Choosing the right O-ring involves more than just size and material. One of the most critical but often overlooked factors is the material hardness. This indicates how soft or firm a rubber compound is, influencing how well the O-ring seals, resists pressure, and performs in real-world conditions.

For most O-ring applications, Shore A hardness (abbreviated ShA or HA) is the primary scale used. However, understanding how different Shore scales work provides important context for making the best choice.

What Is Shore Hardness?

Shore hardness is a measure of how resistant a material is to indentation, indicating how soft or hard it is on a standardised scale. It is determined using a device called a durometer, which applies a standardised force to a material and measures its resistance to indentation. The result is a numerical value that helps compare the hardness of different materials.

Overview of Shore Hardness Scales

There are several Shore scales, but the most commonly used for polymers and elastomers are:

• Shore A (ShA or HA): Used for soft, flexible materials like rubber, silicone, and other elastomers. This is the standard scale for O-rings. The scale ranges from 0 (very soft) to 100 (very hard). For example, a 70 ShA O-ring offers a balance of flexibility and durability.
• Shore D (ShD or HD): Designed for harder plastics such as nylon, polycarbonate, and rigid thermoplastics. Shore D is not used for standard rubber O-rings, but may be referenced for rigid back-up rings (PTFE) or non-elastomeric sealing components.
• Shore 00: Less common in O-ring applications, Shore 00 is used for very soft gels or foams, like sponge rubber or soft silicone gels.

Which Shore A Hardness Rating is Best for your Application

The Shore A hardness rating of an O-ring has a direct impact on its ability to seal, resist deformation, and withstand pressure. As a guide what rating should you use for different applications.

• Soft O-rings (40–60 ShA): Highly flexible, excellent for low-pressure applications or when sealing against rough or uneven surfaces. However, they may wear more quickly and be prone to extrusion under high pressure.
• Medium O-rings (70 ShA): The most commonly used hardness for O-rings, striking a balance between elasticity and strength. Suitable for both dynamic and static sealing in hydraulics and pneumatics.
• Hard O-rings (80–90 ShA): Best for high-pressure environments. These O-rings are more resistant to extrusion and abrasion but require smooth sealing surfaces and higher installation force.

Reduce Cost and Downtime by Getting your Selection Right

Understanding the Shore Hardness scale, especially Shore A (ShA) for elastomers, is essential for selecting the right O-ring. By matching the material hardness to your application's requirements, you can ensure a more reliable, longer-lasting seal that minimises downtime and maintenance.  To find out more contact our team of experts.

Polymax EPDM O-Rings WRAS Certified for Safe Use in Drinking Water Applications

We are pleased to announce that Polymax EPDM O-rings have officially received WRAS (Water Regulations Advisory Scheme) approval, a mark of quality that guarantees compliance with UK water regulations. With Polymax WRAS approved EPDM O-rings, customers can have complete confidence that they are using high-quality, reliable products that meet stringent regulatory standards and perform consistently in every application.  Check out the official Polymax WRAS Listing on the WRAS Website

Our WRAS approved EPDM O-rings offer: Suitability for Drinking Water Systems: The primary benefit is that WRAS approval certifies that a non-metallic product is suitable for contact with drinking water, in compliance with standard BS 6920-1 / 2000. This makes them ideal for use in drinking water applications, such as water supply pipes and plumbing fixtures.

Compliance with UK Regulations: WRAS is the standard used in Great Britain for this purpose. Using WRAS-approved components helps ensure compliance with UK water regulations.

Assured Water Quality: The testing process for WRAS approval ensures that the elastomer materials do not impair the quality of the water they come into contact with. This includes verifying that the material does not: Promote the growth of bacteria Affect the water's colour or appearance Impart any unpleasant taste to the water This milestone reinforces Polymax’s commitment to bringing valuable solutions to the market, in particular where compliance and safety are paramount.