Free Engineering Tool
O-Ring Size Selection
Find the right standard O-ring size per ISO 3601 for piston, rod, or face seal applications. Get groove dimensions, squeeze percentage, and stretch — instantly.
Results
ISO 3601 Standard Cross-Sections
| CS (mm) | AS568 Series | CS Tolerance | Typical ID Range | Groove Depth (20% sq.) | Groove Width |
|---|---|---|---|---|---|
| 1.78 | -0XX | ±0.08 | 1–25 mm | 1.42 | 2.50 |
| 2.62 | -1XX | ±0.09 | 9–76 mm | 2.10 | 3.60 |
| 3.53 | -2XX | ±0.10 | 15–133 mm | 2.82 | 4.80 |
| 5.33 | -3XX | ±0.13 | 19–267 mm | 4.26 | 7.15 |
| 6.99 | -4XX | ±0.15 | 50–292 mm | 5.59 | 9.40 |
O-Ring Squeeze
Squeeze is the diametral compression of the O-ring cross-section when installed in the groove. It creates the initial seal contact stress.
- Dynamic seals (piston/rod): 10–20% squeeze recommended
- Static seals (face/flange): 15–30% squeeze recommended
Groove Dimensions
The groove width must allow the O-ring to expand laterally when squeezed, plus accommodate thermal expansion and swell.
Stretch & Compression
For piston seals, the O-ring is stretched over the piston. For rod seals, it is compressed into the bore groove.
- Max stretch: 5% (standard elastomers), 3% (PTFE, hard compounds)
- Max compression: 3% of ID
Target: O-ring OD ≈ bore = 50 mm
Required ID = 50 − 2 × 3.53 = 42.94 mm
Nearest standard ID: 42.86 mm → OD = 42.86 + 2 × 3.53 = 49.92 mm
Groove depth (20% squeeze) = 3.53 × 0.80 = 2.82 mm
Groove width = 3.53 × 1.35 = 4.77 mm
Groove bottom diameter* = 50 − 2 × 2.82 = 44.36 mm
Stretch = (44.36 − 42.86) / 42.86 × 100 ≈ 3.5% ✓ (within the 5% limit)
*assuming piston OD ≈ bore; subtract the piston-to-bore clearance from the piston OD for the exact groove bottom diameter
⚠️ Note: Always verify groove fill ratio (O-ring volume vs groove volume). The O-ring should fill 70–85% of the groove. Under-filling causes instability; over-filling prevents thermal expansion and causes extrusion.
ℹ️ Tip: For pressures above 3.5 MPa (static) or 7 MPa (dynamic), add a backup ring on the low-pressure side to prevent O-ring extrusion into the gap.
Professional field balancing instruments and software. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
