345 Viton O-Ring 75A Durometer 4in ID 4-3/8in OD - Reliable Chemical

In this review the 345 Viton O-Ring is presented as a practical replacement seal for industrial, hydraulic and fuel-handling applications; its chief selling point is chemical and heat resistance thanks to the Viton compound. For technicians, hobbyists and maintenance staff who need an O-ring that holds up to high temperatures and many fuels, this pack of 10 provides consistency of size and material. The review focuses on fit, material performance and typical use cases based on customer feedback and the product specification.

Key Features

• Material: Made of Viton fluorocarbon elastomer to resist fuels, oils and many chemicals for longer service life.
• Temperature range: Rated from -15 degrees F to 400 degrees F so it performs across cold starts and high-heat operating environments.
• Durometer: 75A hardness provides good resistance to penetration and reliable compression set for sealing cylindrical surfaces.
• Form factor: Round cross-section designed to seal between overlapping cylindrical parts without custom machining.
• Standards: Manufactured to meet Aerospace Standard AS568A sizing conventions for predictable interchangeability.

Who It's For

This O-ring pack is best for maintenance technicians, machinists and end users who need a small stock of correctly sized seals for fuel bottles, firearm components, vacuum fittings or hydraulic assemblies. The chemical compatibility and wide temperature allowance make it suitable for non-flammable hydraulic fuels, silicone oils, aromatic and aliphatic hydrocarbons, and many workshop environments.

Those who should look elsewhere include users needing resistance to low molecular organic acids, ammonia gas, alkalis, amines, glycol-based brake fluids or continuous exposure to super-heated steam, since Viton can be vulnerable to those agents. Also, if a softer shore hardness than 75A is required for delicate low-pressure seals, pick a different durometer.

Pros & Cons

Pros

• Excellent heat and fuel resistance, making it reliable in high-temperature or fuel-exposed applications.
• Consistent sizing and fit that customers report working well for MSA fuel bottle seals and Remington barrel seals.
• Good value in a pack of 10 for replacements and preventive maintenance spares.

Cons

• Not compatible with certain chemicals such as ammonia, strong alkalis, amines or glycol-based brake fluids, limiting use in some specialty fluids.
• 75A hardness may be too firm for some low-pressure or delicate sealing needs where a softer compound is preferred.

Specifications

Material	Viton (fluorocarbon elastomer)
Color	Black
Inner diameter (ID)	4 in
Outer diameter (OD)	4-3/8 in
Cross-section / Width	3/16 in
Durometer	75A
Temperature range	-15 degrees F to 400 degrees F

Our Verdict

The 345 Viton O-Ring pack is a solid, no-nonsense choice for anyone who needs chemical and heat-resistant seals in standard AS568A sizes. It is particularly good value for spares and repairs where fuel and high temperature exposure are expected, though users with compatibility concerns for specific chemicals or who need a softer compound should choose an alternative.

Frequently Asked Questions

Are these O-rings compatible with gasoline and diesel?
Yes; Viton is compatible with many fuels and aromatic and aliphatic hydrocarbons, making these O-rings suitable for typical gasoline and diesel exposure.

Will the 75A hardness work for firearm seals and switches?
Customers report good fit and functionality for Remington 1100 barrel seals and Silencerco switchback applications, but performance depends on the specific seal design and compression required.

Can I use these in brake fluid systems?
No; Viton is vulnerable to glycol-based brake fluids, so do not use these O-rings where constant contact with such fluids is expected.