Mr O-Ring 257 Viton O-Ring 90A Durometer, 5-7/8in ID - Pack of 25

In this review the Mr O-Ring 257 Viton O-ring is evaluated for technicians, maintenance crews and DIYers who need a durable, high-temperature sealing solution. The bottom line: this pack of 25 90A durometer Viton o-rings stands out for chemical and heat resistance, making it a reliable choice where petroleum, fuels, silicone oils or harsh environments are present. For anyone who needs multiple identical AS568-sized seals and wants consistent dimensions and long shelf life, this product delivers predictable performance without specialty handling.

Key Features

• Material: Made from Viton (FKM), the compound resists high temperature, ozone and many organic solvents to extend seal life in demanding applications.
• Hardness: The 90A durometer provides a firm seal that holds shape under pressure and repeated assembly, helping prevent extrusion and leakage in static or dynamic setups.
• Size consistency: Nominal and actual dimensions are provided so fit is reliable for parts designed to AS568 sizes, reducing trial-and-error replacements.
• Wide temperature range: Rated from -26C (-15F) to 232C (450F), these o-rings handle both low-temperature flexibility and very high operating temperatures.
• Chemical compatibility: Performs well with petroleum products, fuels, biodiesel blends, silicone oils and many acids, making it suitable for engines, pumps and hydraulic systems.
• Pack quantity: Supplied as a pack of 25, which is convenient for maintenance kits or repeated service intervals without frequent reordering.

Who It's For

This product is aimed at maintenance technicians, plumbing and hydraulic professionals, and hobbyists who need standard AS568 size Viton seals that resist heat and fuels. The pack of 25 is useful when multiple identical seals are required for production runs, periodic maintenance, or to keep a ready supply in a service vehicle.

Those who should look elsewhere include users needing a softer compound for very low-pressure static seals or applications requiring a certified food-grade or medical-grade elastomer, since this item is specified for industrial sealing performance rather than specialized certification.

Pros & Cons

Pros

• Excellent chemical and high-temperature resistance for demanding sealing tasks.
• Consistent actual dimensions (5.859in ID, 6.137in OD, 0.139in CS) reduce installation surprises.
• Pack of 25 provides good value and convenience for maintenance teams.
• Unlimited shelf life means spares can be stored without concern for aging.

Cons

• 90A durometer is relatively firm and may not seal as well in very low-pressure, highly conforming flange applications.
• Not intended where specific regulatory food or medical approvals are required.

Specifications

Material	Viton (FKM)
Durometer	90A
Nominal dimensions	5-7/8in ID, 6-1/8in OD, 1/8in CS
Actual dimensions	5.859in ID, 6.137in OD, 0.139in CS
Metric dimensions	148.82 mm ID, 155.88 mm OD, 3.53 mm CS
Temperature range	-26C (-15F) to 232C (450F)
Pack size	25 pieces

Our Verdict

The Mr O-Ring 257 Viton 90A o-ring pack is a practical choice for professionals and serious DIYers who need reliable, heat- and chemical-resistant seals in standard AS568 sizes. It offers consistent dimensions, broad compatibility with fuels and oils, and good value with 25 pieces per pack, making it a smart spare-parts investment for industrial maintenance and repair.

Frequently Asked Questions

Are these o-rings compatible with diesel and biodiesel blends?
Yes. The Viton formulation is specified to perform well with diesel and blends containing biodiesel and with fuels that include methanol or ethanol.

Will these seals handle continuous high temperatures?
They are rated to 232C (450F) and handle very high temperature air, though continuous exposure near the upper limit should be evaluated against specific operating conditions.

Do these o-rings have an expiration date?
No. The product lists an unlimited shelf life, so they can be stored as spares without a set expiration.