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O-Rings, Materials, Sizes and Selection for Industrial Sealing
Quick Answer: An O-ring is a round elastomer seal that fits in a groove and blocks fluid or gas leakage. CORASEALS supplies standard and custom O-rings in AS568, ISO 3601, JIS B 2401 and metric sizes. For a quote, send the inside diameter, cross section, material, hardness, temperature, pressure, medium and quantity.
CORASEALS supplies O-rings for static and low speed dynamic sealing in hydraulic systems, pumps, valves, flanges, filters, cylinders and process equipment. The O-ring range includes NBR, HNBR, FKM, EPDM, VMQ, FFKM, silicone, PTFE and other engineered materials. Standard sizes are available together with custom molded options, O-ring cord and O-ring kits.
Correct O-ring selection depends on more than the inside diameter and cross section. The material must resist the fluid or gas. The groove must provide the right squeeze. The surface finish must be smooth enough for a reliable seal. Temperature, pressure and assembly conditions also influence the final choice.
O-Ring Sizes and Standards
CORASEALS supports the main industrial O-ring size systems. AS568 covers inch sizes used in North America. ISO 3601 covers metric sizes for general industrial use. JIS B 2401 covers metric sizes common in Japanese equipment. The O-ring size is defined by inside diameter and cross section. For an AS568 size, the dash number refers to a specific size in the standard chart, but the actual ID and cross section should always be confirmed.
- AS568: inch O-ring sizes with standard dash numbers.
- ISO 3601: metric O-ring sizes for general industrial use.
- JIS B 2401: metric O-ring sizes for equipment designed in Japan.
- Custom sizes: molded O-rings for non-standard grooves and replacement requirements.
When comparing O-ring sizes, confirm the inside diameter and cross section in the same unit system. Do not replace a metric O-ring with an inch O-ring based only on a similar dash number.
O-Ring Material Selection
The O-ring material must match the fluid, temperature range and mechanical load. A material that works in hydraulic oil may fail in steam or aggressive solvents. CORASEALS helps buyers confirm the material before quotation.
| Material | Common Uses | Common Limitations |
|---|---|---|
| NBR | Mineral oil, hydraulic fluid, water, air and general service | Poor resistance to ozone, weather exposure and some polar solvents |
| HNBR | Hot oil, some refrigerants, water and abrasion resistant service | Higher cost than NBR and limited against strong polar solvents |
| FKM | High temperature oil, fuel, many chemicals and demanding hydraulic systems | Usually not recommended for steam, hot water or certain ketones |
| EPDM | Water, steam, brake fluids and weather exposed applications | Not suitable for mineral oil and most petroleum based systems |
| VMQ | Low temperature sealing, dry heat and food contact where approved compounds exist | Lower tear strength and not recommended for many oil and fuel seals |
| FFKM | Aggressive chemicals, high temperature hydrocarbon service and severe process conditions | High cost and usually reserved for applications where lower cost elastomers fail |
Material data varies by compound. The final material choice should be confirmed with a specific compound datasheet, not by the polymer name alone.
O-Ring Hardness and Groove Conditions
Common O-ring hardness values include 70 Shore A and 90 Shore A. Hardness selection depends on pressure, groove clearance and surface finish. A harder O-ring may resist extru