o-rings

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 extrusion at higher pressure. A softer O-ring may seal a rough or uneven surface better. The groove dimensions must still control squeeze and fill.

O-ring sealing is sensitive to surface finish. Sharp edges, scratches and excessive roughness can cut or twist the O-ring during assembly. The groove and mating surfaces should be cleaned before installation. Assembly lubrication with a compatible fluid or grease helps prevent surface damage.

Backup rings can be used when pressure is high or clearance is large. Backup ring installation is common in hydraulic cylinders and high pressure pumps. The backup ring is normally placed on the low pressure side of the O-ring.

O-Ring Applications

O-rings are used in static face seals, radial seals and low speed dynamic seals. Common locations include hydraulic fittings, pump covers, valve caps, flanges, filter housings, cylinder heads and instrumentation connectors. Dynamic O-ring seals require more careful material and groove design than static O-rings.

For rotating shaft seals at higher speed, oil seals or rotary shaft seals are usually a better choice than an O-ring. For hydraulic rod and piston sealing, hydraulic seals such as rod seals, piston seals and buffer seals handle load and wear better than a plain O-ring in many applications.

How to Specify an O-Ring for Quotation

To receive an O-ring quote, send the following information. Clear dimensions reduce repeated questions and help prevent ordering errors.

Inside diameter and cross section, or the standard size code.
Material and Shore A hardness, if known.
Operating temperature and pressure.
Fluid or gas medium.
Groove dimensions or assembly drawing, if available.
Required quantity and target packaging.

Send us the O-ring type, material, inside diameter, cross section, Shore A hardness, operating temperature, pressure, medium, groove dimensions, drawing or sample photo, and required quantity.

O-Ring Cord and O-Ring Kits

O-ring cord is used for maintenance and custom cutting where standard molded O-rings are not available or where large diameters are needed. CORASEALS can supply O-ring cord in different materials and cross sections. O-ring kits are used by repair teams and field service groups to keep common sizes available in one case.

For O-ring kits, buyers can request specific standard groups, size ranges or material-focused kits. A kit can be assembled based on equipment models or plant maintenance tasks.

FAQ

What O-ring standards does CORASEALS supply?

CORASEALS can supply O-rings in AS568, ISO 3601 and JIS B 2401 size systems. Custom molded O-ring sizes are also available for non-standard grooves.

Which O-ring material is suitable for hydraulic oil?

NBR and HNBR are common O-ring materials for mineral hydraulic oil. FKM is used when the oil temperature is higher or when chemical resistance is needed. The material choice depends on the hydraulic fluid type, temperature and pressure.

How do I measure an O-ring correctly?

Measure the inside diameter with an O-ring gauge or cone gauge. Measure the cross section with a caliper or micrometer. A used O-ring can swell or deform, so measure at several points and note the condition before selecting a replacement.

Can CORASEALS supply custom O-ring sizes?

Yes. CORASEALS can source custom molded O-rings for non-standard inside diameters, cross sections and materials. Send the groove dimensions or a sample O-ring for a quote.

What information should I send for an O-ring quote?

Send the inside diameter, cross section, material, Shore A hardness, operating temperature, pressure, fluid or gas medium, groove dimensions if available, and required quantity. Clear dimensions and operating conditions help produce a more accurate quote.

To request a quote for standard O-rings, custom O-ring sizes, O-ring cord or O-ring kits, send the inside diameter, cross section, material, Shore A hardness, operating temperature, pressure, fluid or gas medium, groove dimensions if available, and required quantity.