Mr O-Ring 345 EPDM O-Ring 4in ID 70A Durometer - Pack of 25

In this review the focus is on a simple, dependable sealing solution for workshops and maintenance departments: the Mr O-Ring 345 EPDM O-Ring, supplied in a pack of 25. The bottom line is straightforward: this kit is for anyone who needs a consistent, weather-resistant EPDM seal in the common 4 in nominal size with reliable temperature tolerance. The reviewer found the rings meet nominal AS568 sizing, offer broad chemical compatibility, and provide good flexibility at low temperature, making them a practical spare-parts purchase rather than a specialty elastomer for fuel or oil-only systems.

Key Features

• Material: EPDM construction offers strong resistance to ozone, sunlight and weathering for outdoor and exposed installations.
• Durometer: 70A firmness balances flexibility and compression set resistance so the rings maintain a seal under moderate pressure.
• Size accuracy: Nominal 4 in ID with actual measured dimensions close to specification to fit AS568 standard grooves reliably.
• Temperature range: Wide operating range from -55C to 125C so these rings can be used in low-temperature and many hot-water and steam applications.
• Chemical compatibility: Performs well with alcohols, dilute acids and alkalis, brake fluid, silicone oils and many hydraulic fluids, increasing versatility in maintenance environments.
• Pack quantity: Supplied as 25 pieces which is convenient for routine replacement cycles and inventory stocking.

Who It's For

This product suits maintenance technicians, HVAC and plumbing professionals, and industrial buyers who need a dependable EPDM seal in a common size for water, steam up to moderate temperatures, and many polar solvents. The pack size and predictable dimensions make it useful for stocking spares and for projects that require multiple identical seals.

It is not the right choice for applications that require fluoroelastomers or nitrile for extended exposure to petroleum fuels, oils or concentrated nonpolar solvents, so buyers working primarily with fuels or aggressive hydrocarbons should consider alternative materials.

Pros & Cons

Pros

• Good weather and ozone resistance makes these rings durable for outdoor and aging-prone applications.
• 70A hardness provides a useful balance of flexibility and sealing force for many static and dynamic seals.
• Pack of 25 offers value for maintenance shops and repeat servicing needs.
• Broad chemical compatibility with water, alcohols, brake fluids and many hydraulic fluids.

Cons

• EPDM is unsuitable for continuous exposure to petroleum oils and aggressive hydrocarbons, limiting use in fuel systems.
• The durometer and size are fixed, so applications needing softer or harder compounds or nonstandard sizes will need a different item.

Specifications

Material	EPDM
Durometer	70A
Nominal dimensions	4 in ID, 4-3/8 in OD, 3/16 in CS
Actual dimensions	3.975 in ID, 4.395 in OD, 0.210 in CS
Metric dimensions	100.97 mm ID, 111.63 mm OD, 5.33 mm CS
Temperature range	-55C (-67F) to 125C (257F)
Quantity	Pack of 25

Our Verdict

The Mr O-Ring 345 EPDM 4 in kit is a practical, cost-effective choice for shops and field technicians who need reliable, weather-resistant seals for water, steam and many polar fluids. It offers consistent sizing, good low-temperature flexibility and enough chemical compatibility for broad maintenance use, though it should be avoided where petroleum compatibility is required.

Frequently Asked Questions

Are these rings compatible with hydraulic fluids?
Yes, they are compatible with many phosphate ester based hydraulic fluids and certain other hydraulic fluids called out in the product compatibility list.

Can these be used in steam applications?
They can be used with steam up to approximately 204.4C (400F) in intermittent or specific service conditions noted for EPDM compatibility.

Do the sizes match AS568 standards?
Yes, the rings are designed to meet AS568 size standards with the nominal and actual dimensions provided for accurate fit.