AS568-909 O-Ring — 0.706 × 0.097 in
The -909 is a 900 series size: a 0.097 in cord on a 0.706 in inside diameter, which is 2.46 mm on 17.93 mm. Its outside diameter is 0.900 in (22.86 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) | 0.706 | 17.93 |
| Cross-section d₂ (cord) | 0.097 | 2.46 |
| Outside diameter (reference) | 0.900 | 22.86 |
| Inside diameter tolerance | ±0.009 | ±0.23 |
| Cross-section tolerance | ±0.003 | ±0.08 |
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 AS568-909 is a dimension
The -909 is a lookup key. Its first digit — 9 — puts it in the 900 Series family, and the remaining two digits are its position inside that family counted upwards by inside diameter, which makes it number 9 of the 20 sizes here. Neither digit group carries a size: the -909 is 0.706 in on a 0.097 in cord, and a dash number one away from it can differ by a hundredth of an inch or by a quarter of one.
This is a 900-series boss gasket, not an O-ring for a groove: it seals the joint between a straight-thread tube fitting and the boss it screws into, and its dash number follows the tube the port is cut for rather than the seal’s own geometry. Its cord is 0.097 in, which is one of 9 cord sizes used across this series — the 900 series is not a cord family.