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Black Buna-N O-ring 4 in diameter 1/4 in cross-section pack of five

Zoro Select

Zoro Select O-Ring Buna-N 4 in 1/4 in Black PK5 70421

SKU CH-AV3H-CX9G9

Buna-N O-ring with 3.9 in inside diameter and 0.275 in width, rated for -40 to 250 °F

  • Medium-hard 70A durometer resists extrusion under pressure
  • Buna-N material handles -40 °F to 250 °F operating range
  • 4 in nominal inside diameter fits standard groove sizes
  • 1/4 in nominal cross-section provides reliable sealing contact
  • Pack of five black O-rings ready for immediate installation

Industrial O-Ring 4 in 1/4 in Buna-N

This pack contains five black Buna-N O-rings with a nominal inside diameter of 4 in and a nominal width of 1/4 in. They suit maintenance teams and engineers who need reliable static seals for hydraulic or pneumatic systems. The medium-hard 70A durometer provides a balance of compression resistance and flexibility. Buyers who need FDA-compliant materials or X-ray detectable rings should look elsewhere.

Temperature and pressure limits of Buna-N

The material operates from -40 degrees to 250 degrees F, so it handles typical industrial fluid temperatures but not extreme heat or cryogenic service. Buna-N resists petroleum oils, water and many hydraulic fluids, yet it degrades in ozone, strong acids, ketones and brake fluids. The actual inside diameter measures 3.9 in and the actual width 0.275 in, giving a precise fit for dash number 421 grooves.

Five-ring pack capacity for scheduled maintenance

A pack of five covers a standard seal replacement on a single assembly or provides spares for recurring preventive work. The actual outside diameter of 4.525 in matches common gland dimensions for this dash size. High-volume production lines or facilities running multiple identical units will need additional packs to maintain adequate stock levels.

Highlights

  • Medium-hard 70A durometer resists extrusion under pressure
  • Buna-N material handles -40 °F to 250 °F operating range
  • 4 in nominal inside diameter fits standard groove sizes
  • 1/4 in nominal cross-section provides reliable sealing contact
  • Pack of five black O-rings ready for immediate installation

Specifications

BrandZORO SELECT

Questions about this item

Which pack size or diameter should I pick for a 4-inch bore?

This pack contains five O-rings each with a nominal 4 in inside diameter and 1/4 in cross-section, matching a 4-inch bore.

What does the 70A durometer mean once the ring is installed?

A 70A durometer gives a medium-hard feel that resists extrusion at pressure while still conforming to groove surfaces.

How does the Buna-N material limit temperature and chemical exposure?

Buna-N operates from -40 to 250 °F and handles oils and fuels, but it is not FDA compliant and not X-ray detectable.

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