Mr O-Ring 343 EPDM O-Ring 70A Durometer Pack of 25 - Durable Seal

In this review the Mr O-Ring 343 EPDM O-Ring is presented as a practical, no-frills pack of seals for technicians and DIYers who need reliable, weather-resistant o-rings in a common AS568 size. The bottom line: this pack of 25 o-rings offers consistent dimensions and material properties that make it an appealing choice for sealing applications exposed to ozone, steam, water and many polar solvents; the review focuses on real-world use, dimensional accuracy and material performance across temperature extremes.

Key Features

• Material: EPDM compound gives strong resistance to ozone, sunlight and weathering so seals last longer in outdoor and exposed applications.
• Durometer: 70A hardness balances flexibility and compression set resistance for general purpose sealing without being too soft or brittle.
• Size accuracy: Nominal and actual dimensions are provided so installers can match the 3-3/4' ID and 4-1/8' OD size precisely to AS568 specifications.
• Temperature range: Rated from -55C to 125C, making these o-rings suitable for cold environments and many hot fluid systems below the upper limit.
• Chemical compatibility: Performs well with alcohols, brake fluid, dilute acids and alkalis, silicone oils and water, reducing the need for multiple material types.
• Pack quantity: Sold as a pack of 25 which is convenient for maintenance spares and repetitive repair tasks.

Who It's For

The 343 EPDM o-ring pack is aimed at maintenance technicians, plumbing and hydraulic repair professionals, and hobbyists who need a reliable general-purpose seal that resists weathering and ozone. It is especially useful where a consistent bulk supply is needed for recurring maintenance jobs or inventory stocking.

Those who need resistance to petroleum-based oils, high-temperature engine oils above 125C, or specific fluorinated chemical compatibility should look at alternative elastomers. Also, applications needing ultra-precise tolerances for specialized dynamic sealing may require a different durometer or compound.

Pros & Cons

Pros

• Good environmental resistance: EPDM resists ozone, sunlight and weathering for outdoor and exposed use.
• Clear sizing: actual and nominal dimensions are listed so fitting is straightforward and repeatable.
• Versatile chemical compatibility: suitable for alcohols, brake fluid, dilute acids and many polar solvents.
• Value pack: 25 pieces provides a cost-effective supply for maintenance and repairs.

Cons

• Not suitable for petroleum-based hydraulic fluids and some oils, so compatibility must be checked before use.
• Upper temperature limit of 125C may be insufficient for some high-heat applications or continuous steam above rated max.

Specifications

Material	EPDM
Durometer	70A
Nominal dimensions	3-3/4' ID, 4-1/8' OD, 3/16' CS
Actual dimensions	3.725' ID, 4.145' OD, 0.210' CS
Metric dimensions	94.62 mm ID, 105.28 mm OD, 5.33 mm CS
Temperature range	-55C (-67F) to 125C (257F)
Pack quantity	25 pieces

Our Verdict

The Mr O-Ring 343 EPDM 70A pack is a solid, cost-effective choice for general sealing where ozone and weather resistance are priorities. For routine maintenance, plumbing and many hydraulic or steam applications within the stated temperature range it offers reliable performance and clear sizing, making it good value for those who need a dependable bulk supply.

Frequently Asked Questions

Are these o-rings suitable for outdoor use?
Yes. The EPDM material resists ozone, sunlight and weathering, making these o-rings well suited for outdoor and exposed installations.

Can I use them with engine oil or petroleum hydraulic fluid?
No. EPDM is not recommended for petroleum-based oils; use a different elastomer for those fluids to avoid swelling or degradation.

Do the actual dimensions match AS568 size standards?
Yes. The product lists nominal and actual dimensions that align with AS568 sizing for consistent fit in standard grooves.