Mr O-Ring 427 Viton O-Ring 90A Durometer Pack of 5 - High Temp Seal

In this review the Mr O-Ring 427 Viton O-Ring is evaluated for workshop and industrial sealing tasks where heat and chemical resistance matter most. The bottom line: this pack of five black Viton o-rings is aimed at technicians, mechanics and equipment maintainers who need a compact, reliable replacement that resists fuels, oils and elevated temperatures; the single biggest reason to buy is the material performance of Viton FKM across a wide temperature and chemical range.

Key Features

• Material: Made from Viton (fluorocarbon rubber), these o-rings deliver strong resistance to fuels, mineral oils and many organic solvents useful in automotive and industrial service.
• Durometer: The 90A hardness provides a firm seal that holds shape under compression and is suitable for many static and low-dynamic sealing applications.
• Size accuracy: Nominal and actual dimensions are listed so installers can match to AS568 size standards for consistent replacement without guesswork.
• Temperature range: Rated from -26C (-15F) to 232C (450F), these rings perform in high-heat engine bays and hot-process equipment where standard elastomers would fail.
• Chemical compatibility: The compound stands up to petroleum fuels, diesel blends, methanol/ethanol mixes, silicone oils, and many industrial fluids, making it versatile for multi-system use.
• Pack convenience: Supplied as a pack of five, it is practical for small maintenance jobs or to keep spares on hand without excess inventory.

Who It's For

These o-rings are best for professional mechanics, hydraulic and pneumatic technicians, and hobbyists who need reliable seals for fuel systems, pumps, or hot-process equipment. The 90A hardness and Viton compound make them particularly suited to environments exposed to fuel, oil, ozone and sustained heat.

Those who should look elsewhere include applications that demand very soft elastomers for delicate dynamic sealing or where FDA food-grade approval is required; similarly, cryogenic uses below the stated lower limit would need a different material.

Pros & Cons

Pros

• Excellent high-temperature resistance suitable for engine and industrial applications.
• Strong chemical compatibility with petroleum, biodiesel blends and many solvents.
• Accurate nominal and actual dimensions make it easy to match AS568 sizes for direct replacements.
• Pack of five offers immediate spares for routine maintenance tasks.

Cons

• At 90A durometer the rings are relatively firm and may not be ideal for seals requiring softer, more flexible material.
• Not intended for applications needing food-grade or potable water approvals.

Specifications

Brand	Mr O-Ring
Material	Viton (FKM)
Durometer	90A
Nominal dimensions	4-3/4 in ID, 5-1/4 in OD, 1/4 in CS
Actual dimensions	4.725 in ID, 5.275 in OD, 0.275 in CS
Metric dimensions	120.02 mm ID, 134.00 mm OD, 6.99 mm CS
Temperature range	-26C (-15F) to 232C (450F)

Our Verdict

The Mr O-Ring 427 in 90A Viton offers a durable, chemically resistant replacement option for mechanics and maintenance crews who need reliable seals under heat and exposure to fuels. It is good value for those replacing AS568 sizes or stocking spares, though applications requiring softer elastomers or food-grade approval should consider alternate materials.

Frequently Asked Questions

Are these o-rings compatible with diesel and biodiesel blends?
Yes, the Viton compound is specified to perform well with diesel and blends with biodiesel and is listed for petroleum product compatibility.

Do these meet AS568 size standards?
The product notes that it meets size standards defined by AS568 and provides both nominal and actual dimensions to confirm fit.

What temperature range will these withstand?
They are rated from -26C (-15F) up to 232C (450F), suitable for many high-temperature sealing tasks.