O-Ring Size Chart — AS568 Dash Numbers, ID & Cross-Section
AS568 O-ring dash sizes: inside diameter, cross-section, tolerances, and computed OD for the five standard cross-section series.
Updated August 20, 2026
SAE AS568 is the U.S. standard dash-number system for O-rings: the first digit of the three-digit dash sets the cross-section (the −0xx series is 0.070″, −1xx is 0.103″, −2xx is 0.139″, −3xx is 0.210″, −4xx is 0.275″), and the remaining digits step through inside diameters, mostly in 1/16″ nominal increments. An O-ring is specified by ID and cross-section — never by OD, which is just ID + 2 × CS and is computed, not standardized. The actual ID always runs a few thousandths under the fractional nominal (a "1 inch" −214 measures 0.984″) so the ring stretches slightly onto its groove.
The tables below carry one continuous dash run per cross-section series, aimed at the sizes common in plumbing, hydraulic, and equipment repair work; each run stops where the digit-by-digit source verification stopped, and no row in between is skipped. ID tolerances grow with diameter (from ±0.005″ on small rings to ±0.040″ at 6-1/2″), while the cross-section tolerance is fixed per series. To identify an unknown ring, measure the cross-section first — it tells you the series — then measure the ID and find the nearest row; if the ring falls between rows, it is likely metric or a special.
0.070″ Cross-Section — Dashes −006 to −020
| Dash no. | ID (in) | ID tolerance | CS (in) | OD, computed (in) |
|---|---|---|---|---|
| -006 | 0.114 | ±0.005 | 0.070 ±0.003 | 0.254 |
| -007 | 0.145 | ±0.005 | 0.070 ±0.003 | 0.285 |
| -008 | 0.176 | ±0.005 | 0.070 ±0.003 | 0.316 |
| -009 | 0.208 | ±0.005 | 0.070 ±0.003 | 0.348 |
| -010 | 0.239 | ±0.005 | 0.070 ±0.003 | 0.379 |
| -011 | 0.301 | ±0.005 | 0.070 ±0.003 | 0.441 |
| -012 | 0.364 | ±0.005 | 0.070 ±0.003 | 0.504 |
| -013 | 0.426 | ±0.005 | 0.070 ±0.003 | 0.566 |
| -014 | 0.489 | ±0.005 | 0.070 ±0.003 | 0.629 |
| -015 | 0.551 | ±0.007 | 0.070 ±0.003 | 0.691 |
| -016 | 0.614 | ±0.009 | 0.070 ±0.003 | 0.754 |
| -017 | 0.676 | ±0.009 | 0.070 ±0.003 | 0.816 |
| -018 | 0.739 | ±0.009 | 0.070 ±0.003 | 0.879 |
| -019 | 0.801 | ±0.009 | 0.070 ±0.003 | 0.941 |
| -020 | 0.864 | ±0.009 | 0.070 ±0.003 | 1.004 |
OD computed as ID + 2 × CS. Tolerances per the AS568 tables as republished by MFP and Freudenberg (FST); dimensions are for the ring itself, not the groove.
0.103″ Cross-Section — Dashes −110 to −124
| Dash no. | ID (in) | ID tolerance | CS (in) | OD, computed (in) |
|---|---|---|---|---|
| -110 | 0.362 | ±0.005 | 0.103 ±0.003 | 0.568 |
| -111 | 0.424 | ±0.005 | 0.103 ±0.003 | 0.630 |
| -112 | 0.487 | ±0.005 | 0.103 ±0.003 | 0.693 |
| -113 | 0.549 | ±0.007 | 0.103 ±0.003 | 0.755 |
| -114 | 0.612 | ±0.009 | 0.103 ±0.003 | 0.818 |
| -115 | 0.674 | ±0.009 | 0.103 ±0.003 | 0.880 |
| -116 | 0.737 | ±0.009 | 0.103 ±0.003 | 0.943 |
| -117 | 0.799 | ±0.010 | 0.103 ±0.003 | 1.005 |
| -118 | 0.862 | ±0.010 | 0.103 ±0.003 | 1.068 |
| -119 | 0.924 | ±0.010 | 0.103 ±0.003 | 1.130 |
| -120 | 0.987 | ±0.010 | 0.103 ±0.003 | 1.193 |
| -121 | 1.049 | ±0.010 | 0.103 ±0.003 | 1.255 |
| -122 | 1.112 | ±0.010 | 0.103 ±0.003 | 1.318 |
| -123 | 1.174 | ±0.012 | 0.103 ±0.003 | 1.380 |
| -124 | 1.237 | ±0.012 | 0.103 ±0.003 | 1.443 |
OD computed as ID + 2 × CS. Tolerances per the AS568 tables as republished by MFP and Freudenberg (FST); dimensions are for the ring itself, not the groove.
