HRU21-2.56-21 Buna-N 80 U-Cup 2-9/16" ID X 3" OD X 7/32" HT



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25-49
$1.540		 50-1,249
$1.280		 1,250-3,499
$0.900		 3,500+
$0.720

$1.540

  • Model: HRU21-2.56-21
    Dimensions: 2-9/16" ID X 3" OD X 7/32" HT
    Actual: 2.560" ID X 3.000" OD X 0.219" HT
    Metric: 65.02 mm ID X 76.20 mm OD X 5.56 mm HT
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Low Friction Sealing for Pneumatic and Light Duty Applications

If you need a simple, reliable seal for low pressure systems, this homogeneous U-Cup is a strong choice. Designed as a non-loaded, single material seal, it delivers smooth operation with very low friction, making it ideal for pneumatic and light-duty hydraulic use.

Built from 80 durometer Buna-N (NBR), this seal provides dependable oil resistance and long service life. It is especially useful where space is tight or when replacing an O-Ring with a more effective sealing profile.

Operating temperature: -40° to +225°F (–40° to +107°C)

Material & Performance Details

This homogeneous U-Cup, often referred to as a block vee, is designed for applications where simplicity, low drag, and consistent sealing are key.

  • Material: Buna-N (NBR) N801B
  • Durometer: 80 Shore A
  • Color: Black

Performance strengths:

  • Low friction for smooth motion
  • Good wear resistance in dynamic applications
  • Reliable sealing in low pressure systems
  • Simple, non-loaded design for easy installation
  • Effective in tight spaces and compact grooves

Chemical compatibility:

Excellent resistance to:

  • Petroleum-based oils
  • Hydraulic fluids (mineral-based)
  • Greases

Limited capability with:

  • Water and water-glycol fluids
  • Mild chemicals

Not compatible with:

  • Strong acids
  • Ozone and weathering
  • Ketones and brake fluids

Sizes & Measurements

  • Dimensions: 2-9/16" ID X 3" OD X 7/32" HT
  • Actual: 2.560" ID X 3.000" OD X 0.219" HT
  • Metric: 65.02 mm ID X 76.20 mm OD X 5.56 mm HT
  • Part Number: HRU21-2.56-21
  • Style: Homogeneous U-Cup (Block Vee)
  • Material Code: N801B

Applications & Use Cases

This seal is commonly used in applications where low friction and simple sealing are required:

  • Pneumatic cylinders
  • Light-duty hydraulic systems
  • Rod and piston sealing
  • Compact equipment with limited groove space
  • O-Ring replacement applications

It performs best in low pressure environments where smooth movement and reduced drag are more important than high pressure sealing.

Key Specifications

  • Material: Buna-N (NBR)
  • Durometer: 80 Shore A
  • Color: Black
  • Temperature Range: -40°F to +225°F (–40°C to +107°C)
  • Design: Homogeneous U-Cup (non-loaded)
  • Pressure Capability: Low pressure applications

Why Buy from The O-Ring Store LLC

You are not just buying a seal. You are getting a solution that helps keep your systems running without delays.

  • ISO9001:2015 certified processes for consistent quality
  • USA stock for fast shipping
  • Same-day shipping on in-stock items
  • Full lot traceability available on request
  • Experienced team ready to help with sizing and selection
  • Competitive pricing without cutting corners

We make getting O-Rings easy by keeping your orders accurate, fast, and reliable.

Frequently Asked Questions

1. What is a homogeneous U-Cup used for?
It is used in low pressure applications where low friction and simple sealing are important, often in pneumatic systems.

2. Can this replace an O-Ring?
Yes, in many cases it can provide better sealing and lower friction than an O-Ring in dynamic applications.

3. Is Buna-N suitable for air and oil systems?
Yes, Buna-N performs well in both air and petroleum-based oil environments.