AS568-358

Standard Imperial O-Ring Size

Dimensions

Inside Diameter (inch)	3.950 in
Cross Section (inch)	0.139 in
Inside Diameter (mm)	100.33 mm
Cross Section (mm)	3.53 mm
Recommended Groove Depth	0.104 in
Theoretical Static Compression	25.2% (Target: 15-25%)

Quick Reference

ID: 3.950" (100.33 mm)

CS: 0.139" (3.53 mm)

Static Compression: 25.2%

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

Groove Depth: 0.104 in

Groove Width: 0.167 in (1.2× CS)

About This Size

AS568-358 is a AS568 300 Series imperial O-ring with 3.950" inside diameter (100.33 mm) and 0.139" cross section (3.53 mm). At the recommended groove depth of 0.104", theoretical static compression is 25.2% — 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 heavy machinery, large cylinders, process equipment.

Part of AS568 300 Series

Adjacent Sizes

AS568-357

Smaller ID (same cross section)

AS568-359

Larger ID (same cross section)

Cross-Standard Reference

Standard	Nearest Size	ID Δ	CS Δ
ISO 3601	100.00x3.55	0.33 mm	0.02 mm
JIS B 2401	P-3.50x100.00	0.33 mm	0.03 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

Large hydraulic assemblies
Supports heavy-duty cylinder heads, press platens, and mobile equipment covers at 100 mm nominal ID.
Pipeline & tank closures
Used on manway covers, valve bonnets, and static flange joints where groove width allows a robust cross section.

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 358?

AS568 300 Series covers dash 358 with a 0.139" (3.53 mm) cross section. Heavy machinery, large cylinders, process equipment

What extrusion gap is safe for this size?

For a 0.139" 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 AS568-358?

The closest ISO 3601 catalog size is 100.00x3.55 (ID 100.00 mm × CS 3.55 mm). ID differs by 0.33 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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