AS568-272
Standard Imperial O-Ring Size
Dimensions
| Inside Diameter (inch) | 4.644 in |
| Cross Section (inch) | 0.103 in |
| Inside Diameter (mm) | 117.96 mm |
| Cross Section (mm) | 2.62 mm |
| Recommended Groove Depth | 0.077 in |
| Theoretical Static Compression | 25.2% (Target: 15-25%) |
Quick Reference
Compression Rate Guidance
- Static seals: 15-25% compression is ideal for most 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: 16-32 microin Ra for static, 8-16 microin Ra for dynamic.
Common Applications
- Hydraulic & Pneumatic: Cylinder heads, valve bodies, pump housings.
- Automotive: Fuel injectors, oil filters, transmission pans.
- Industrial: Pipe flanges, equipment covers, sensor housings.
- Food & Pharma: Process vessel lids, filter housings, dispensing equipment.
Verify the specific size against your groove drawing before ordering. For non-standard grooves, use the Compression Calculator.
ISO & Tolerance Reference
AS568 sizes are defined in inches. The nearest ISO 3601-1 metric equivalent may differ in inside diameter even when the cross section matches closely. Always verify both ID and CS when substituting between standards.
Tolerances: AS568 Class 1 (standard commercial) tolerances apply unless Class 2 is specified. For critical applications, consider ISO 3601-1 Grade S or CS precision tolerances.
For tolerance details, see the O-Ring Tolerance Guide.
Design FAQ
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 — it increases friction and reduces conformability.
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 and prevent the O-ring from extruding into the clearance gap under pressure.
What surface finish is required?
For static seals: Ra 0.8–3.2 µm (32–125 µin). For dynamic reciprocating seals: Ra 0.4–0.8 µm (16–32 µin). For rotary seals: Ra 0.2–0.4 µm (8–16 µin). Rougher surfaces increase leak risk and accelerate wear.
Related Resources
Imperial Size Chart
Browse the full AS568 table when you need adjacent dash numbers or series comparisons.
View AS568 chartSize Converter
Convert this imperial size to metric equivalents before choosing ISO or JIS alternatives.
Open size converterCompression Calculator
Check gland squeeze and confirm whether your groove depth matches the target compression range.
Calculate compressionAS568 PDF Download
Request the printable size chart for engineering review, quoting, or shop-floor reference.
Request AS568 PDF