249 O-Ring Buna-N 90A 4-7/8in ID 5-1/8in OD Pack of 50 - Durable Seal

In this review the 249 O-Ring in black Buna-nitrile is evaluated for workshop and hydraulic use; the bottom line is that it is a simple, heavy-duty sealing solution for anyone needing a firm, oil-compatible O-ring in common aerospace sizes. The reviewer found the set of 50 particularly useful for technicians, home mechanics and small shops who want consistent, standardized parts on hand, and the single biggest reason to buy is the material and hardness combination - Buna-N 90A - which delivers resistance to petroleum fluids while remaining dimensionally stable across a wide temperature range.

Key Features

• Material: Buna-nitrile construction provides compatibility with petroleum, HFC fluids, vegetable oil and many aliphatic hydrocarbons, reducing seal failures in common systems.
• Hardness: The 90A durometer makes these O-rings stiff and abrasion resistant, which helps maintain seals under compression and repeated coupling cycles.
• Standard Size: Molded to AS568A aerospace dimensions for reliable fit in any component sized to that standard, simplifying replacements.
• Temperature Range: Rated from -40 degrees F to 212 degrees F, this O-ring covers most indoor and engine bay applications without rapid degradation.
• Cross-section: A round profile forms a dependable seal between overlapping cylindrical surfaces, effective in hose couplers and hydraulic fittings.
• Value Pack: Sold in a pack of 50 so users can keep spares on hand and avoid downtime from waiting for replacements.

Who It's For

This product suits maintenance technicians, plumbers working with petroleum-based fluids, small engine mechanics, and hobbyists who need a bulk supply of AS568A-compliant O-rings. Its durability and resistance to common oils make it a practical choice for items like garden hose quick disconnects, hydraulic couplers and kayak fittings.

Those who need extreme flexibility at very low temperatures, specialty chemical resistance to ethers or esters, or exposure to sunlight and ozone should look elsewhere, as Buna-nitrile is vulnerable to solvents like acetone and to weathering over long outdoor exposure.

Pros & Cons

Pros

• Good compatibility with petroleum and many hydrocarbon fluids, preventing common leaks.
• High durometer gives strong abrasion and tear resistance for repeated service cycles.
• Pack of 50 offers clear value for frequent replacements or workshops.
• Made to AS568A size standard for predictable fit in compatible hardware.

Cons

• At 90A the O-rings are fairly stiff and feel hard like plastic, which can make installation into tight grooves more difficult.
• Not suitable for use with acetone, ethers, esters or prolonged outdoor ozone and UV exposure.

Specifications

Material	Buna-nitrile (Buna-N)
Durometer	90A
Inner Diameter	4-7/8 in
Outer Diameter	5-1/8 in
Cross-section Width	1/8 in
Color	Black
Temperature Range	-40 degrees F to 212 degrees F

Our Verdict

The 249 Buna-N 90A O-ring pack is a practical, cost-effective choice for anyone maintaining hydraulic couplers, garden hose fittings or general machinery that uses petroleum-based fluids; its adherence to AS568A sizing and robust hardness make it a reliable spare-part solution. Buyers who need softer seals or resistance to solvents and ozone should consider other elastomers, but for standard sealing tasks this pack represents good value.

Frequently Asked Questions

Are these O-rings compatible with petroleum oils?
Yes, Buna-nitrile is compatible with petroleum and many aliphatic hydrocarbons, making these suitable for oil-based systems.

Will the 90A hardness make installation difficult?
The 90A rating is quite stiff, so installation into tight grooves may require care or lubrication but provides better abrasion and tear resistance once installed.

Do these O-rings resist extreme cold and heat?
They are rated from -40 degrees F to 212 degrees F, covering most indoor, engine bay and equipment applications but not extreme cryogenic or very high-temperature uses.