AS568-906 B90 (NBR) Buna-N Nitrile 90 Duro O-Ring (SAE -6)

Tube Size OD: 3/8", SAE Dash Size -6, Thread Size 9/16-18 UNF

Get a reliable seal for SAE straight thread boss fittings with the AS568-906 B90 Buna-N Nitrile 90 Duro O-Ring. This black 90 durometer NBR O-Ring is made for SAE -6 boss applications, helping prevent leaks in hydraulic fittings, tube connections, and equipment where oil resistance, firm sealing force, and dependable fit matter.

This O-Ring is a strong choice for maintenance teams, hydraulic repair shops, OEMs, and distributors who need a durable Boss O-Ring for petroleum-based oils, hydraulic fluids, and fuel-resistant sealing applications. The harder 90 durometer compound helps resist extrusion better than standard 70 durometer O-Rings in higher-pressure boss fitting connections.

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

Material & Performance Details

Buna-N, also called Nitrile or NBR, is one of the most widely used O-Ring materials for hydraulic and industrial sealing. This AS568-906 Boss O-Ring uses black 90 durometer NBR for added hardness, better extrusion resistance, and dependable sealing in SAE straight thread connections.

Chemical compatibility:

• Excellent resistance to:
  • Petroleum-based hydraulic oils
  • Mineral oils
  • Grease
  • Diesel fuel
  • Gasoline
  • Many aliphatic hydrocarbons
• Limited capability with:
  • Water and mild water-based fluids
  • Some alcohols
  • Some phosphate ester exposure, depending on fluid type and temperature
• Not compatible with:
  • Ozone
  • Strong acids
  • Ketones
  • Brake fluid
  • Aromatic hydrocarbons
  • Chlorinated solvents

Sizes & Measurements

• Dimensions: 3/8"ID X 5/8"OD X 5/64"CS
• Actual: 0.468"ID X 0.624"OD X 0.078"CS
• Metric: 11.89mm ID X 15.85mm OD X 1.98mm CS
• Part Number: B90906
• AS568 Dash Number: AS568-906
• SAE Dash Size: SAE -6
• Tube Size OD: 3/8"
• Thread Size: 9/16-18 UNF
• Profile Cross Reference: Boss O-Ring, SAE Straight Thread O-Ring, ORB O-Ring, SAE -6 Hydraulic Boss Seal

Applications & Use Cases

The AS568-906 B90 Buna-N O-Ring is commonly used in SAE straight thread boss fittings, hydraulic tube fittings, mobile equipment, agricultural machinery, industrial hydraulic systems, pneumatic equipment, pumps, valves, manifolds, and repair kits. It is designed to seal the boss connection on SAE -6 fittings where the O-Ring compresses between the fitting and port to prevent fluid leakage.

Key Specifications

• Material: Buna-N Nitrile, NBR
• Durometer: 90 Shore A
• Color: Black
• Size Standard: AS568-906
• Application Type: SAE Boss, ORB, straight thread tube fitting seal
• Tube Size OD: 3/8"
• SAE Dash Size: -6
• Thread Size: 9/16-18 UNF
• Temperature Range: -40° to +250°F (-40°C to +121°C)
• Certifications: Standard commercial grade unless otherwise requested
• Pressure Rating: Application dependent. Proper gland design, fitting condition, fluid type, and pressure spikes must be reviewed for critical service.

Why Buy from The O-Ring Store LLC

The O-Ring Store LLC helps customers get the right O-Ring without wasting time. We are ISO9001:2015 certified, stock common Boss O-Ring sizes in the USA, and ship in-stock items fast. Same-day shipping is available on qualifying in-stock orders, and our team can help with material selection, sizing, substitutions, and documentation when needed.

Customers benefit from competitive pricing, full lot traceability and documentation on request, custom sizes when standard sizes will not work, and experienced technical support from people who work with O-Rings every day. Our goal is simple: we make getting O-Rings easy.

Common FAQs

What fitting does the AS568-906 O-Ring fit?
The AS568-906 is commonly used for SAE -6 straight thread boss fittings with 3/8" tube OD and 9/16-18 UNF thread size.

Why use 90 durometer Buna-N instead of 70 durometer?
90 durometer Buna-N is harder and helps improve extrusion resistance in higher-pressure hydraulic boss fitting applications.

Is Buna-N good for hydraulic oil?
Yes. Buna-N Nitrile is commonly used with petroleum-based hydraulic oils, mineral oils, grease, diesel fuel, and many fuel-related sealing applications.