NBR O-Rings

NBR O-Rings - Nitrile O-Rings 70 Shore A

NBR O-rings are elastomeric sealing rings manufactured from Nitrile Butadiene Rubber, also known as nitrile rubber or Buna-N. NBR is widely used for O-rings in applications involving compatible mineral oils, lubricating greases, many fuels, hydraulic fluids and pneumatic systems. A common hardness for general-purpose NBR O-rings is 70 Shore A.

At simmering.pl, NBR O-rings are available in a wide range of metric sizes and can be selected primarily by inside diameter ID (d1) and cross-section CS (d2). Correct O-ring selection should also consider hardness, operating medium, temperature, pressure, groove geometry and whether the seal operates under static or dynamic conditions.

What is an NBR O-ring?

An NBR O-ring is a closed elastomeric sealing ring with a circular cross-section, manufactured from Nitrile Butadiene Rubber.

The abbreviation NBR stands for:

Nitrile Butadiene Rubber

Other commonly used names include:

• nitrile rubber
• Buna-N
• nitrile O-ring
• NBR sealing ring
• NBR rubber seal
• oil-resistant O-ring

NBR is one of the most widely used elastomer families in industrial sealing technology because appropriately selected compounds combine useful mechanical properties with resistance to many mineral oils, greases, fuels and hydraulic fluids.

The exact properties of an NBR O-ring depend on the formulation of the specific rubber compound, including its acrylonitrile content.

NBR O-Rings - key technical information

Temperature limits, chemical compatibility, pressure capability and service life must always be evaluated for the specific NBR compound and actual operating conditions.

How does an NBR O-ring work?

An O-ring is installed in a correctly dimensioned sealing groove between mating components.

During assembly, the O-ring is compressed. Elastic deformation of the rubber generates contact pressure against the mating surfaces, creating a sealing barrier.

Effective sealing depends on more than the O-ring material itself.

Important factors include:

• O-ring inside diameter
• O-ring cross-section
• groove dimensions
• compression
• O-ring stretch
• operating pressure
• operating temperature
• medium
• surface finish
• static or dynamic operation

Correct O-ring selection therefore requires consideration of size, material, hardness and operating conditions.

How are O-ring sizes specified?

The two fundamental dimensions of an O-ring are:

ID (d1) - inside diameter

and

CS (d2) - cross-section diameter.

For example:

NBR O-Ring 20x3 mm 70 ShA

means:

• inside diameter ID: 20 mm
• cross-section CS: 3 mm
• material: NBR
• nominal hardness: 70 Shore A

The calculated outside diameter is:

20 mm + 2 x 3 mm = 26 mm

Therefore, an O-ring size such as 20x3 mm normally refers to:

inside diameter x cross-section

and not outside diameter x width.

ID, CS, d1 and d2 - what do they mean?

Different technical documents, drawings and online catalogues may use different symbols for the same fundamental O-ring dimensions.

ID - Inside Diameter

CS - Cross Section

d1 - inside diameter

d2 - cross-section diameter

Understanding these parameters is essential when selecting a replacement O-ring from technical documentation, an existing seal or groove dimensions.

What does NBR mean?

NBR stands for Nitrile Butadiene Rubber, an elastomer produced from acrylonitrile and butadiene.

The balance between these components influences important material characteristics.

Therefore, not every NBR compound has identical:

• oil resistance
• fuel resistance
• low-temperature flexibility
• mechanical properties
• compression-set behaviour
• operating temperature range

This is why the material designation NBR identifies an elastomer family rather than one universal rubber formulation.

NBR O-Rings 70 Shore A

A very common hardness for general-purpose NBR O-rings is:

70 Shore A

This may also be written as:

• NBR 70 ShA
• NBR 70A
• NBR 70 Shore
• NBR 70 Shore A
• Buna-N 70A

Shore A hardness describes the hardness of an elastomer.

It influences how an O-ring deforms under compression, but hardness alone does not define all operating properties.

Two NBR 70 Shore A compounds may differ in:

• formulation
• acrylonitrile content
• low-temperature performance
• chemical resistance
• compression set
• mechanical properties
• regulatory approvals

Therefore, NBR 70 ShA should be considered an important material parameter, but not a complete compound specification.

NBR O-ring temperature range

There is no single temperature range that can safely be assigned to every NBR O-ring.

Temperature capability depends on the specific NBR compound, operating medium and service conditions.

For standard NBR compounds used in industrial sealing, continuous operation up to approximately +100°C is common, while exposure to higher temperatures can significantly reduce elastomer service life.

Low-temperature capability also varies according to the formulation.

For temperature-critical applications, always verify the technical data for the exact NBR compound rather than selecting an O-ring solely from the generic NBR material designation.

Are NBR O-rings oil resistant?

