The AS568-901 through -932 O-ring sizes (Parker’s 3- series) are intended to be used for sealing straight thread tube fittings in a boss. The design charts below show the standard boss designs that are used for this purpose. These charts list port dimensions per AS5202 and J1926 and fitting ends per AS4395.
Both of these bosses use the same O-ring, but Parker Engineered Materials Group recommends using the port dimensions per J1926 when there is a choice. It is the newer design, and it has not been fully accepted yet by industry or by the military though there is a military standard for it. The J1926 dimensions provide for closer tolerance control of the O-ring cavity and distort the O-ring less when assembled. The improved tolerance condition assures much less trouble due to leakage resulting from insufficient squeeze or extrusion when the older cavity is too small. The reduced distortion gives a longer life.