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AS568 O-Ring Dash Size Chart and Reference

AS568 assigns each standard inch-series O-ring a dash number that fixes its inside diameter and cross-section. This searchable chart lists nominal ID, cross-section, calculated OD and millimetre equivalents so estimators and buyers can confirm a size in seconds.

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Dash no.CS seriesNominal ID (in)Nominal CS (in)Nominal OD (in)ID (mm)CS (mm)
-004
0xx
0.07
0.07
0.21
1.778
1.778
-005
0xx
0.101
0.07
0.241
2.5654
1.778
-006
0xx
0.114
0.07
0.254
2.8956
1.778
-007
0xx
0.145
0.07
0.285
3.683
1.778
-008
0xx
0.176
0.07
0.316
4.4704
1.778
-009
0xx
0.208
0.07
0.348
5.2832
1.778
-010
0xx
0.239
0.07
0.379
6.0706
1.778
-011
0xx
0.301
0.07
0.441
7.6454
1.778
-012
0xx
0.364
0.07
0.504
9.2456
1.778
-013
0xx
0.426
0.07
0.566
10.8204
1.778
-014
0xx
0.489
0.07
0.629
12.4206
1.778
-015
0xx
0.551
0.07
0.691
13.9954
1.778
-016
0xx
0.614
0.07
0.754
15.5956
1.778
-017
0xx
0.676
0.07
0.816
17.1704
1.778
-018
0xx
0.739
0.07
0.879
18.7706
1.778
-019
0xx
0.801
0.07
0.941
20.3454
1.778
-020
0xx
0.864
0.07
1.004
21.9456
1.778
-102
1xx
0.049
0.103
0.255
1.2446
2.6162
-103
1xx
0.081
0.103
0.287
2.0574
2.6162
-104
1xx
0.112
0.103
0.318
2.8448
2.6162
-105
1xx
0.143
0.103
0.349
3.6322
2.6162
-106
1xx
0.174
0.103
0.38
4.4196
2.6162
-107
1xx
0.206
0.103
0.412
5.2324
2.6162
-108
1xx
0.237
0.103
0.443
6.0198
2.6162
-109
1xx
0.299
0.103
0.505
7.5946
2.6162
-110
1xx
0.362
0.103
0.568
9.1948
2.6162
-111
1xx
0.424
0.103
0.63
10.7696
2.6162
-112
1xx
0.487
0.103
0.693
12.3698
2.6162
-113
1xx
0.549
0.103
0.755
13.9446
2.6162
-114
1xx
0.612
0.103
0.818
15.5448
2.6162
-115
1xx
0.674
0.103
0.88
17.1196
2.6162
-116
1xx
0.737
0.103
0.943
18.7198
2.6162
-201
2xx
0.171
0.139
0.449
4.3434
3.5306
-202
2xx
0.234
0.139
0.512
5.9436
3.5306
-203
2xx
0.296
0.139
0.574
7.5184
3.5306
-204
2xx
0.359
0.139
0.637
9.1186
3.5306
-205
2xx
0.421
0.139
0.699
10.6934
3.5306
-206
2xx
0.484
0.139
0.762
12.2936
3.5306
-207
2xx
0.546
0.139
0.824
13.8684
3.5306
-208
2xx
0.609
0.139
0.887
15.4686
3.5306
-209
2xx
0.671
0.139
0.949
17.0434
3.5306
-210
2xx
0.734
0.139
1.012
18.6436
3.5306
-211
2xx
0.796
0.139
1.074
20.2184
3.5306
-212
2xx
0.859
0.139
1.137
21.8186
3.5306
-213
2xx
0.921
0.139
1.199
23.3934
3.5306
-214
2xx
0.984
0.139
1.262
24.9936
3.5306
-215
2xx
1.046
0.139
1.324
26.5684
3.5306
-216
2xx
1.109
0.139
1.387
28.1686
3.5306
-309
3xx
0.412
0.21
0.832
10.4648
5.334
-310
3xx
0.475
0.21
0.895
12.065
5.334
-311
3xx
0.537
0.21
0.957
13.6398
5.334
-312
3xx
0.6
0.21
1.02
15.24
5.334
-313
3xx
0.662
0.21
1.082
16.8148
5.334
-314
3xx
0.725
0.21
1.145
18.415
5.334
-315
3xx
0.787
0.21
1.207
19.9898
5.334
-316
3xx
0.85
0.21
1.27
21.59
5.334

