AS568-121

Standard Imperial O-Ring Size

Dimensions

Inside Diameter (inch)	1.049 in
Cross Section (inch)	0.103 in
Inside Diameter (mm)	26.64 mm
Cross Section (mm)	2.62 mm
Recommended Groove Depth	0.082 in
Theoretical Static Compression	20.4% (Target: 15-25%)

Quick Reference

ID: 1.049" (26.64 mm)

CS: 0.103" (2.62 mm)

Static Compression: 20.4%

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

Groove Depth: 0.082 in

Groove Width: 0.124 in (1.2× CS)

About This Size

AS568-121 is a AS568 100 Series imperial O-ring with 1.049" inside diameter (26.64 mm) and 0.103" cross section (2.62 mm). At the recommended groove depth of 0.082", theoretical static compression is 20.4% — within the typical 15–25% target for static glands. This dash number is widely stocked in NBR, FKM, EPDM, VMQ, and PTFE for hydraulics, pneumatics, automotive, general industrial.

Part of AS568 100 Series

Adjacent Sizes

AS568-120

Smaller ID (same cross section)

AS568-122

Larger ID (same cross section)

Cross-Standard Reference

Standard	Nearest Size	ID Δ	CS Δ
ISO 3601	26.50x2.65	0.14 mm	0.03 mm
JIS B 2401	P-2.40x26.50	0.14 mm	0.22 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

Hydraulic & pneumatic fittings
Used in adapter threads, quick couplings, and valve spools where 2.6 mm cross section balances conformability and pressure rating.
Automotive fuel & emissions
Typical in fuel injectors, EVAP valves, and small pump housings on North American and European platforms.

Tolerance & Standard Notes

AS568 defines a single tolerance table that applies to every dash number (the two-class system of the 1971 issue was merged in AS568A). For critical dynamic seals, tighter-than-standard dimensional tolerances agreed with the manufacturer (per drawing) are the standard route; surface quality is specified separately under ISO 3601-3 grades N, S, or CS.

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

Design FAQ

What AS568 series is dash 121?

AS568 100 Series covers dash 121 with a 0.103" (2.62 mm) cross section. Hydraulics, pneumatics, automotive, general industrial

What extrusion gap is safe for this size?

For a 0.103" 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 AS568-121?

The closest ISO 3601 catalog size is 26.50x2.65 (ID 26.50 mm × CS 2.65 mm). ID differs by 0.14 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.

Request AS568 PDF