AS568-109 SN90 (NBR) Buna-N 90 Duro Square O-Ring

Buna-N 90 Duro square O-Rings are black NBR rubber seals designed for oil resistance, firm sealing pressure, and dependable performance in hydraulic, pneumatic, pump, valve, and general industrial applications.

A Buna-N 90 Duro Square O-Ring is built for customers who need a firm, oil-resistant seal with more surface contact than a standard round O-Ring. The square profile can help improve sealing contact in properly designed grooves, making it a strong choice for static sealing and industrial repair work.

Made from black Buna-N Nitrile rubber, 90 Shore A durometer, this seal offers good resistance to petroleum oils, grease, fuel, and hydraulic fluids. The harder 90 Duro compound helps resist extrusion, deformation, and compression damage in demanding applications.

Operating Temperature

Operating temperature: -40° to +250°F (–40° to +121°C)

Material & Performance Details

Buna-N, also known as NBR or Nitrile, is one of the most common sealing materials used in industrial, hydraulic, and mechanical equipment. It is valued for its oil resistance, abrasion resistance, and reliable sealing performance in petroleum-based fluid systems.

The 90 Duro hardness makes this square O-Ring firmer than standard 90 Duro Buna-N seals. This helps when the application needs added resistance to extrusion, movement, or higher sealing stress.

Excellent resistance to:

• Petroleum-based oils
• Hydraulic fluids
• Diesel fuel
• Gasoline
• Grease
• Mineral oil
• Air
• Water

Limited capability with:

• Some biofuels
• Mild chemicals
• Short-term outdoor exposure
• Low aromatic fuel blends

Not compatible with:

• Brake fluid
• Ketones
• Ozone-heavy environments
• Strong acids
• Chlorinated solvents
• Phosphate ester hydraulic fluids

Applications & Use Cases

Buna-N 90 Duro square O-Rings are commonly used in hydraulic systems, pneumatic equipment, pumps, valves, fittings, industrial machinery, repair kits, and maintenance applications. They are a practical choice when a customer needs oil resistance, a firmer seal, and improved gland contact in a square-profile sealing design.

Key Specifications

• Material: Buna-N, NBR, Nitrile
• Durometer: 90 Shore A
• Color: Black
• Profile: Square O-Ring
• Temperature Range: -40° to +250°F (–40° to +121°C)
• Certifications: Standard commercial grade unless otherwise listed
• Pressure Rating: Application dependent, based on gland design, clearance gap, fluid, and pressure

Why Buy from The O-Ring Store LLC

At The O-Ring Store LLC, we make getting O-Rings easy. Customers benefit from ISO9001:2015 certified quality processes, stocked USA inventory, same-day shipping on in-stock items, and clear product information that helps reduce ordering mistakes.

We offer custom sizes, full lot traceability and documentation on request, and experienced technical support when you need help choosing the right seal. You get competitive pricing without giving up service, accuracy, or accountability. That matters when downtime costs more than the O-Ring.

FAQs

What is a Buna-N 90 Duro square O-Ring used for?
It is used for sealing applications that need oil resistance, a firmer compound, and more sealing surface contact than a standard round O-Ring.

Is Buna-N 90 Duro good for hydraulic oil?
Yes. Buna-N 90 Duro is commonly used with petroleum-based hydraulic oils. The harder material helps improve extrusion resistance compared to softer Buna-N compounds.

Can a square O-Ring replace a round O-Ring?
Only when the groove design allows it. Square O-Rings and round O-Rings compress differently, so the gland design should be checked before substituting.