AS568 standard O-ring sizes with recommended groove width, depth, and radii for static face, static radial, dynamic piston, and dynamic rod seals. Includes metric BS / JIS equivalents and squeeze-percentage guidelines.
Updated Apr 24, 20262 min read
AS568 is the US aerospace / industrial standard for O-ring dimensions. It defines cross-section diameters in 5 sizes: 0.070", 0.103", 0.139", 0.210", and 0.275". Each size has dash-number ranges (e.g. -2xx are all 0.139" cross-section). Groove design targets a specific squeeze ratio — static face / radial uses 20-30% squeeze, dynamic reciprocating uses 8-20%, rotary uses 0-8%. This chart gives the groove width and depth for each scenario plus the recommended hardware dimensions.
AS568 standard cross-section sizes
Dash range
CS nominal
CS tolerance
Used for
−001 through −050
0.070" (1.78 mm)
±0.003"
Small bores, precision instruments
−102 through −178
0.103" (2.62 mm)
±0.003"
General purpose up to ~1.5" bore
−201 through −284
0.139" (3.53 mm)
±0.004"
General purpose, 1.5 - 10" bore
−309 through −395
0.210" (5.33 mm)
±0.005"
Larger bores, hydraulic cylinders
−425 through −475
0.275" (6.99 mm)
±0.006"
Very large bores, heavy hydraulics
Recommended groove dimensions by cross-section
CS
Static face groove W
Static face depth
Dynamic piston groove W
Dynamic piston depth
Dynamic rod groove W
Dynamic rod depth
0.070"
0.094-0.104"
0.050-0.057"
0.093-0.098"
0.055-0.057"
0.094-0.099"
0.055-0.057"
0.103"
0.138-0.146"
0.074-0.081"
0.140-0.144"
0.083-0.085"
0.141-0.144"
0.083-0.085"
0.139"
0.188-0.198"
0.101-0.108"
0.187-0.190"
0.113-0.115"
0.188-0.190"
0.113-0.115"
0.210"
0.281-0.290"
0.152-0.163"
0.281-0.284"
0.170-0.173"
0.281-0.284"
0.170-0.173"
0.275"
0.375-0.387"
0.201-0.213"
0.375-0.379"
0.224-0.228"
0.375-0.379"
0.224-0.228"
Squeeze percentage guidelines
Static face seal (gland against flat)
20-30% squeeze. Groove depth = CS × 0.70-0.80.
Static radial (inside a bore or on OD)
15-25% squeeze. Groove depth = CS × 0.75-0.85.
Dynamic reciprocating (piston / rod)
8-16% squeeze. Too much squeeze → seal rolls and wears.
Rotary (shaft seal)
0-8% squeeze. Too much heat from friction destroys nitrile; consider X-ring or rotary seal instead.
Vacuum
20-30% squeeze + low-outgassing compound (FFKM or VMQ).
Groove stretch & compression rules
ID stretch
Max 5% for long life; 2% is ideal. > 5% stretch accelerates aging.
OD compression
Max 3% compression (free vs installed OD).
Groove fill
60-85% of groove volume. Too much fill → extrusion; too little → loss of sealing force.
Back-up rings
Add for pressures > 1500 psi on dynamic seals or > 3000 psi static.
Surface finish groove
32 Ra μin max static; 16 Ra μin for dynamic seals. Lay perpendicular to seal motion.
Common AS568 sizes (most-stocked static)
Dash #
ID (in)
OD (in)
CS (in)
-004
0.070
0.210
0.070
-008
0.171
0.311
0.070
-014
0.489
0.629
0.070
-018
0.739
0.879
0.070
-022
1.114
1.254
0.070
-112
0.487
0.693
0.103
-115
0.612
0.818
0.103
-118
0.862
1.068
0.103
-122
1.114
1.320
0.103
-210
0.734
1.012
0.139
-214
0.984
1.262
0.139
-218
1.234
1.512
0.139
-222
1.484
1.762
0.139
-226
2.239
2.517
0.139
-230
2.614
2.892
0.139
-232
2.864
3.142
0.139
-236
3.239
3.517
0.139
-240
3.734
4.012
0.139
-244
4.234
4.512
0.139
-326
2.000
2.420
0.210
-328
2.125
2.545
0.210
-334
2.750
3.170
0.210
-338
3.125
3.545
0.210
-342
3.625
4.045
0.210
-346
4.125
4.545
0.210
Metric / JIS equivalents
ISO 3601 / BS1806
European standard. Sizes partially overlap AS568 but use metric IDs.
JIS B 2401 P-series
Japanese reciprocating / static seal (e.g. P-10 = 9.8 × 2.4 mm).
−40 to +250°F. Oil, grease, hydraulic fluid, water. Cheapest general-purpose. Poor in ozone / sun.
Viton (FKM)
−20 to +400°F. Fuels, oils, most solvents. Not for hot water / steam / ketones / amines.
EPDM
−60 to +300°F. Hot water, steam, brake fluid, mild acids/bases. Fails immediately in petroleum oils.
Silicone (VMQ)
−100 to +450°F. Food-grade, inert. Poor abrasion resistance; not for dynamic seals.
Kalrez / FFKM
−20 to +600°F. Nearly universal chemical resistance. $$$$ — use only when nothing else works.
Polyurethane (AU / EU)
−40 to +200°F. Excellent abrasion resistance for dynamic seals. Hydrolysis in hot water.
Notes
Dimensions from SAE AS568 and Parker Handbook ORD 5712. Always cross-check against the seal manufacturer's gland-design spec for your specific application (dynamic rate, temperature, media, pressure).
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