Mr O-Ring 348 Viton O-Ring 4-3/8 in ID Pack of 25 - High Temp Seal

In this review the Mr O-Ring 348 Viton o-ring pack is evaluated for technicians, maintenance pros and DIYers who need a reliable sealing solution for high temperature or fuel-exposed systems. The bottom line: this 90A durometer Viton o-ring stands out for its temperature range and chemical resistance, making it a practical choice where mineral oils, fuels, silicone oils, ozone or weather exposure are expected. The pack of 25 covers repeated service needs and the o-ring sizes adhere to AS568 standards, so replacements and inventory management are straightforward for workshops and field crews.

Key Features

• Material: Made from Viton (FKM), the rubber offers strong resistance to high temperature and many chemicals encountered in industrial service.
• Durometer: The 90A hardness gives a firm sealing surface that resists extrusion while still providing reliable compression sealing.
• Dimensions: Nominal 4-3/8 in ID and 4-3/4 in OD with actual 4.350 in ID and 4.770 in OD, which helps ensure an accurate fit in AS568 applications.
• Temperature range: Rated from -26C (-15F) to 232C (450F), suitable for very high temperature air and hot fluid environments.
• Chemical compatibility: Performs well with petroleum products, fuels, biodiesel blends, methanol or ethanol blends, mineral and silicone oils and many solvents.
• Pack size: Supplied in a pack of 25, which is convenient for repeated maintenance cycles or stocking in a service shop.

Who It's For

The Mr O-Ring 348 Viton is best for maintenance technicians, mechanics and HVAC or hydraulic specialists who require durable seals that tolerate high temperatures and exposure to fuels and oils. It is also useful for manufacturers and fabricators who maintain equipment with AS568 size requirements and prefer bulk packs for inventory.

Those who need extremely soft, low-durometer seals for delicate pneumatic systems or who require elastomers designed for prolonged exposure to strong caustics should look elsewhere; Viton is optimized for heat and hydrocarbon resistance rather than the soft sealing feel of low-hardness elastomers.

Pros & Cons

Pros

• Excellent high temperature stability and broad chemical resistance for fuel- and oil-exposed systems.
• 90A hardness resists extrusion and provides a reliable compression seal in demanding applications.
• Pack of 25 makes it easy to service multiple units and keep spare inventory on hand.
• Actual and metric dimensions are provided, aiding correct selection and installation.

Cons

• At 90A durometer the o-ring is relatively firm, which may not be ideal where a softer compressible seal is required.
• Viton is less suited for prolonged exposure to certain strong caustic solutions, so chemical compatibility should be confirmed for specific fluids.

Specifications

Material	Viton (FKM)
Durometer	90A
Nominal dimensions	4-3/8 in ID, 4-3/4 in OD, 3/16 in CS
Actual dimensions	4.350 in ID, 4.770 in OD, 0.210 in CS
Metric dimensions	110.49 mm ID, 121.15 mm OD, 5.33 mm CS
Temperature range	-26C (-15F) to 232C (450F)
Pack size	25 pieces

Our Verdict

The Mr O-Ring 348 Viton 90A pack is a solid, cost-effective choice for professionals who need dependable seals that resist heat, fuels and oils. Its AS568 sizing, clear actual dimensions and bulk pack format deliver good value for workshops and field service; choose a softer elastomer only if your application specifically requires lower durometer material.

Frequently Asked Questions

Are these o-rings compatible with diesel and biodiesel?
Yes, the Viton material is formulated to perform well with diesel and blends containing biodiesel as listed in the product details.

Do the dimensions follow a standard size?
Yes, these o-rings meet AS568 size standards and the listing includes both nominal and actual dimensions to confirm fit.

What environments are unsuitable for Viton?
Viton is not ideal for prolonged exposure to strong caustic solutions or environments demanding very soft, low-durometer sealing surfaces.