0.139″ Cross-Section — Dashes −210 to −224
| Dash no. | ID (in) | ID tolerance | CS (in) | OD, computed (in) |
|---|---|---|---|---|
| -210 | 0.734 | ±0.010 | 0.139 ±0.004 | 1.012 |
| -211 | 0.796 | ±0.010 | 0.139 ±0.004 | 1.074 |
| -212 | 0.859 | ±0.010 | 0.139 ±0.004 | 1.137 |
| -213 | 0.921 | ±0.010 | 0.139 ±0.004 | 1.199 |
| -214 | 0.984 | ±0.010 | 0.139 ±0.004 | 1.262 |
| -215 | 1.046 | ±0.010 | 0.139 ±0.004 | 1.324 |
| -216 | 1.109 | ±0.012 | 0.139 ±0.004 | 1.387 |
| -217 | 1.171 | ±0.012 | 0.139 ±0.004 | 1.449 |
| -218 | 1.234 | ±0.012 | 0.139 ±0.004 | 1.512 |
| -219 | 1.296 | ±0.012 | 0.139 ±0.004 | 1.574 |
| -220 | 1.359 | ±0.012 | 0.139 ±0.004 | 1.637 |
| -221 | 1.421 | ±0.012 | 0.139 ±0.004 | 1.699 |
| -222 | 1.484 | ±0.015 | 0.139 ±0.004 | 1.762 |
| -223 | 1.609 | ±0.015 | 0.139 ±0.004 | 1.887 |
| -224 | 1.734 | ±0.015 | 0.139 ±0.004 | 2.012 |
OD computed as ID + 2 × CS. Tolerances per the AS568 tables as republished by MFP and Freudenberg (FST); dimensions are for the ring itself, not the groove.
0.210″ Cross-Section — Dashes −310 to −324
| Dash no. | ID (in) | ID tolerance | CS (in) | OD, computed (in) |
|---|---|---|---|---|
| -310 | 0.475 | ±0.005 | 0.210 ±0.005 | 0.895 |
| -311 | 0.537 | ±0.007 | 0.210 ±0.005 | 0.957 |
| -312 | 0.600 | ±0.009 | 0.210 ±0.005 | 1.020 |
| -313 | 0.662 | ±0.009 | 0.210 ±0.005 | 1.082 |
| -314 | 0.725 | ±0.010 | 0.210 ±0.005 | 1.145 |
| -315 | 0.787 | ±0.010 | 0.210 ±0.005 | 1.207 |
| -316 | 0.850 | ±0.010 | 0.210 ±0.005 | 1.270 |
| -317 | 0.912 | ±0.010 | 0.210 ±0.005 | 1.332 |
| -318 | 0.975 | ±0.010 | 0.210 ±0.005 | 1.395 |
| -319 | 1.037 | ±0.010 | 0.210 ±0.005 | 1.457 |
| -320 | 1.100 | ±0.012 | 0.210 ±0.005 | 1.520 |
| -321 | 1.162 | ±0.012 | 0.210 ±0.005 | 1.582 |
| -322 | 1.225 | ±0.012 | 0.210 ±0.005 | 1.645 |
| -323 | 1.287 | ±0.012 | 0.210 ±0.005 | 1.707 |
| -324 | 1.350 | ±0.012 | 0.210 ±0.005 | 1.770 |
OD computed as ID + 2 × CS. Tolerances per the AS568 tables as republished by MFP and Freudenberg (FST); dimensions are for the ring itself, not the groove.
