AS568-313
Standard Imperial O-Ring Size
Dimensions
| Inside Diameter (inch) | 0.662 in |
| Cross Section (inch) | 0.210 in |
| Inside Diameter (mm) | 16.81 mm |
| Cross Section (mm) | 5.33 mm |
| Recommended Groove Depth | 0.172 in |
| Theoretical Static Compression | 18.3% (Target: 15-25%) |
Quick Reference
About This Size
AS568-313 is a AS568 300 Series imperial O-ring with 0.662" inside diameter (16.81 mm) and 0.210" cross section (5.33 mm). At the recommended groove depth of 0.172", theoretical static compression is 18.3% — 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, heavy hydraulics, process equipment.
Part of AS568 300 Series
Adjacent Sizes
Cross-Standard Reference
| Standard | Nearest Size | ID Δ | CS Δ |
|---|---|---|---|
| ISO 3601 | 17.00x2.65 | 0.19 mm | 2.68 mm |
| JIS B 2401 | P-5.70x18.00 | 1.19 mm | 0.37 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 5.3 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.
- High-load static joints
The larger cross section tolerates wider extrusion gaps and higher bolt loads on flat-face flanges.
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 313?
AS568 300 Series covers dash 313 with a 0.210" (5.33 mm) cross section. Large flanges, heavy hydraulics, process 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 AS568-313?
The closest ISO 3601 catalog size is 17.00x2.65 (ID 17.00 mm × CS 2.65 mm). ID differs by 0.19 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