Engineering Reference

O-Ring Size Chart

Reference dimensions for AS568 O-ring sizes, including inside diameter, cross section, and outside diameter. Useful for hydraulic, pneumatic, sealing, and general mechanical design.

Standard

AS568

O-Ring Geometry

Nominal ID · OD · Cross Section

Inside Diameter

The nominal inside diameter of the O-ring.

Cross Section

The nominal diameter of the O-ring cross section.

Applications

Hydraulic / Pneumatic

Suitable as a reference for static and dynamic sealing designs.

Standard

AS568

Aerospace Standard 568 dimensional identification system.

Dimensional Reference

AS568 O-Ring Size Table

Common AS568 dash numbers with nominal dimensions in inches and millimeters.

40 reference sizes

AS568 Size	Dash No.	Inside Diameter		Cross Section		Outside Diameter
AS568 Size	Dash No.	in	mm	in	mm	in	mm
001	-001	0.029	0.74	0.040	1.02	0.109	2.77
002	-002	0.042	1.07	0.040	1.02	0.122	3.10
003	-003	0.056	1.42	0.040	1.02	0.136	3.45
004	-004	0.070	1.78	0.040	1.02	0.150	3.81
005	-005	0.082	2.08	0.040	1.02	0.162	4.11
006	-006	0.103	2.62	0.040	1.02	0.183	4.65
007	-007	0.114	2.90	0.040	1.02	0.194	4.93
008	-008	0.145	3.68	0.040	1.02	0.225	5.72
009	-009	0.208	5.28	0.040	1.02	0.288	7.32
010	-010	0.239	6.07	0.040	1.02	0.319	8.10
011	-011	0.301	7.65	0.040	1.02	0.381	9.68
012	-012	0.362	9.19	0.040	1.02	0.442	11.23
013	-013	0.424	10.77	0.040	1.02	0.504	12.80
014	-014	0.487	12.37	0.040	1.02	0.567	14.40
015	-015	0.549	13.94	0.040	1.02	0.629	15.98
016	-016	0.612	15.54	0.040	1.02	0.692	17.58
017	-017	0.674	17.12	0.040	1.02	0.754	19.15
018	-018	0.737	18.72	0.040	1.02	0.817	20.75
019	-019	0.799	20.30	0.040	1.02	0.879	22.33
020	-020	0.862	21.89	0.040	1.02	0.942	23.93
021	-021	0.921	23.39	0.050	1.27	1.021	25.93
022	-022	1.039	26.39	0.050	1.27	1.139	28.93
023	-023	1.161	29.49	0.050	1.27	1.261	32.03
024	-024	1.299	33.00	0.050	1.27	1.399	35.53
025	-025	1.424	36.17	0.050	1.27	1.524	38.71
026	-026	1.549	39.34	0.050	1.27	1.649	41.88
027	-027	1.674	42.52	0.050	1.27	1.774	45.06
028	-028	1.799	45.69	0.050	1.27	1.899	48.23
029	-029	1.924	48.87	0.050	1.27	2.024	51.41
030	-030	2.049	52.04	0.050	1.27	2.149	54.58
031	-031	2.174	55.22	0.050	1.27	2.274	57.76
032	-032	2.299	58.39	0.050	1.27	2.399	60.93
033	-033	2.424	61.57	0.050	1.27	2.524	64.11
034	-034	2.549	64.74	0.050	1.27	2.649	67.29
035	-035	2.674	67.92	0.050	1.27	2.774	70.46
036	-036	2.799	71.09	0.050	1.27	2.899	73.63
037	-037	2.924	74.27	0.050	1.27	3.024	76.81
038	-038	3.049	77.44	0.050	1.27	3.149	79.73
039	-039	3.174	80.62	0.050	1.27	3.274	83.16
040	-040	3.299	83.79	0.050	1.27	3.399	86.33

Design Workflow

O-Ring Selection Guide

Determine the Bore or Shaft Diameter

Identify the nominal diameter of the piston, shaft, bore, or housing. The O-ring ID should be selected according to the intended sealing configuration.

Select the Cross Section

Choose the appropriate cross section based on groove geometry, pressure, tolerances, available space, and the required sealing performance.

Verify the Groove Design

O-ring selection is not based on diameter alone. Groove width, groove depth, squeeze, stretch, tolerances, and extrusion gap must also be evaluated.

Hydraulic Applications

High-pressure sealing

Hydraulic sealing designs should account for pressure, temperature, fluid compatibility, dynamic motion, squeeze, tolerances, and the risk of extrusion. Backup rings may be required in high-pressure applications.

Pneumatic Applications

Dynamic air sealing

Pneumatic applications typically require attention to low friction, leakage control, appropriate squeeze, lubrication, and stable O-ring movement within the groove.

Engineering Reference Note

AS568 dimensions should be treated as nominal reference values for O-ring identification and sizing. Actual sealing design should also consider elastomer material, temperature, pressure, media compatibility, squeeze, stretch, groove tolerances, surface finish, and extrusion gap. For critical applications, verify the final design against the applicable standard, manufacturer data, and application-specific requirements.