357 O-Ring Buna-N 90A 5-1/2in ID 25-Pack - Durable Seal

In this review the 357 O-Ring in black Buna-N is recommended for users who need a hard, dependable seal for petroleum and similar fluids; the single biggest reason to buy is its combination of a firm 90A durometer and Aerospace AS568A sizing that delivers consistent sealing performance in demanding hydraulic and plumbing fittings. The pack of 25 makes it a practical choice for maintenance tasks, and the material's resistance to abrasion, tear and compression set means these rings hold up where a softer elastomer might fail.

Key Features

• Material: Buna-nitrile formulation offers compatibility with petroleum, HFCs, vegetable oil and many aliphatic hydrocarbons for broad application use.
• Hardness: 90A durometer gives a stiff, reliable seal for couplers and fittings that require low deformation under pressure.
• Size standard: Manufactured to AS568A dimensions so the 5-1/2in ID and 5-7/8in OD fit standard grooves and cylinders with predictable results.
• Temperature range: Rated from -40 degrees F to 212 degrees F, suitable for most outdoor and workshop environments.
• Durability: Good tensile, abrasion and tear resistance helps these O-rings resist wear in repeated-use applications.

Who It's For

These O-rings are aimed at industrial and home mechanics, plumbing and hydraulic technicians, and anyone replacing seals on garden quick disconnects, kayak fittings, or couplers where a firmer seal is preferred. The pack size suits shops and hobbyists who do routine maintenance and need multiple identical rings on hand.

Those who need a softer, highly flexible seal for delicate instruments or long-term outdoor exposure to ozone and sunlight should look elsewhere, since Buna-N is vulnerable to ozone, esters and strong ketones and these rings are relatively stiff compared with lower durometer compounds.

Pros & Cons

Pros

• High durometer and good abrasion resistance provide a durable seal for hydraulic couplers and similar fittings.
• AS568A sizing means reliable interchangeability with standard O-ring grooves and components.
• Wide chemical compatibility with petroleum, HFCs, vegetable oil and many aliphatic hydrocarbons.

Cons

• Firm 90A hardness can feel stiff and like hard plastic for some users, limiting use where a softer gasket is required.

Specifications

Material	Buna-nitrile (Buna-N)
Durometer	90A
Inner diameter	5-1/2 in
Outer diameter	5-7/8 in
Cross-section width	3/16 in
Temperature range	-40 degrees F to 212 degrees F
Pack quantity	25

Our Verdict

The 357 Buna-N 90A O-ring is a practical, value-minded choice for anyone needing a tough, standardized seal in hydraulic, plumbing or outdoor gear repairs; its hard durometer and AS568A sizing make replacement predictable and long-lasting, though buyers needing softer or ozone-resistant material should consider alternatives.

Frequently Asked Questions

Will these O-rings resist petroleum-based fluids?
Yes, Buna-nitrile is compatible with petroleum and many aliphatic hydrocarbons, making these suitable for oil and fuel-related seals.

Are these rings suitable for low-temperature use?
Yes, they are rated down to -40 degrees F, so they remain functional in most cold-weather environments.

Do they meet standard O-ring sizing?
Yes, they conform to AS568A aerospace sizing, so the 5-1/2in ID and 5-7/8in OD match standard grooves for the 357 size.