438 Viton O-Ring 90A, 6-1/4 in ID (Pack of 25) - High Temp Seal

In this review the Mr O-Ring 438 Viton O-Ring pack is evaluated for industrial sealing tasks where chemical and temperature resistance matter most. The bottom line: this pack of 25 delivers a consistent, high-hardness Viton seal for applications exposed to fuels, oils, ozone and elevated temperatures, so it is ideal for maintenance technicians, machine shops and fluid system installers who need reliable, repeatable replacements. The reviewer found the 90A durometer and actual dimensions provided good compression control and a long service life in demanding environments.

Key Features

• Material: Viton FKM offers superior resistance to fuels, mineral oils and many organic solvents, reducing seal failures in hydrocarbon service.
• Durometer: The 90A hardness gives a firm seal that resists extrusion and maintains shape under sustained pressure, useful for static and some dynamic sealing.
• Temperature range: Rated from -26C (-15F) to 232C (450F) so these o-rings tolerate high-temperature air and many hot fluids without rapid degradation.
• Pack size: Supplied as a pack of 25 for repeat servicing and inventory, helping shops and field techs replace multiple seals without frequent reordering.
• Size accuracy: Nominal and measured dimensions (6-1/4 in ID nominal; actual 6.225 in ID) provide predictable fit to AS568 sizing standards for easier selection.

Who It's For

The 438 Viton o-ring pack is best for industrial maintenance crews, HVAC and refrigeration technicians, and hydraulic or fuel-system repair shops that encounter petroleum products, diesel blends, silicone oils or high temperature environments. Its chemical compatibility and high temperature rating make it a good fit where longevity under stress is required.

It is less well suited for very soft-sealing applications that demand a low durometer material for delicate compression or for systems requiring FDA food-grade elastomers; in those cases a softer or food-safe elastomer should be considered.

Pros & Cons

Pros

• Excellent chemical resistance to fuels, oils, solvents and many acids, reducing replacement frequency.
• Wide temperature tolerance that performs in both very hot and moderately cold conditions.
• Consistent 90A hardness gives reliable sealing and resistance to extrusion in pressurized applications.
• Pack of 25 provides convenient stock for recurring maintenance tasks.

Cons

• 90A durometer is relatively firm and may not seal as well in low-compression or irregular surfaces compared with softer compounds.
• Not intended where food-grade or very low temperature performance below -26C is required.

Specifications

Our Verdict

The Mr O-Ring 438 Viton o-ring pack is a practical choice for professionals needing durable, high-temperature seals compatible with fuels, oils and many chemicals. With precise AS568-sized dimensions and a firm 90A durometer, it offers good value for maintenance inventories and applications where longevity and chemical resistance matter most.

Frequently Asked Questions

Are these o-rings suitable for fuel systems?
Yes; Viton FKM resists petroleum, diesel and methanol or ethanol blends, making these appropriate for many fuel-system seals.

Will the 90A hardness seal irregular surfaces?
The 90A durometer is firm and works best on properly machined or dimensional surfaces; softer compounds seal better on irregular or low-compression joints.

Do these meet a standard size?
Yes; the 438 size conforms to AS568 nominal sizing with the listed actual dimensions for reliable replacement selection.