368 Viton O-Ring 75A Durometer, 7-3/4 in ID - Durable Chemical Seal

In this review the 368 Viton O-ring is evaluated for routine industrial sealing and replacement use; the bottom line is that it is a reliable, heat- and fuel-resistant replacement that suits applications needing chemical compatibility and size accuracy. The reviewer found the pack of 10 useful for repeat maintenance tasks, particularly where a round-section seal and a 75A hardness are required. Its ability to withstand a wide temperature range and resist many fuels and solvents makes it a practical choice for technicians and hobbyists replacing MSA fuel bottle seals, firearm barrel seals, or Silencerco switchback components.

Key Features

• Material: Made of Viton fluorocarbon elastomer, it provides strong resistance to heat, fuels, and many chemicals commonly encountered in industrial and automotive settings.
• Temperature range: Rated for -15 degrees F to 400 degrees F, it remains flexible in cold service and stable under high heat exposure.
• Durometer: The 75A hardness balances compression resistance and conformability so the ring holds a seal without being excessively stiff.
• Cross-section: Round cross-section design provides consistent sealing between overlapping cylindrical surfaces for reliable leak control.
• Compatibility: Suitable for non-flammable hydraulic fuels, silicone oils, chlorinated and aromatic hydrocarbons, and high vacuum and ozone-exposed environments.
• Pack size: Ten identical O-rings in the specified size make it economical for maintenance kits and repeated replacements.

Who It's For

This O-ring is aimed at maintenance technicians, plumbers, small engine mechanics, firearm and suppressor owners, and hobbyists who need precise, heat-resistant seals in plumbing, fuel systems, or hydraulic components. Its compatibility with a wide range of hydrocarbons and resistance to ozone makes it useful in outdoor and high-temperature environments.

Those working with aggressive low molecular organic acids, ammonia gas, alkalis, amines, glycol-based brake fluids, or super-heated steam should look elsewhere or verify chemical compatibility first, since Viton is vulnerable to those substances and may degrade under prolonged exposure.

Pros & Cons

Pros

• Excellent resistance to fuels, aromatic and aliphatic hydrocarbons, and many solvents, so it performs well in fuel-system and chemical-exposed applications.
• Wide usable temperature range from -15 degrees F to 400 degrees F, offering versatility across environments.
• Appropriate 75A durometer offers a good balance of durability and sealing conformity for cylinder overlaps.
• Pack of 10 offers good value for repeat replacements and routine maintenance.

Cons

• Not compatible with certain substances such as ammonia, strong alkalis, some brake fluids, and super-heated steam, which limits use in chemically aggressive systems.

Specifications

Material	Viton (fluorocarbon elastomer)
Color	Black
Inner Diameter (ID)	7-3/4 in
Outer Diameter (OD)	8-1/8 in
Width	3/16 in
Durometer	75A
Temperature Range	-15 degrees F to 400 degrees F

Our Verdict

The 368 Viton O-ring is a practical, value-minded choice for anyone needing a heat- and fuel-resistant round-section seal in the specified size. For common fuel, hydraulic, and outdoor sealing tasks it offers good durability and leak resistance, and the pack of 10 makes it economical for maintenance. Avoid it only where exposure to incompatible chemicals or super-heated steam is expected.

Frequently Asked Questions

Is this O-ring suitable for fuel-system use?
Yes; Viton is compatible with many fuels, aromatic and aliphatic hydrocarbons, and non-flammable hydraulic fluids, making it suitable for many fuel-system seals.

Will it handle high temperatures?
Yes; the O-ring is rated to 400 degrees F, so it performs well in high-temperature applications within that limit.

Are there chemicals to avoid?
Avoid prolonged exposure to low molecular organic acids, ammonia, alkalis, amines, glycol-based brake fluids, and super-heated steam, as Viton can be vulnerable to those substances.