339 Viton O-Ring 75A Durometer, 3-1/4 in ID x 3-5/8 in OD - Durable

In this review the 339 Viton O-ring is recommended for technicians, hobbyists, and maintenance teams who need a durable seal that resists heat, fuels, and many chemicals. The single biggest reason to buy is material performance: made of Viton fluorocarbon elastomer with a 75A shore durometer, it maintains seal integrity across a wide temperature range and in contact with common fuels and aromatic hydrocarbons. Reviewers who replaced worn fuel bottle seals or barrel seals found the fit and leak resistance particularly reliable.

Key Features

• Material: Viton fluorocarbon elastomer provides superior resistance to heat, fuels, and many aggressive chemicals compared with general-purpose elastomers.
• Temperature Range: Usable from -15 degrees F to 400 degrees F so it withstands demanding thermal cycles in engines and industrial systems.
• Durometer: 75A hardness balances flexibility and penetration resistance so the ring keeps shape while maintaining a tight seal under pressure.
• Cross-Section: Round profile creates a reliable seal between overlapping cylindrical surfaces, ideal for bottle necks, barrels, and fittings.
• Chemical Compatibility: Compatible with fuels, aromatic and aliphatic hydrocarbons, silicone oil, and chlorinated hydrocarbons for broad application use.
• Standards: Meets Aerospace Standard AS568A sizing conventions, which helps when replacing common specified O-rings.

Who It's For

This O-ring is best for mechanics, field technicians, and DIYers who need a dependable replacement for fuel system seals, hydraulic fittings, or vacuum and ozone-exposed components. It suits applications where heat and hydrocarbon exposure are expected, such as fuel bottles, small engines, and some firearm component seals.

Users who require compatibility with low molecular weight organic acids, strong alkalis, ammonia gas, or glycol-based brake fluids should look elsewhere, since Viton is vulnerable to those chemistries. Also avoid using it where continuous exposure to super-heated steam is anticipated.

Pros & Cons

Pros

• Excellent heat and fuel resistance keeps seals intact under high temperature and gasoline exposure.
• Customers report accurate fit and reliable leak resistance for common replacements like fuel bottle and barrel seals.
• 75A durometer offers a good balance of durability and sealing performance for pressurized joints.

Cons

• Not chemically compatible with some acids, amines, and glycol-based fluids, limiting use in certain brake or chemical systems.

Specifications

Material	Viton (fluorocarbon elastomer)
Color	Black
Cross-Section	Round
Inner Diameter (ID)	3-1/4 in
Outer Diameter (OD)	3-5/8 in
Width (cross-section)	3/16 in
Durometer	75A
Temperature Range	-15 F (-26 C) to 400 F (205 C)

Our Verdict

The 339 Viton O-ring is a practical, cost-effective choice for anyone needing a heat- and fuel-resistant seal that holds up in demanding conditions. Its 75A hardness and Viton compound make it especially suitable for fuel system replacements and high-temperature applications, delivering reliable leak resistance and long service life when used within its compatibility limits.

Frequently Asked Questions

Can this O-ring be used with gasoline and diesel?
Yes. Viton is compatible with many fuels and aromatic hydrocarbons, making this O-ring suitable for gasoline and similar fuels.

Will it work at high temperatures around 400 F?
Yes. The ring is rated up to 400 F (205 C), which covers many engine and industrial thermal conditions.

Is it suitable for brake fluid systems?
No. Viton is vulnerable to glycol-based brake fluids and should not be used where those fluids are present.