Mr O-Ring 343 Viton O-Ring 90A Durometer - Pack of 25

In this review the Mr O-Ring 343 Viton O-Ring is evaluated for technicians and hobbyists who need a high-temperature, chemical-resistant sealing solution. The bottom line: this pack of 25 delivers consistent, AS568-sized performance with a 90A durometer that resists fuels, oils and heat, making it a practical choice for repair shops, HVAC and fluid-handling systems where compatibility and longevity matter. The review highlights fit, material performance and typical use cases based on the product's specifications.

Key Features

• Material: Viton FKM construction provides strong resistance to high temperature, ozone and many organic solvents, helping seals last longer in demanding environments.
• Hardness: The 90A durometer offers a firm cross-section that maintains sealing pressure while resisting extrusion under moderate compression.
• Size accuracy: Nominal and actual dimensions are provided so installers can verify fit; precise measurements reduce guesswork during replacement.
• Chemical compatibility: Performs well in petroleum products, diesel blends, biodiesel, methanol/ethanol blends, mineral oils and silicone lubricants, expanding its use across systems.
• Temperature range: Rated -26C to 232C (-15F to 450F), making it suitable for high-temperature air and many heated fluid applications.
• Pack quantity: Supplied in a pack of 25 for maintenance jobs or multiple repairs, helping shops keep common sizes on hand.

Who It's For

The Mr O-Ring 343 is aimed at mechanics, maintenance technicians and serious DIYers who need a reliable Viton seal for fuel systems, hydraulic connections or high-temperature sealing points. Its broad chemical resistance and high temperature rating make it especially useful in applications exposed to fuels, oils and solvents where standard nitrile O-rings would fail.

Those working exclusively with low-temperature, food-grade, or very soft-sealing requirements may want to look at alternate elastomers or softer durometers; the 90A hardness here is relatively firm and better suited to pressurized or high-temperature settings rather than delicate low-load static seals.

Pros & Cons

Pros

• Excellent chemical and temperature resistance from Viton FKM means fewer replacements in harsh environments.
• Pack of 25 offers good value for workshops and routine maintenance tasks.
• Actual and metric dimensions provided make sizing straightforward and reduce installation errors.
• 90A durometer keeps shape under pressure, improving seal reliability in many dynamic systems.

Cons

• Relatively firm 90A hardness may be too stiff for delicate or very low-compression sealing needs.
• Viton is more expensive than common elastomers, so cost-conscious users for simple non-chemical applications might prefer a cheaper material.

Specifications

Material	Viton (FKM)
Durometer	90A
Nominal dimensions	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 to 232C (-15F to 450F)
Pack quantity	25 o-rings

Our Verdict

The Mr O-Ring 343 Viton 90A in a pack of 25 is a solid choice for professionals and serious DIYers who need a high-temperature, fuel-resistant seal that matches AS568 sizing. It represents good value where chemical compatibility and durability matter, though users needing softer seals should consider different durometers.

Frequently Asked Questions

Is this o-ring compatible with fuel and oil?
Yes. The Viton FKM compound is rated for petroleum products, diesel and many fuel blends, making it suitable for fuel and oil sealing applications.

What temperature range can it handle?
The o-ring is rated from -26C to 232C (-15F to 450F), suitable for most high-temperature air and heated fluid uses.

Are the sizes exact for replacements?
Actual dimensions are listed (3.725 in ID, 4.145 in OD, 0.210 in CS) so you can confirm fit for AS568-based applications.