AS568 O-Ring Sizes
O-Rings & Rotary Seals · 10 specs
Direct Answer
Aerospace Standard AS568 (SAE AS568 / ISO 3601-1) classifies inch-series elastomeric O-rings into five cross-section diameter series: 000 (1/16" / 1.78 mm), 100 (3/32" / 2.62 mm), 200 (1/8" / 3.53 mm), 300 (3/16" / 5.33 mm), and 400 (1/4" / 6.99 mm).
Source: SAE AS568D Standard Size Catalog for O-Rings / ISO 3601-1 · Last reviewed Aug 28, 2026
Specs
| Governing Standards | SAE AS568D / ISO 3601-1 Class A / MIL-STD-120 |
| 000 Series Cross-Section (1/16") | CS: 0.070 in ± 0.003 in (1.78 mm ± 0.08 mm) | Dash -001 to -050 |
| 100 Series Cross-Section (3/32") | CS: 0.103 in ± 0.003 in (2.62 mm ± 0.08 mm) | Dash -102 to -178 |
| 200 Series Cross-Section (1/8") | CS: 0.139 in ± 0.004 in (3.53 mm ± 0.10 mm) | Dash -201 to -284 |
| 300 Series Cross-Section (3/16") | CS: 0.210 in ± 0.005 in (5.33 mm ± 0.13 mm) | Dash -309 to -395 |
| 400 Series Cross-Section (1/4") | CS: 0.275 in ± 0.006 in (6.99 mm ± 0.15 mm) | Dash -425 to -475 |
| 900 Series (Straight Thread Tube Fitting) | Boss seals for SAE J1926/MS33649 (Dash -901 to -932) |
| Standard Static Gland Squeeze | 15% to 30% radial or axial compression |
| Standard Dynamic Gland Squeeze | 10% to 20% radial compression (reduces friction and seal wear) |
| Common Elastomer Polymers | NBR (Buna-N 70/90A), FKM (Viton), EPDM, Silicone (VMQ), FFKM (Kalrez) |
Popular AS568 Standard O-Ring Dash Size Matrix
| AS568 Dash Number | Nominal Fraction (ID × OD × CS) | Actual Inner Diameter (ID) | Actual Cross-Section (CS) | Metric Inner Dia (ID) | Metric Cross-Section (CS) |
|---|---|---|---|---|---|
| -010 | 1/4" × 3/8" × 1/16" | 0.239" (±0.005) | 0.070" (±0.003) | 6.07 mm | 1.78 mm |
| -011 | 5/16" × 7/16" × 1/16" | 0.301" (±0.005) | 0.070" (±0.003) | 7.65 mm | 1.78 mm |
| -012 | 3/8" × 1/2" × 1/16" | 0.364" (±0.005) | 0.070" (±0.003) | 9.25 mm | 1.78 mm |
| -110 | 3/8" × 9/16" × 3/32" | 0.362" (±0.005) | 0.103" (±0.003) | 9.19 mm | 2.62 mm |
| -111 | 7/16" × 5/8" × 3/32" | 0.424" (±0.005) | 0.103" (±0.003) | 10.77 mm | 2.62 mm |
| -112 | 1/2" × 11/16" × 3/32" | 0.487" (±0.005) | 0.103" (±0.003) | 12.37 mm | 2.62 mm |
| -210 | 3/4" × 1" × 1/8" | 0.734" (±0.006) | 0.139" (±0.004) | 18.64 mm | 3.53 mm |
| -214 | 1" × 1-1/4" × 1/8" | 0.984" (±0.007) | 0.139" (±0.004) | 24.99 mm | 3.53 mm |
| -325 | 1-1/2" × 1-7/8" × 3/16" | 1.475" (±0.015) | 0.210" (±0.005) | 37.47 mm | 5.33 mm |
| -425 | 4-1/2" × 5" × 1/4" | 4.475" (±0.030) | 0.275" (±0.006) | 113.67 mm | 6.99 mm |
Gland Design & The 70-85% Groove Fill Rule
Elastomeric O-rings are essentially non-compressible fluids with high Poisson ratios:
- Volumetric Expansion (Groove Fill): An O-ring groove gland must never be designed to fit the ring with 100% fill. Under high temperature and chemical fluid absorption (oil/fuel swelling), an elastomer expands. Standard gland volume should equal 70% to 85% of the O-ring volume to leave thermal expansion clearance.
- Extrusion Gap & Backup Rings: Under high system pressure (>1,500 psi / 100 bar), differential pressure forces rubber into the diametral clearance gap between mating parts, nibbling the seal. Harder Durometer elastomers (90 Shore A) or PTFE backup rings must be installed behind the O-ring.