About O-Ring Groove Calculator (AS568 Static Glands)
The O-ring groove calculator turns a dash number into a machinable groove. Pick one of the scoped AS568 sizes — six representative dashes in each of the five standard cross-sections — or enter a custom cross-section and inside diameter, and the tool returns the industrial static radial gland from the Parker O-Ring Handbook Design Chart 4-1: gland depth, groove width (no back-up rings), groove radius, and the diametral clearance the extrusion gap must stay within. Every chart cell was verified against the published ORD 5700 handbook.
Around the verified gland the calculator computes the three percentages that decide whether the seal works: squeeze (from the cross-section tolerance extremes against the gland depth — it must land in the chart's printed band), gland fill (the O-ring may never occupy more than 90% of the groove volume; 60–85% with 75% optimum is the handbook range), and installed ID stretch on your groove diameter (at most 5%). Each carries a pass/fail badge decided at the displayed precision.
How It Works
- Select the O-ring. Dash mode covers 30 representative AS568 sizes: -0xx (0.070 in cross-section), -1xx (0.103), -2xx (0.139), -3xx (0.210), and -4xx (0.275). Custom mode accepts any cross-section within 8% of a standard class — metric near-equivalents like 1.78, 2.62, 3.53, 5.33 and 7.00 mm sections land in the right class automatically — plus the ring's inside diameter.
- Read the gland: depth L (the radial distance from the groove root to the mating surface), groove width G sized for no back-up rings, the maximum bottom radius, and the diametral clearance range. Machine the groove to these limits; surface finish per the handbook is 32 µin RMS on the sealing faces.
- Check squeeze: the tool recomputes the squeeze percentage at both cross-section tolerance extremes — a skinny ring in the deepest groove and a fat ring in the shallowest — and shows the chart's printed band alongside. Static radial seals want roughly 15–30% depending on section; the verified chart builds that in.
- Check gland fill: the ring's cross-sectional area divided by the groove's. The handbook calls for 60–85% fill (75% optimum) and at least a 10% void in any elastomer gland — the badge fails if the worst-case fat-ring / tight-groove combination exceeds 90%, because thermal expansion and fluid swell need somewhere to go.
- Check stretch: enter the groove (gland root) diameter and the tool computes the installed ID stretch. Up to 5% is acceptable per the handbook; more shortens seal life and thins the cross-section. Negative stretch (a compressed ID) means the ring will bunch and should be avoided — pick the next smaller dash instead.
Worked Example
Seal a 1-inch static piston with a -214 O-ring (0.139 in cross-section, 0.984 in ID). Design Chart 4-1 gives gland depth 0.111–0.113 in, groove width 0.187–0.192 in, radius 0.010–0.025 in, and diametral clearance 0.003–0.006 in. Squeeze across the W tolerance: (0.135 − 0.113)/0.135 = 16.3% up to (0.143 − 0.111)/0.143 = 22.4% — inside the printed 16–23% band. Gland fill: π/4 × 0.139² = 0.01517 in² of rubber in a 0.112 × 0.1895 = 0.02122 in² groove = 71.5% nominal (worst case 77.4%, comfortably under 90%). On a 1.004 in groove diameter the installed stretch is (1.004 − 0.984)/0.984 = 2.0% — inside the 5% limit.
Formulas
- Squeeze across the cross-section tolerance
squeeze% = (W − L) / W × 100, evaluated at W ± tol vs L max/min- Gland fill
fill% = (π/4 × W²) / (L × G) × 100- Installed stretch
stretch% = (D_groove − ID) / ID × 100
Standards & References
- Parker O-Ring Handbook ORD 5700 — Design Chart 4-1 (industrial O-ring static seal glands): gland depth, squeeze, groove width, radius, and diametral clearance per cross-section, verified against the published handbook
- Parker O-Ring Handbook ORD 5700, Table 9-1 — AS568A O-ring sizes (actual ID and W with tolerances) for the scoped dash list
- SAE AS568 — Aerospace Size Standard for O-rings, the dash-number system the size table reproduces
- ORD 5700 design guidance: gland fill 60–85% (75% optimum, ≥ 10% void essential); installed ID stretch not more than 5%
Frequently Asked Questions
What groove size do I machine for a -214 O-ring?
For a static radial (piston/bore) seal: groove depth 0.111–0.113 in and groove width 0.187–0.192 in with a bottom radius of 0.010–0.025 in, per Parker Design Chart 4-1 for the 0.139 in cross-section family (-201 through -284). Hold the diametral clearance to 0.003–0.006 in to control extrusion.
How much squeeze should a static O-ring have?
The verified industrial-gland chart delivers roughly 22–32% for 0.070 in cross-sections down to 15–20% for 0.275 in — smaller sections need proportionally more squeeze because tolerances eat a bigger share. If you machine to the chart's gland depth, the squeeze lands in the right band automatically; this calculator recomputes it from the tolerance extremes so you can see the actual range.
Why must gland fill stay below 90%?
Rubber is incompressible — it changes shape, not volume. The ring needs void space for thermal expansion and fluid swell; with less than about 10% void the gland becomes hydraulically locked and forces blow the ring into the clearance gap or split the groove corners. The handbook design range is 60–85% fill with 75% as the optimum.
How much stretch is acceptable on installation?
Per the Parker handbook, the ID stretch as installed in the groove should not exceed 5% — beyond that the cross-section thins measurably (reducing squeeze) and most compounds age faster under tension. A slight positive stretch keeps the ring seated in a male gland; if the calculator shows negative stretch the ring is compressed on its ID and will bunch — use the next smaller dash.
Does this tool cover face seals or dynamic glands?
No — the verified chart is the industrial STATIC radial gland (Design Chart 4-1). Face-seal (axial) glands use a different chart with squeeze set by groove depth alone, and dynamic reciprocating glands run much lighter squeeze; both are out of scope here. The dash dimensions themselves are the same in every application.
What about metric O-rings?
Custom mode accepts any cross-section within 8% of a standard class, which covers the common metric sections: 1.78 mm (0.070 in), 2.62 mm (0.103), 3.53 mm (0.139), 5.33 mm (0.210), and 7.00 mm (≈0.275). Enter the section and ID in inches (divide mm by 25.4) and the matching class gland applies. True metric gland standards like ISO 3601-2 differ in detail and are not encoded here.