AS568-474
Standard Imperial O-Ring Size
Dimensions
| Inside Diameter (inch) | 25.888 in |
| Cross Section (inch) | 0.210 in |
| Inside Diameter (mm) | 657.56 mm |
| Cross Section (mm) | 5.33 mm |
| Recommended Groove Depth | 0.158 in |
| Theoretical Static Compression | 24.8% (Target: 15-25%) |
Quick Reference
About This Size
AS568-474 is a AS568 400 Series imperial O-ring with 25.888" inside diameter (657.56 mm) and 0.210" cross section (5.33 mm). At the recommended groove depth of 0.158", theoretical static compression is 24.8% — within the typical 15–25% target for static glands. This dash number is widely stocked in NBR, FKM, EPDM, VMQ, and PTFE for large flanges, pipelines, construction equipment.
Part of AS568 400 Series
Adjacent Sizes
Cross-Standard Reference
| Standard | Nearest Size | ID Δ | CS Δ |
|---|---|---|---|
| ISO 3601 | 250.00x2.65 | 407.56 mm | 2.68 mm |
| JIS B 2401 | P-8.40x500.00 | 157.56 mm | 3.07 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 static flange seals
At 658 mm ID, this size serves tank lids, heat exchanger covers, and large-bore pipeline flanges.
- Construction & mining equipment
Common on excavator cylinders, crusher housings, and other high-load static joints with generous gland geometry.
- High-load static joints
The larger cross section tolerates wider extrusion gaps and higher bolt loads on flat-face flanges.
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 474?
AS568 400 Series covers dash 474 with a 0.210" (5.33 mm) cross section. Large flanges, pipelines, construction equipment
What extrusion gap is safe for this size?
For a 0.210" 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 AS568-474?
The closest ISO 3601 catalog size is 250.00x2.65 (ID 250.00 mm × CS 2.65 mm). ID differs by 407.56 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 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