Nominal values for the standard AS568 series, listed as a quick lookup. The 0xx series is 0.070 in, 1xx is 0.103 in, 2xx is 0.139 in, 3xx is 0.210 in and 4xx is 0.275 in nominal cross-section. Outside diameter is calculated as ID plus two cross-sections. Always confirm size and tolerances against the current AS568 standard and your supplier drawing; metric O-rings are not the same as AS568 inch sizes, even when close.

Clean up seal item descriptions

An optional review of how to normalise O-ring and seal item masters in your ERP.

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How to use the chart

Type a dash number such as 210, or an ID or series, into the search box to filter the table. Each row shows the nominal inside diameter and cross-section in inches, the calculated outside diameter and the metric conversions. Use it to confirm a customer's callout, cross-check a supplier quote line, or find the nearest standard size before you ask for a custom mould.

  • Dash numbers beginning 0 or 1 are the smaller 0.070 in and 0.103 in sections.
  • A 2xx dash is a 0.139 in section; 3xx is 0.210 in; 4xx is 0.275 in.
  • Drawings often write the size as 2-210 or AS568-210; both refer to the same dash 210 ring.

How the numbering works

AS568 dash numbers encode the cross-section series in the leading digit or digits and the ID size sequence in the last two. Within a series, nominal IDs step upward in fixed increments, which is why 2xx IDs rise by roughly 0.0625 in at larger sizes. The standard also defines the tolerances for ID and cross-section, which grow with size. Because tolerances are part of the callout, the nominal values listed here are not enough to check an inspection report.

Common mistakes

The two main mistakes are confusing inch and metric O-rings, and ordering by ID alone. A 25 mm ID metric ring is not the same as any dash size. A dash 210 (0.734 in ID, 0.139 in CS) is not interchangeable with a metric ring of similar ID but a different cross-section. Always carry both ID and cross-section into the ERP item description, along with the compound and durometer.

Using it with ERP item masters

Most shops store O-rings as stock items with a description like 'O-RING 2-210 FKM 75'. Standardising the dash number, material code and durometer in a fixed pattern makes the item master searchable and prevents duplicates. Add the cross-section and ID as attributes so engineers can filter. The chart's exportable Excel form works as a cleanup key for matching legacy descriptions to the correct size.

Frequently Asked Questions

What does AS568 dash number mean?

It is the size code for a standard inch-series O-ring. The number fixes the nominal inside diameter and the cross-section, and the series determines the section. For example dash 210 is 0.734 in ID by 0.139 in cross-section.

What is the size of an AS568-210 O-ring?

Nominal inside diameter is 0.734 inches and nominal cross-section is 0.139 inches, which gives an outside diameter of 1.012 inches. In millimetres that is about 18.64 mm ID by 3.53 mm cross-section.

Are AS568 O-rings the same as metric O-rings?

No. AS568 is an inch-based series with its own dash numbers. Metric O-rings follow ISO 3601 sizes and are specified by ID and cross-section in millimetres. Some sizes are close but not identical, so do not substitute without checking both dimensions.

Does this list every AS568 size?

No. It shows the common sizes in the 0xx to 3xx series as a quick lookup, and the full standard has many more, including the 4xx series. Check the current AS568 document or your supplier catalogue for the complete range and tolerances.

If your item master has hundreds of free-text O-ring descriptions, we can show how a private assistant normalises them to a dash number, compound and durometer without sending data off site.

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