, and one derived value
| Dimension | Inches (AS568) | Millimetres (converted) |
|---|---|---|
| Inside diameter d₁ (ID) | 6.475 | 164.47 |
| Cross-section d₂ (cord) | 0.275 | 6.99 |
| Outside diameter (reference) | 7.025 | 178.44 |
| Inside diameter tolerance | ±0.040 | ±1.02 |
| Cross-section tolerance | ±0.006 | ±0.15 |
Inches are the standard’s own units; millimetre values are conversions — inch × 25.4, rounded to two decimals — and not the ISO 3601-1 metric sizes. Outside diameter is a reference value derived as ID + 2 × cross-section; the two diameters the standard fixes are the inside diameter and the cord.
Reading the designationnothing in AS568-439 is a dimension
The -439 is a lookup key. Its first digit — 4 — puts it in the 400 Series family, and the remaining two digits are its position inside that family counted upwards by inside diameter, which makes it number 15 of the 51 sizes here. Neither digit group carries a size: the -439 is 6.475 in on a 0.275 in cord, and a dash number one away from it can differ by a hundredth of an inch or by a quarter of one.
The same inside diameter, in another seriesa matching bore does not make two rings interchangeable
| Series | Dash | Cord (in) | Cord (mm) | ID tol. |
|---|---|---|---|---|
| 400 Series | -439 | 0.275 | 6.99 | ±0.040 |
| 300 Series | -363 | 0.210 | 5.33 | ±0.040 |
These rings share an inside diameter and nothing else. The cords differ, and so do the inside diameter tolerances on some of them — the tolerance is a per-size figure in the standard, not a function of the diameter, so it is printed rather than derived.