Mr O-Ring 343 Viton O-Ring 90A Durometer - Pack of 5

In this review the Mr O-Ring 343 Viton O-Ring is examined for technicians and DIYers who need a durable seal that handles fuels, oils and high heat. The bottom line: this 90A durometer Viton o-ring delivers predictable chemical and temperature resistance for demanding sealing tasks, and the pack of 5 makes it easy to keep spares on hand. Performance in petroleum, biodiesel blends, silicone oils and high-temperature applications is the single biggest reason a mechanic or maintenance pro will reach for this size.

Key Features

• Material: Viton FKM construction gives excellent resistance to fuels, oils and many organic solvents, reducing seal failures in contact with aggressive fluids.
• Temperature range: Rated from -26C (-15F) to 232C (450F), it maintains sealing integrity across high-heat engine or industrial environments.
• Hardness: The 90A durometer provides a firm cross-section that resists extrusion while still compressing to form a reliable seal.
• Size accuracy: Nominal and actual dimensions are provided so fit can be verified before installation, helping avoid returns or reorders.
• Versatile compatibility: Performs well in petroleum, methanol or ethanol blends, biodiesel blends, mineral and silicone oils, ozone and weather exposure for broad application use.
• Quantity: Sold as a pack of 5, offering immediate spares for repairs or routine maintenance.

Who It's For

This o-ring is best for automotive technicians, small engine repair shops and industrial maintenance teams that need a compact, high-temperature resistant seal compatible with fuels, hydraulic fluids and many solvents. The firmness and Viton chemistry make it a solid choice where elevated temperature and chemical exposure are common.

Those who need very soft seals for delicate instrumentation or who require food-grade elastomers should look elsewhere; Viton is not intended for food contact applications. Also, if a metric-native inventory or different durometer is required, pick a product sized or rated specifically for that use.

Pros & Cons

Pros

• Excellent chemical resistance to fuels, oils and many solvents, which reduces premature deterioration.
• High temperature capability up to 232C (450F) allows use near hot engine or process components.
• 90A hardness resists extrusion and provides durable sealing under pressure.
• Pack of 5 gives spare parts on hand for repairs or routine replacements.

Cons

• Higher durometer makes it less suitable for applications needing a very soft, low-pressure seal.
• Not intended for food or beverage contact, limiting some sanitary uses.

Specifications

Brand	Mr O-Ring
Material	Viton (FKM)
Durometer	90A
Nominal size	3-3/4 in ID, 4-1/8 in OD, 3/16 in CS
Actual dimensions	3.725 in ID, 4.145 in OD, 0.210 in CS
Metric dimensions	94.62 mm ID, 105.28 mm OD, 5.33 mm CS
Temperature range	-26C (-15F) to 232C (450F)

Our Verdict

The Mr O-Ring 343 Viton 90A is a practical, cost-effective choice for mechanics and maintenance pros who need a heat- and chemical-resistant seal in a reliable AS568 size. Its durable 90A hardness and wide compatibility make it good value for industrial and automotive sealing tasks, and the five-pack format keeps spares on-hand for quick repairs.

Frequently Asked Questions

Is this o-ring compatible with diesel and biodiesel blends?
Yes. The Viton formulation performs well with diesel and common biodiesel blends without rapid deterioration.

Can it be used at high vacuum or ozone-exposed locations?
Yes. Viton offers good performance in high vacuum and resists ozone and weathering better than many elastomers.

Does the pack include five identical o-rings?
Yes. This listing supplies a pack of five identical Mr O-Ring 343 Viton o-rings for spare parts or multiple installations.