Mr O-Ring 424 Viton O-Ring 4-3/8in ID 90A Durometer - Pack of 5

In this review the focus is on a practical, high-temperature sealing option: the Mr O-Ring 424 Viton O-Ring pack of 5. The bottom line is that this kit is aimed at technicians and hobbyists who need a durable Fluorocarbon (FKM) seal that resists fuels, oils and high heat. The single biggest reason to buy is the material and hardness combination - a 90A durometer Viton that reliably withstands temperatures up to 232C (450F) and exposure to petroleum products, making it suitable for automotive, industrial and chemical-use sealing tasks.

Key Features

• Material: Made from Viton (Fluorocarbon rubber FKM) which provides excellent resistance to fuels, hydraulic fluids and many organic solvents.
• Temperature range: Rated from -26C (-15F) to 232C (450F), giving confidence for high-temperature applications and hot-fluid exposure.
• Durometer hardness: The 90A hardness offers a firm sealing surface that stays resilient under compression and repeated cycles.
• Size accuracy: Nominal dimensions 4-3/8in ID, 4-7/8in OD with actual dimensions close to spec (4.350in ID, 4.900in OD) for reliable fitting to standardized grooves.
• Versatile compatibility: Performs well in petroleum, diesel, biodiesel blends, methanol/ethanol blends, mineral and silicone oils, and in ozone and weather-exposed environments.
• Value pack: Supplied as a pack of 5, useful for multiple repairs or spare parts inventory without needing to buy single units.

Who It's For

This Viton o-ring pack is best for maintenance mechanics, fabricators and DIYers who work with engines, pumps and fittings where exposure to fuels, oils or high temperatures is expected. Its 90A hardness and FKM compound make it a solid choice for sealing applications in automotive, industrial hydraulic or chemical systems that require resistance to aromatics and solvents.

Those who should look elsewhere include users needing very soft, low-compression-set seals (softer durometers) or applications that require food-grade or FDA-compliant elastomers, since this product is specified for chemical and temperature performance rather than food-contact certification.

Pros & Cons

Pros

• Excellent high-temperature resistance up to 232C (450F), suitable for hot-fluid seals.
• Viton FKM formula gives strong chemical resistance to fuels, oils and many solvents.
• Pack of 5 provides spare parts for repeated maintenance and reduces downtime.
• Actual dimensions closely match nominal sizes, easing replacement with AS568-sized grooves.

Cons

• 90A is a relatively firm durometer, which may not seal well in applications that require very soft, conforming o-rings.
• Not specified for food or pharmaceutical contact, so unsuitable where those certifications are required.

Specifications

Brand	Mr O-Ring
Material	Viton (Fluorocarbon rubber, FKM)
Durometer	90A
Nominal dimensions	4-3/8in ID, 4-7/8in OD, 1/4in CS
Actual dimensions	4.350in ID, 4.900in OD, 0.275in CS
Metric dimensions	110.49 mm ID, 124.47 mm OD, 6.99 mm CS
Temperature range	-26C (-15F) to 232C (450F)

Our Verdict

The Mr O-Ring 424 Viton o-ring pack is a practical, cost-effective choice for users who need a high-temperature, chemically resistant seal in automotive or industrial systems. Its 90A FKM compound and accurate sizing make it good value for maintenance kits and repair work, while the pack format keeps spares on hand for fast replacements.

Frequently Asked Questions

Can these o-rings handle fuel and oil exposure?
Yes. The Viton FKM compound is rated for petroleum products, diesel and biodiesel blends, and mineral and silicone oils.

What temperatures will these o-rings tolerate?
They are specified from -26C (-15F) up to 232C (450F), suitable for many high-temperature sealing environments.

Are these standard AS568 sizes?
Yes. The product meets size standards defined by AS568 and actual dimensions closely match the nominal sizes for reliable replacement.