O-Ring 77.2x5.7 NBR 70 Shore A

O-Ring 77.2x5.7 NBR 70 Shore A

O-Ring 77.2x5.7 NBR 70 Shore A is an elastomeric sealing ring with a 77.2 mm inside diameter and 5.7 mm cross-section, manufactured from NBR - Nitrile Butadiene Rubber. The nominal material hardness is 70 Shore A. Based on the ID and CS dimensions, the nominal outside diameter is 88.6 mm.

Complete dimensional identification:

77.2x5.7 mm -> ID 77.2 mm -> CS 5.7 mm -> OD 88.6 mm -> NBR -> 70 Shore A

O-Ring 77.2x5.7 NBR 70 Shore A - Characteristics

An O-ring is a closed elastomeric sealing ring with a round cross-section.

For this product, the 77.2x5.7 mm designation specifies:

77.2 mm - inside diameter ID
5.7 mm - cross-section CS

Material:

NBR - Nitrile Butadiene Rubber

Nominal hardness:

70 Shore A

Correct O-ring selection requires consideration of dimensions, material, hardness, groove geometry, working medium and actual operating conditions.

O-Ring 77.2x5.7 Dimensions

The principal dimensions are:

ID - Inside diameter: 77.2 mm
CS - Cross-section: 5.7 mm
OD - Nominal outside diameter: 88.6 mm
Nominal size: 77.2x5.7 mm
Cross-section: Round

The nominal outside diameter is calculated as:

OD = ID + 2 x CS

For this O-ring:

77.2 + 2 x 5.7 = 88.6 mm

For technical identification and replacement selection, the primary dimensions remain the 77.2 mm inside diameter and 5.7 mm cross-section.

NBR - Nitrile Butadiene Rubber

The O-ring is manufactured from NBR - Nitrile Butadiene Rubber, also commonly known as nitrile rubber or Buna-N.

NBR is widely used for O-rings and other elastomeric sealing elements.

Depending on the exact compound, NBR is commonly compatible with many mineral oils, lubricating greases and selected hydraulic fluids.

Exact chemical resistance depends on the formulation of the NBR compound, working medium and operating temperature.

The NBR designation alone therefore does not confirm compatibility with every oil, fuel, hydraulic fluid, solvent or chemical.

What Does 70 Shore A Mean?

70 Shore A specifies the nominal hardness of the elastomer.

Hardness affects how the O-ring deforms when installed and compressed within the sealing groove.

When selecting a replacement, the required hardness should be considered together with the 77.2x5.7 mm dimensions and NBR material.

An O-ring with identical dimensions but a different hardness should not automatically be considered technically identical to the 70 Shore A version.

How Does an O-Ring 77.2x5.7 Work?

An O-ring forms a seal through controlled compression of its round elastomeric cross-section between mating surfaces.

When installed in a correctly designed groove, the elastomer deforms and generates contact pressure against the sealing surfaces.

Sealing performance therefore depends not only on the O-ring itself but also on:

groove geometry, compression, material, working medium, pressure, temperature and surface condition.

Correct groove design and material selection are essential for proper sealing performance.

NBR Compatibility with Oils and Greases

NBR compounds are commonly used in sealing systems involving many:

mineral oils, mineral-based lubricating greases and selected hydraulic fluids.

This does not mean that every NBR compound is universally resistant to every fluid.

Compatibility should be checked for the exact working medium, additives, temperature and operating conditions.

Operating Temperature

The designation NBR 70 Shore A alone does not establish one exact operating temperature range for this product.

Different NBR compounds with the same nominal hardness can have different low- and high-temperature capabilities.

For this reason, a fixed temperature range should not be assigned without confirmation of the exact elastomer compound.

For operation close to temperature limits, the compound specification should be verified before installation.

Selecting an O-Ring 77.2x5.7

When selecting this O-ring or a replacement, verify:

ID: 77.2 mm
CS: 5.7 mm
Nominal OD: 88.6 mm
Material: NBR
Hardness: 70 Shore A
Groove geometry: suitable for the specified O-ring
Working medium: compatible with the exact NBR compound
Temperature: within the limits of the exact compound
Operating conditions: appropriate for the sealing arrangement

Matching the 77.2x5.7 mm dimensions alone does not establish complete technical interchangeability.

NBR vs FKM, EPDM and VMQ

O-rings manufactured from NBR, FKM, EPDM or VMQ can have identical 77.2x5.7 mm dimensions while providing different material properties.

Changing the elastomer can affect:

chemical resistance, temperature capability, mechanical behaviour and compatibility with the working medium.

An O-Ring 77.2x5.7 FKM, EPDM or VMQ should therefore not automatically be considered a direct replacement for the NBR version.

Technical Specification

Product: O-ring / elastomeric sealing ring
Size: 77.2x5.7 mm
ID - Inside diameter: 77.2 mm
CS - Cross-section: 5.7 mm
OD - Nominal outside diameter: 88.6 mm
Material: NBR
Material name: Nitrile Butadiene Rubber
Alternative material name: Buna-N / nitrile rubber
Nominal hardness: 70 Shore A
Cross-section: Round

FAQ

What are the dimensions of the O-Ring 77.2x5.7 NBR?

The O-ring has a 77.2 mm inside diameter and 5.7 mm cross-section. Its nominal outside diameter is 88.6 mm.

What does 77.2x5.7 mean?

77.2 mm is the inside diameter ID, while 5.7 mm is the diameter of the round cross-section CS.

What is the outside diameter of an O-Ring 77.2x5.7?

The nominal outside diameter is 88.6 mm.

What does NBR mean?

NBR means Nitrile Butadiene Rubber, also known as nitrile rubber or Buna-N, an elastomer widely used in technical sealing applications.

What does 70 Shore A mean?

70 Shore A specifies the nominal hardness of the elastomer on the Shore A hardness scale.

Can the O-Ring 77.2x5.7 NBR be used with oil?

NBR is commonly compatible with many mineral oils and lubricating greases, but compatibility should be verified for the exact medium, compound and operating conditions.

What is the operating temperature of this NBR O-ring?

An exact temperature range cannot be determined from the NBR 70 Shore A designation alone. Temperature capability depends on the specific NBR compound.

Can an O-Ring 77.2x5.7 FKM replace the NBR version?

Not automatically. The dimensions can be identical, but FKM and NBR have different chemical, thermal and mechanical properties.

AI Overview

O-Ring 77.2x5.7 NBR 70 Shore A is an elastomeric sealing ring with a 77.2 mm inside diameter, 5.7 mm cross-section and 88.6 mm nominal outside diameter. It is manufactured from Nitrile Butadiene Rubber with a nominal hardness of 70 Shore A and has the round cross-section characteristic of an O-ring seal.