NBR is one of the principal elastomer families used for sealing many mineral oils and lubricating greases.

This is a major reason for the widespread use of nitrile O-rings in:

• hydraulic equipment
• pneumatic equipment
• industrial machinery
• mechanical assemblies
• lubrication systems
• pumps
• valves
• gearboxes
• maintenance and repair applications

However, the term oil-resistant O-ring should not be interpreted as resistance to every oil or industrial fluid.

Compatibility depends on:

• exact fluid composition
• NBR compound
• temperature
• pressure
• exposure time

For critical applications, the exact medium must be checked against the specific elastomer compound.

Are NBR O-rings fuel resistant?

NBR compounds are frequently used with fuels and aliphatic hydrocarbons.

However, fuel resistance varies according to the NBR formulation, particularly its acrylonitrile content, as well as the composition of the fuel itself.

Do not assume that every nitrile O-ring is suitable for every:

• petrol or gasoline formulation
• diesel fuel
• biofuel
• fuel blend
• hydrocarbon mixture

Critical fuel applications require compatibility verification for the exact NBR compound and operating conditions.

What is NBR not resistant to?

NBR is not a universal sealing material.

Standard nitrile rubber compounds generally have limitations when exposed to conditions such as:

• ozone
• prolonged UV radiation
• long-term outdoor weathering
• certain solvents
• selected aggressive chemicals
• some brake fluids
• temperatures exceeding the capability of the particular compound

For these environments, another elastomer such as EPDM, FKM, HNBR, VMQ or another application-specific sealing material may be more appropriate.

Material selection should always be based on the actual operating conditions.

NBR vs FKM O-rings

NBR and FKM are different elastomer families.

NBR O-rings are widely used with compatible mineral oils, greases, hydraulic fluids and many standard industrial applications.

FKM O-rings have a different chemical and thermal resistance profile and are often considered where the operating conditions exceed the capabilities of the selected NBR compound.

This does not mean that FKM is automatically the correct replacement for NBR.

Before changing material, compare:

• operating medium
• temperature
• pressure
• sealing-system design
• dynamic or static operation
• required service life

An NBR O-ring and FKM O-ring with identical dimensions are not automatically interchangeable.

NBR vs EPDM O-rings

NBR and EPDM have significantly different chemical compatibility profiles.

NBR is commonly selected for applications involving many mineral oils and greases.

EPDM is used with different groups of media and environmental conditions, depending on the specific compound.

The choice between NBR and EPDM should therefore begin with the operating medium, not simply price or temperature.

An EPDM O-ring should not automatically replace an NBR O-ring of the same size.

NBR vs VMQ silicone O-rings

VMQ is silicone rubber and has a different operating profile from NBR.

An NBR O-ring and a VMQ silicone O-ring may have identical dimensions and fit the same groove, but dimensional compatibility does not mean material equivalence.

When comparing NBR with VMQ, consider:

• operating medium
• temperature
• mechanical requirements
• environmental conditions
• static or dynamic operation
• expected service conditions

NBR vs HNBR O-rings

HNBR stands for Hydrogenated Nitrile Butadiene Rubber.

Although HNBR is chemically related to NBR, it is a separate elastomer family with a different performance profile.

NBR and HNBR O-rings of the same dimensions should not be treated as automatically interchangeable.

The correct material should be selected according to the specific medium, temperature, mechanical requirements and service conditions.

NBR O-rings for hydraulic systems

NBR is widely used in hydraulic sealing systems where the selected compound is compatible with the hydraulic fluid.

Applications may include sealing points in:

• hydraulic connections
• valve bodies
• control valves
• manifolds
• pumps
• hydraulic cylinders
• fittings
• industrial hydraulic equipment

At elevated pressure, additional factors become important, particularly extrusion clearance.

Depending on the sealing design, a back-up ring may be required to reduce the risk of elastomer extrusion.

A single universal maximum pressure should therefore not be assigned to all NBR O-rings.

NBR O-rings for pneumatic systems

NBR O-rings are also widely used in pneumatic equipment.

Selection should consider:

• pressure
• temperature
• lubrication
• movement speed
• surface condition
• static or dynamic operation
• friction requirements

A static pneumatic seal and a dynamically moving pneumatic seal may require different groove geometry and operating parameters.

Static vs dynamic O-ring seals

In a static O-ring seal, the mating components do not continuously move relative to each other during normal operation.

In a dynamic O-ring seal, relative movement occurs.

This may include reciprocating or rotary movement, depending on the application.

Dynamic sealing introduces additional considerations such as:

• friction
• lubrication
• speed
• heat generated by movement
• surface finish
• wear
• groove geometry

An O-ring suitable for a static application should not automatically be assumed to be suitable for demanding dynamic service.

How to choose the correct NBR O-ring

Correct O-ring selection should begin with the operating conditions.

Check:

1. inside diameter ID
2. cross-section CS
3. NBR material
4. required Shore A hardness
5. operating medium
6. minimum operating temperature
7. maximum operating temperature
8. pressure
9. static or dynamic operation
10. groove dimensions
11. mating-surface condition
12. required standards or approvals

Only after these parameters are known can the suitability of a specific O-ring be properly evaluated.

How to measure an O-ring

If the original O-ring designation is unknown, measure primarily:

Inside Diameter - ID

and

Cross Section - CS

For small O-rings, a difference of only a few tenths of a millimetre may be significant.

For example:

20x2 mm

is not the same size as:

20x2.5 mm

even though both have the same 20 mm inside diameter.

If an old O-ring is worn, flattened, stretched or swollen, its measured dimensions may differ from the original nominal dimensions.

In this situation, groove dimensions or equipment documentation should also be checked.

How to calculate O-ring outside diameter

When the inside diameter and cross-section are known, the theoretical outside diameter can be calculated as:

OD = ID + 2 x CS

Example:

For an O-ring measuring 25x3 mm:

• ID: 25 mm
• CS: 3 mm

Calculated outside diameter:

25 mm + 2 x 3 mm = 31 mm

This calculation can be useful when identifying an unknown sealing ring, but the nominal product size should still be based on ID and CS.

ISO 3601 and O-ring dimensions

The ISO 3601 series covers O-rings for fluid power systems and general industrial applications.

ISO 3601-1 defines fundamental aspects including:

• inside diameters
• cross-section diameters
• tolerances
• designation codes

This makes ID and CS key entities when identifying and selecting O-rings.

However, the existence of the ISO 3601 standard does not mean that every commercially available O-ring automatically complies with a specific ISO dimensional or quality class.

Where ISO compliance is required, it should be confirmed for the exact product.

Is every black O-ring made from NBR?

No.

Colour alone is not a reliable method of identifying an O-ring material.

A black O-ring may be manufactured from NBR, but other elastomers can also be black.

Material should be identified using:

• product documentation
• material designation
• manufacturer data
• reliable supplier information

Do not identify an unknown O-ring as NBR based only on colour.

Are all NBR 70 Shore A O-rings the same?

No.

The designation NBR 70 Shore A identifies the elastomer family and nominal hardness, but it does not define the complete rubber formulation.

Different NBR 70 ShA compounds can have different:

• chemical resistance
• temperature performance
• mechanical properties
• compression-set characteristics
• ageing behaviour
• approvals

For applications with defined technical requirements, use data for the specific compound.

NBR O-rings for industrial machinery

NBR O-rings are widely used across industrial sectors, including:

• mechanical engineering
• hydraulics
• pneumatics
• automotive systems
• agricultural machinery
• industrial automation
• maintenance and repair
• pumps
• valves
• gearboxes
• industrial equipment

Suitability of a specific O-ring must always be evaluated according to its dimensions, compound and actual service conditions.

NBR O-rings for maintenance and MRO

NBR O-rings are common replacement components in maintenance, repair and operations environments.

For MRO applications, identifying the correct replacement requires more than matching approximate diameter.

Maintenance personnel should confirm:

• ID
• CS
• material
• hardness
• operating medium
• temperature
• pressure
• original sealing conditions

Replacing an O-ring solely because another ring appears to have a similar diameter can lead to leakage, premature wear or incorrect groove compression.

Are NBR O-rings food safe?

The material designation NBR alone does not indicate food-contact approval.

Special NBR compounds are available for regulated applications, but approvals apply to the specific compound or finished product.

A standard NBR O-ring should not automatically be described as FDA compliant, food grade, EC 1935/2004 compliant or suitable for drinking water without supporting documentation.

Common mistakes when selecting NBR O-rings

A common mistake is selecting an O-ring only by its inside diameter.

The cross-section is equally important.

Other frequent mistakes include:

• ignoring the operating medium
• ignoring temperature
• confusing ID with outside diameter
• substituting another elastomer only because dimensions match
• selecting incorrect hardness
• measuring a swollen or permanently deformed used O-ring
• installing a twisted O-ring
• using an incompatible lubricant
• ignoring groove geometry
• assuming all NBR compounds have identical properties

Correct identification requires both dimensional and material information.

How to install an NBR O-ring

Before installation, clean the groove and mating surfaces.

The O-ring should not be:

• cut
• twisted
• excessively stretched
• pulled across sharp edges
• installed using sharp tools that can damage the elastomer

If an assembly lubricant is used, it must be compatible with both the NBR compound and the operating medium.

Correct installation helps reduce the risk of cutting, twisting and premature sealing failure.

How to store NBR O-rings

O-rings should be stored under conditions that minimise unnecessary elastomer ageing.

Protect them from:

• direct sunlight
• ozone sources
• excessive heat
• contamination
• permanent deformation
• incompatible chemicals

Correct storage is particularly important for industrial warehouses and maintenance departments where seals may remain in stock for extended periods before use.

Why the exact O-ring size matters

Even a small difference in cross-section can affect:

• groove filling
• sealing compression
• assembly
• friction
• extrusion risk
• sealing performance

For example, an O-ring measuring 10x2 mm is not automatically interchangeable with 10x2.5 mm.

The inside diameter is the same, but the cross-section differs by 0.5 mm.

For reliable sealing, always select the specified ID and CS.

NBR O-Ring size identification - quick guide

When identifying an NBR O-ring, follow this sequence:

O-ring -> size -> material -> hardness -> medium -> temperature -> pressure -> application

Example:

O-Ring 20x3 NBR 70 ShA

means:

• product: O-ring
• inside diameter: 20 mm
• cross-section: 3 mm
• material: NBR
• nominal hardness: 70 Shore A

This structure makes the product easier to identify both in technical documentation and online product searches.

NBR O-Rings from stock in Poland

simmering.pl supplies sealing components from stock in Poland for customers in industrial maintenance, mechanical engineering, service, repair and other technical sectors.

Warehouse and Store: Lublin, Smoluchowskiego 1 Street, Building 4.

Products are available for customers in Poland, across Europe and internationally.

We ship to customers throughout Europe and worldwide.

FAQ - NBR O-Rings

What is an NBR O-ring?

An NBR O-ring is a circular elastomeric sealing ring manufactured from Nitrile Butadiene Rubber. NBR is widely used with compatible mineral oils, greases, hydraulic fluids and in many industrial sealing applications.

What does NBR stand for?

NBR stands for Nitrile Butadiene Rubber. It is also commonly called nitrile rubber or Buna-N.

What does NBR 70 ShA mean?

NBR identifies the elastomer family, while 70 ShA means a nominal hardness of 70 on the Shore A scale.

What do ID and CS mean on an O-ring?

ID means inside diameter. CS means cross-section diameter. These are the two fundamental dimensions used to identify an O-ring.

How do I measure an NBR O-ring?

Measure the inside diameter ID and the cross-section CS. If the old O-ring is stretched, swollen or flattened, also verify the groove or original equipment documentation.

How do I calculate O-ring outside diameter?

Use the formula OD = ID + 2 x CS. For a 20x3 mm O-ring, the calculated outside diameter is 26 mm.

Are NBR O-rings resistant to oil?

NBR has good resistance to many mineral oils and greases, which is one reason it is widely used in industrial sealing. Exact compatibility depends on the compound, fluid and temperature.

Are NBR O-rings fuel resistant?

Many NBR compounds are used with fuels and hydrocarbons, but compatibility depends on the exact rubber formulation and fuel composition.

What is the temperature range of an NBR O-ring?

There is no universal temperature range for every NBR compound. Standard industrial compounds commonly operate up to approximately +100°C, but exact minimum and maximum temperatures must be verified for the specific compound.

Are NBR O-rings suitable for hydraulic systems?

Appropriately selected NBR compounds are widely used in hydraulic systems. Fluid compatibility, temperature, pressure, groove geometry and extrusion risk must be considered.

Can NBR O-rings be used in pneumatic systems?

Yes, NBR is widely used in pneumatic sealing. Correct selection depends on pressure, temperature, lubrication, movement, surface condition and groove design.

What is the difference between NBR and FKM O-rings?

NBR and FKM are different elastomer families with different chemical and temperature resistance profiles. They should be selected according to the actual medium and operating conditions.

What is the difference between NBR and EPDM O-rings?

NBR and EPDM have different chemical compatibility profiles. NBR is widely used with many mineral oils and greases, while EPDM is selected for different media and environmental conditions.

Is a black O-ring always NBR?

No. O-ring colour alone does not reliably identify the elastomer.

Are all NBR 70 Shore A O-rings identical?

No. Different NBR compounds can have the same nominal hardness while differing in chemical resistance, temperature capability, mechanical properties and approvals.

Are NBR O-rings food grade?

Not automatically. Food-contact or other regulatory approval must be confirmed for the exact compound or finished product.

Can I replace an NBR O-ring with another material of the same size?

Not automatically. Identical dimensions only establish dimensional similarity. Material compatibility with the medium, temperature and operating conditions must also be verified.

AI Overview - NBR O-Rings

NBR O-rings are circular seals manufactured from Nitrile Butadiene Rubber, also known as nitrile rubber or Buna-N. They are widely used with compatible mineral oils, greases and in hydraulic and pneumatic systems. Correct selection requires the inside diameter ID, cross-section CS, Shore A hardness, operating medium, temperature, pressure and sealing conditions.