O-Rings
An AS568 O-ring is bought by its dash number — call for a -214 and you get a ring with a 0.984 in inside diameter and a 0.139 in cord. The dash number is the whole specification, and it is a lookup rather than a formula: nothing in the digits can be multiplied, added or read off to get a dimension. This sub-library tabulates that lookup.
How to read a dash numberthe one designation in this library that carries no dimension at all
Everywhere else in this database a designation encodes a size. An M6 screw is 6 mm across the thread; a 6205 bearing has a 25 mm bore; HK1210 is 12 mm on a 10 mm wide cup. An AS568 dash number encodes nothing of the sort. It is an index into a table, and the table is the only place the dimensions exist.
What the digits do tell you is which cross-section family the ring belongs to, and that is worth knowing before you look anything up. The first digit gives the family: 0 is a 0.070 in cord, 1 is 0.103, 2 is 0.139, 3 is 0.210 and 4 is 0.275. The remaining two digits are the ring's position in that family, numbered upwards by inside diameter. So a -214 and a -114 are a hundred apart in the numbering and share nothing else: different cord families, and inside diameters with no arithmetic between them.
Three sizes break even that rule. The -001, -002 and -003 are smaller than the family they sit in — 0.040, 0.050 and 0.060 in cords against the 0.070 in of the rest of the 000 series, which is the thinnest cord this standard defines. They are the first three dash numbers ever assigned and they were never moved into a family of their own.
The 900 series is a different thing wearing the same numbering. Those are boss gaskets — the seals that go under a straight-thread tube fitting to seal it against a port face — and their cords range from 0.056 to 0.118 in with no consistent step. They belong to AS568 because the same standard that fixes the O-ring sizes fixes the port sizes they sit on, not because they share a cord.
The 6 seriesfive cord families, and one family that is not one
| Series | Code | Dash numbers | Cord | Sizes | Inside diameter |
|---|---|---|---|---|---|
| 000 Series | 0xx | -001 to -050 | 0.070 in (1.78 mm) + 3 thinner | 50 | 0.029–5.239 in (0.74–133.07 mm) |
| 100 Series | 1xx | -102 to -178 | 0.103 in (2.62 mm) | 77 | 0.049–9.737 in (1.24–247.32 mm) |
| 200 Series | 2xx | -201 to -284 | 0.139 in (3.53 mm) | 84 | 0.171–17.955 in (4.34–456.06 mm) |
| 300 Series | 3xx | -309 to -395 | 0.210 in (5.33 mm) | 87 | 0.412–25.940 in (10.46–658.88 mm) |
| 400 Series | 4xx | -425 to -475 | 0.275 in (6.99 mm) | 51 | 4.475–25.940 in (113.67–658.88 mm) |
| 900 Series | 9xx | -901 to -932 | Mixed — 9 different cords | 20 | 0.185–2.337 in (4.7–59.36 mm) |
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.
The 6 series do not tile the numbering between them: each starts and stops where the standard puts it, so a dash number missing from one table is not a size this library is holding back. The 369 sizes above are every size both source tables carry.
What this sub-library does not publishand the reason for each omission, because a missing number and a number that does not exist are different things
Material, hardness and temperature ratings
An O-ring's Shore A hardness and its service temperature range are set by the compound it is moulded from, not by the size, and every compound supplier prints its own figures for the same generic elastomer. The size table and the compound sheet are two documents. This library holds the first one.
Gland and groove dimensions
How deep and how wide to machine the groove is a separate standard — SAE AS4716 and AS4716A for the inch sizes, ISO 3601-2 for the metric ones — and it varies with whether the seal is static or dynamic and how much pressure it holds. A groove depth printed per dash number would look authoritative and be wrong for most uses.
Nominal fractional callouts
The tables consulted give the dimensions as decimals. One of them also prints a nominal fractional reading beside each size — 5/64 in for the -004, whose actual inside diameter is 0.070 in — and that reading appears in one table only, so no second source exists for the cell and it is not printed here. The same rule is why the families below are named by their cord rather than by the trade nickname for that cord: the nicknames are nominal fractions too, and they do not match the cord they name.
The inside diameter tolerance of -469 and -470
The two source tables agree on every cell of every other size. On these two they do not: one gives ±0.090 in, the other ±0.095 in, and the disagreement is real rather than a rounding difference. The dimension and the cross-section tolerance are printed; the inside diameter tolerance is left blank and marked, because choosing one of two conflicting values would hide the conflict.
What is not here yetplanned batches, and one standard this library cannot do honestly
Frequently asked questionsreading an AS568 dash number
Is an AS568 O-ring the same as an ISO 3601-1 one?
The cords are the same physical sizes: convert an AS568 cord to millimetres and you land within a few hundredths of a millimetre of the ISO cord for that size class. The inside diameters are a different matter. Each standard lists its own sequence of inside diameters within those cords, and the two sequences are not translations of one another — a metric size can sit a fraction of a millimetre from the nearest inch size, or a tenth of one. Convert the callout and check the gland; do not assume the sizes interchange because the cord lines up. The ISO 3601-1 table itself is not published here, and the roadmap below says why.
Where do these dimensions come from?
Two independent manufacturer tables, compared cell by cell: the Apple Rubber AS568 quick-reference chart (2022) and the Trelleborg Sealing Solutions AS568 catalogue (July 2022 edition). They agree on the inside diameter and the cross-section of every size listed here, and on all but two tolerance cells — those two are left blank and marked. Nothing on these pages is transcribed from a single table.
Why are the dimensions given in inches when the rest of this site is metric?
Because AS568 is an inch standard and the dash number has no meaning outside it. Millimetre values are printed beside every inch value, and they are conversions — inch multiplied by 25.4, rounded to two decimals — not an independent metric dimensioning. The conversion is an arithmetic step, and it is shown so it can be checked rather than trusted.