Dimensions
Outside diameter is not a published AS568 dimension. The standard fixes the inside diameter and the cross section, and the outside diameter follows from them: OD = ID + 2 x CS. Every outside diameter on this site is that sum, not a figure read from a table, and it inherits both tolerances rather than carrying one of its own.
What the 1xx series is for
Hydraulic, pump and valve
Every dash number from 102 to 178 in this series has the same 0.103 inch (2.62 mm) cross section. Choosing a size is choosing a bore, and the cross section follows from the series - which is why a seal that is the right diameter but the wrong series will sit in the groove and still leak.
Fitting an AS568-144
The dimensions above are the free-state size of the moulded ring. Whether it seals depends on the gland: the squeeze applied to the cross section, the stretch on the inside diameter when it is fitted, and the room left for the material to expand into. Those come from the equipment maker or the seal manufacturer's gland tables, not from the size chart.
Material matters as much as size. The same AS568-144 is made in nitrile, fluorocarbon, EPDM, silicone and more, and they behave differently with temperature, pressure and the fluid being sealed. The dash number specifies the shape; it says nothing about the compound.
Frequently asked questions
What size is an AS568-144 O-ring?
Inside diameter 2.487 inches (63.17 mm), cross section 0.103 inches (2.62 mm), so an outside diameter of 2.693 inches (68.41 mm).
What is the cross section of a 144 O-ring?
0.103 inches (2.62 mm), plus or minus 0.003 inches. Every dash number in the 1xx series shares that cross section: hydraulic, pump and valve.
What is the outside diameter of AS568-144?
2.693 inches (68.41 mm). The standard tabulates inside diameter and cross section rather than outside diameter, so OD is ID plus two cross sections: 2.487 + 2 x 0.103 = 2.693 inches.
What is the tolerance on an AS568-144 O-ring?
Inside diameter is 2.487 plus or minus 0.020 inches. Cross section is 0.103 plus or minus 0.003 inches. These are dimensional tolerances on the moulded part and are separate from squeeze, stretch and gland design, which decide whether the seal actually works.
What this chart covers
This chart carries the five cross-section series - 0xx, 1xx, 2xx, 3xx and 4xx. It does NOT carry the 900 series, the 20 straight-thread boss gaskets AS568 also lists: those are boss seals rather than O-rings in the usual sense and are sized to the fitting, so they are left out rather than mixed in. Dash numbers -400 to -424 are carried and flagged: two of the four catalogues list them under AS568, and the AS568B list of 369 standard sizes does not.
Where these figures come from
Dimensions are as defined by SAE AS568B (aerospace size standard for O-rings). This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.
Every value on this page was cross-checked against 5 independent published sources: