Metric O-Rings
O-Rings & Rotary Seals · 7 specs
Direct Answer
Metric O-rings under ISO 3601-1 and DIN 3771 are designated directly by inside diameter (d_1) and cross-section cord diameter (d_2) in millimeters (e.g. 15.0 × 2.5 mm), matching standard metric groove depths and dynamic cylinder bores.
Source: ISO 3601-1:2012 Fluid Power Systems — O-Rings / DIN 3771 · Last reviewed Aug 28, 2026
Specs
| Governing Standards | ISO 3601-1 (Class A & B tolerances) / DIN 3771-1 |
| Callout Designation | [Inside Diameter d₁ in mm] × [Cross-Section d₂ in mm] (e.g. 20.0 × 3.0) |
| Standard Metric Cord Sizes (d₂) | 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 5.7, 6.0, 7.0, 8.0 mm |
| Micro / Miniature Metric Series | 0.5 mm to 1.2 mm cross-section for watch crowns and precision instruments |
| Static Gland Compression Ratio | 18% to 28% of cord diameter d₂ |
| Dynamic Gland Compression Ratio | 10% to 18% of cord diameter d₂ |
| Hardness Benchmark | 70 Shore A (General pneumatic/hydraulic) vs 90 Shore A (High pressure > 100 bar) |
Standard ISO 3601 Metric O-Ring Sizing Matrix
| Metric Size Callout (d_1 × d_2) | Inside Diameter (d_1) | Cross-Section Cord (d_2) | Static Radial Groove Depth (h) | Dynamic Radial Groove Depth (h) | Typical Metric Application |
|---|---|---|---|---|---|
| 6.0 × 1.5 mm | 6.0 mm | 1.5 mm | 1.15 mm | 1.30 mm | Pneumatic fittings, sensor housings |
| 10.0 × 2.0 mm | 10.0 mm | 2.0 mm | 1.50 mm | 1.70 mm | Small hydraulic valves, quick couplers |
| 15.0 × 2.5 mm | 15.0 mm | 2.5 mm | 1.90 mm | 2.15 mm | Automotive fuel injection rails, water pumps |
| 20.0 × 3.0 mm | 20.0 mm | 3.0 mm | 2.30 mm | 2.60 mm | Hydraulic cylinder pistons, pipe unions |
| 30.0 × 3.5 mm | 30.0 mm | 3.5 mm | 2.70 mm | 3.05 mm | Gearbox covers, coolant thermostat housings |
| 40.0 × 4.0 mm | 40.0 mm | 4.0 mm | 3.10 mm | 3.50 mm | Heavy machinery hydraulic rams |
| 50.0 × 5.0 mm | 50.0 mm | 5.0 mm | 3.90 mm | 4.40 mm | Flanged pipe joints, pressure vessels |
Material Chemical Compatibility Guide
Matching O-ring polymer compound to operating media is critical to prevent degradation:
- NBR (Nitrile / Buna-N): Petroleum oils, gasoline, hydraulic fluid (-30°C to +100°C). Attacked by ozone, weather, and brake fluid.
- FKM (Fluorocarbon / Viton): High temperatures (-20°C to +200°C), synthetic motor oils, aggressive fuels, acids, and ozone.
- EPDM (Ethylene Propylene): Glycol brake fluid (DOT 3/4/5.1), hot water/steam (+150°C). Instantly destroyed by petroleum mineral oils.
- VMQ (Silicone): Extreme thermal range (-60°C to +220°C), food/medical NSF-51. Low mechanical tear and abrasion resistance.