AS568-026

Standard Imperial O-Ring Size

Dimensions

Inside Diameter (inch)	1.239 in
Cross Section (inch)	0.040 in
Inside Diameter (mm)	31.47 mm
Cross Section (mm)	1.02 mm
Recommended Groove Depth	0.030 in
Theoretical Static Compression	25.0% (Target: 15-25%)

Quick Reference

ID: 1.239" (31.47 mm)

CS: 0.040" (1.02 mm)

Static Compression: 25.0%

Target Range: 15–25% static, 10–20% dynamic

Groove Depth: 0.030 in

Groove Width: 0.048 in (1.2× CS)

About This Size

AS568-026 is a AS568 100 Series imperial O-ring with 1.239" inside diameter (31.47 mm) and 0.040" cross section (1.02 mm). At the recommended groove depth of 0.030", theoretical static compression is 25.0% — above the usual static range; verify gland width and material swell. This dash number is widely stocked in NBR, FKM, EPDM, VMQ, and PTFE for aerospace, miniature fittings, instrumentation.

Part of AS568 100 Series

Adjacent Sizes

AS568-025

Smaller ID (same cross section)

AS568-027

Larger ID (same cross section)

Cross-Standard Reference

Standard	Nearest Size	ID Δ	CS Δ
ISO 3601	31.50x1.80	0.03 mm	0.78 mm
JIS B 2401	P-1.90x31.50	0.03 mm	0.88 mm

Cross-reference values are catalog nearest matches — always verify groove width, depth, and tolerance class on your drawing before substituting standards.

Compression Rate Guidance

Static seals: 15–25% compression is ideal for most fixed applications.
Dynamic seals: 10–20% compression to reduce friction and wear.
Groove width should typically be 1.1 to 1.3 times the O-ring cross section.
Surface finish: Ra 0.8–3.2 µm for static, Ra 0.4–0.8 µm for reciprocating dynamic service.

Typical Applications

Cylinder & pump sealing
Well suited to cylinder end caps, gear pump covers, and actuator bodies in the 31 mm bore range.
Industrial process equipment
Found on filter housings, dispensing heads, and medium-pressure flange joints in food, pharma, and chemical service.
Low-profile grooves
The thin cross section fits shallow glands in compact assemblies; verify extrusion gap carefully above 70 bar.

Tolerance & Standard Notes

AS568 Class 1 (standard commercial) tolerances apply unless Class 2 is specified. For critical dynamic seals, consider tighter ISO 3601 Grade S or CS tolerances on the metric substitute.

For tolerance details, see the O-Ring Tolerance Guide.

Design FAQ

What AS568 series is dash 026?

AS568 100 Series covers dash 026 with a 0.040" (1.02 mm) cross section. Aerospace, miniature fittings, instrumentation

What extrusion gap is safe for this size?

For a 0.040" cross section, limit the diametral extrusion gap to 0.004–0.006" (0.10–0.15 mm) for pressures up to 150 bar. Above 150 bar, use a PTFE backup ring regardless of gap size.

What hardness should I specify?

70 Shore A is the standard for most static and dynamic applications up to 100 bar. Use 80 Shore A for 100–200 bar dynamic service. Use 90 Shore A only for extreme extrusion resistance or abrasive conditions.

What is the nearest ISO 3601 metric equivalent to AS568-026?

The closest ISO 3601 catalog size is 31.50x1.80 (ID 31.50 mm × CS 1.80 mm). ID differs by 0.03 mm — verify groove dimensions before substituting.

When do I need a backup ring?

Use a backup ring when pressure exceeds 1,500 psi (100 bar) or when the extrusion gap is larger than 0.15 mm for this cross section. PTFE backup rings are standard for AS568 sizes.

Related Resources

Imperial Size Chart

Browse the full AS568 table when you need adjacent dash numbers or series comparisons.

View AS568 chart

Size Converter

Convert this imperial size to metric equivalents before choosing ISO or JIS alternatives.

Open size converter

Compression Calculator

Check gland squeeze and confirm whether your groove depth matches the target compression range.

Calculate compression

AS568 PDF Download

Request the printable size chart for engineering review, quoting, or shop-floor reference.

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