0.275″ Cross-Section — Dashes −425 to −439
| Dash no. | ID (in) | ID tolerance | CS (in) | OD, computed (in) |
|---|---|---|---|---|
| -425 | 4.475 | ±0.033 | 0.275 ±0.006 | 5.025 |
| -426 | 4.600 | ±0.033 | 0.275 ±0.006 | 5.150 |
| -427 | 4.725 | ±0.033 | 0.275 ±0.006 | 5.275 |
| -428 | 4.850 | ±0.033 | 0.275 ±0.006 | 5.400 |
| -429 | 4.975 | ±0.037 | 0.275 ±0.006 | 5.525 |
| -430 | 5.100 | ±0.037 | 0.275 ±0.006 | 5.650 |
| -431 | 5.225 | ±0.037 | 0.275 ±0.006 | 5.775 |
| -432 | 5.350 | ±0.037 | 0.275 ±0.006 | 5.900 |
| -433 | 5.475 | ±0.037 | 0.275 ±0.006 | 6.025 |
| -434 | 5.600 | ±0.037 | 0.275 ±0.006 | 6.150 |
| -435 | 5.725 | ±0.037 | 0.275 ±0.006 | 6.275 |
| -436 | 5.850 | ±0.037 | 0.275 ±0.006 | 6.400 |
| -437 | 5.975 | ±0.037 | 0.275 ±0.006 | 6.525 |
| -438 | 6.225 | ±0.040 | 0.275 ±0.006 | 6.775 |
| -439 | 6.475 | ±0.040 | 0.275 ±0.006 | 7.025 |
OD computed as ID + 2 × CS. The 0.275″ series run starts at −425; the −4xx dashes below 4-1/2″ ID could not be verified across both reproductions and are omitted rather than transcribed from a single source.
Sources & Further Reading
- SAE AS568 (Aerospace Size Standard for O-Rings) — the dash-number system; dimensions transcribed from published reproductions, not the SAE original
- MFP Sealing Technologies, "O-Ring Standard Sizes — AS 568D" chart — first reproduction, all shipped cells
- Freudenberg Sealing Technologies, "O-Ring Reference AS568 Sizes" guide — second independent reproduction; every shipped cell digit-identical to the MFP chart (compared programmatically)
Frequently Asked Questions
How do I measure an O-ring to find its dash number?
Measure the cross-section (thickness) first with calipers — it lands on one of five values: 0.070, 0.103, 0.139, 0.210, or 0.275 in, which picks the series. Then measure the ID and match it to the nearest table row. Measure a used ring loosely: rubber swells in service, so the CS reads high and the ID low. A ring that falls between rows is probably metric (ISO 3601) or a manufacturer special.
Why is the OD column marked "computed"?
AS568 standardizes only ID and cross-section; the OD is their arithmetic consequence (OD = ID + 2 × CS) and is listed purely for convenience — a −214 is 0.984 + 2 × 0.139 = 1.262 in across. Suppliers print the same computed value. Groove design also works from ID and CS: the ID sets the stretch on the gland, the CS sets the squeeze.
What does a dash number like -112 actually encode?
The leading digit is the cross-section family (1 = 0.103 in) and the rest is a sequence position along the ID ladder — it is a catalog index, not a dimension. Within a series the IDs mostly climb in 1/16 in nominal steps. The −9xx series (not tabulated here) is the exception: those are straight-thread tube boss gaskets with their own non-uniform cross-sections.
Are AS568 and metric O-rings interchangeable?
Generally no. Metric rings follow ISO 3601 with cross-sections of 1.78, 2.62, 3.53, 5.33, and 6.99 mm — the first four are near-exact twins of the 0.070/0.103/0.139/0.210 in series, so those often do interchange — but metric ID steps land between the AS568 rows. Forcing a near-miss ring changes stretch and squeeze, the two numbers a groove is designed around, and marginal seals fail hot.
Try the Calculators
O-Ring Size Chart — AS568 Dash Numbers, ID & Cross-Section — reuven.tools/reference/o-ring-sizes — verified against: SAE AS568 (Aerospace Size Standard for O-Rings) — the dash-number system; dimensions transcribed from published reproductions, not the SAE original; MFP Sealing Technologies, "O-Ring Standard Sizes — AS 568D" chart — first reproduction, all shipped cells; Freudenberg Sealing Technologies, "O-Ring Reference AS568 Sizes" guide — second independent reproduction; every shipped cell digit-identical to the MFP chart (compared programmatically)